Note: Descriptions are shown in the official language in which they were submitted.
I
CO-INJECTION OF AROMATIC AND PARAFFINIC SOLVENTS DURING AN IN SITU
STARTUP PROCESS
TECHNICAL FIELD
[1] The technical field generally relates to startup processes for
mobilizing
bitumen contained in bitumen-bearing reservoirs, and more particularly to the
use of
startup fluids to enhance startup procedures of solvent-assisted recovery
processes.
BACKGROUND
[2] There are various techniques for in situ recovery of heavy
hydrocarbons, -
such as heavy oil and/or bitumen, from heavy hydrocarbon-bearing reservoirs.
Some
techniques are solvent-assisted recovery processes that employ a solvent to
help
mobilize the bitumen for recovery. Some solvent-assisted recovery processes
can have
similarities with conventional Steam-Assisted Gravity Drainage (SAG D),
although solvent
is injected into the heavy hydrocarbon-bearing reservoir instead or along with
steam.
[3] In one solvent-assisted recovery process, a pair of horizontal wells
including
an upper injection well and a lower production well can be provided in the
heavy
hydrocarbon-bearing reservoir, which can be an oil sands reservoir. The region
between
the injection well and the production well, i.e., the interwell region, is
characterized by
various levels of hydrocarbon saturation and fluid mobility, and will
generally include a
region having a high saturation of hydrocarbons and a limited fluid mobility.
The general
goal of the startup process is to increase the mobility of the hydrocarbons in
the interwell
region, for instance by warming the interwell region using various methods,
such as
using electric resistive heaters or providing steam circulation, and injecting
a mobilizing
fluid, such as solvent, into the hydrocarbon-bearing reservoir via the
injection well.
[4] Once fluid communication is established in the region between the
injection
well and the production well, injection of mobilizing fluid can continue in
order to promote
growth of an extraction chamber in proximity of the injection well. The
extraction
chamber eventually extends upwardly and outwardly from the injection well
within the
reservoir as the mobilized hydrocarbons flow toward the production well mainly
due to
viscous forces and gravity forces. Over time, a production fluid including the
mobilized
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hydrocarbons and a portion of the mobilizing fluid is recovered to the
surface. The
extraction chamber can be formed using various mobilizing fluids, such as
steam,
various hydrocarbon solvents, non-condensable gases, and combinations thereof.
[5] Various challenges still exist with regard to solvent-assisted recovery
processes and there is a need for enhanced technologies.
SUMMARY
[6] In accordance with one aspect, there is provided a startup process for
mobilizing
bitumen in an interwell region, the interwell region being defined between a
horizontal
injection section of an injection well and a horizontal production section of
a production
well located below the horizontal injection section, the injection well and
the production
well being located in a bitumen-containing reservoir. The startup process
comprises:
introducing a startup fluid comprising a non-deasphalting mobilizing solvent
and a
deasphalting mobilizing solvent into the bitumen-containing reservoir via the
injection
well, the non-deasphalting mobilizing solvent and the deasphalting mobilizing
solvent
being provided in a first stage proportion; recovering mobilized bitumen from
the interwell
region via the production well as a production fluid to form a bitumen-
depleted region
that enables fluid communication between the injection well and the production
well; and
transitioning the startup fluid from the first stage proportion to a second
stage proportion,
the second stage proportion having a reduced amount of the non-deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent compared to
the first
stage proportion; wherein at least the first stage proportion of the startup
fluid enables
asphaltenes to remain substantially solubilized in the mobilized bitumen.
[7] In some implementations, transitioning the startup fluid from the first
stage
proportion to the second stage proportion comprises a continuous transition.
[8] In some implementations, transitioning the startup fluid from the first
stage
proportion to the second stage proportion comprises a step transition.
[9] In some implementations, the second stage proportion enables the
asphaltenes
to remain substantially solubilized in the mobilized bitumen.
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[10] In some implementations, the second stage proportion enables
precipitation of at
least a portion of the asphaltenes such that asphaltene precipitates are
formed.
[11] In some implementations, the process further comprises transitioning
the startup
up fluid from the second stage proportion to a third stage proportion.
[12]. In some implementations, transitioning the startup fluid from the second
stage
proportion to the third stage proportion comprises a continuous transition.
[13] In some implementations, transitioning the startup fluid from the
second stage
proportion to the third stage proportion comprises a step transition.
[14] In some implementations, the third stage proportion has an increased
amount of
non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent
compared to the second stage proportion.
[15] In some implementations, the third stage proportion is substantially
free of the
deasphalting mobilizing solvent.
[16] In some implementations, the third stage proportion enables the
asphaltenes to
remain substantially solubilized in the mobilized bitumen.
[17] In some implementations, the process further comprises maintaining the
startup
fluid in the third stage proportion for a given period of time to resolubilize
the asphaltene
precipitates.
[18] In some implementations, the third stage proportion has a reduced amount
of
non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent
compared to the second stage proportion.
[19] In some implementations, maintaining the startup fluid in the third
stage
proportion and recovering the mobilized bitumen as the production fluid from
the
interwell region via the production well is performed substantially
simultaneously.
[20] In some implementations, the third stage proportion allows
precipitation of at
least a portion of the asphaltenes.
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[21] In some implementations, the startup fluid further comprises steam.
[22] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises vapourizing at least the non-deasphalting mobilizing
solvent at
surface to obtain a vapourized non-deasphalting mobilizing solvent; combining
the
vapourized non-deasphalting mobilizing solvent with the deasphalting
mobilizing solvent
to obtain a vapourized startup fluid; and injecting the vapourized startup
fluid into the
interwell region via the injection well.
[23] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises vapourizing the startup fluid at surface to obtain a
vapourized
startup fluid and injecting the vapourized startup fluid into the interwell
region via the
injection well.
[24] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises heating the startup fluid as the startup fluid travels
along the
injection well to obtain a vapourized startup fluid and injecting the
vapourized startup
fluid into the interwell region via the injection well.
[25] In some implementations, heating the startup fluid as the startup
fluid travels
along the injection well comprises providing electrically heating using one or
more
electric resistive heaters in the injection well.
[26] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir further comprises injecting the startup fluid via the production
well prior to
recovering the mobilized bitumen from the interwell region via the production
well.
[27] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir further comprises injecting the startup fluid via the production
well cyclically
between periods of recovering the mobilized bitumen from the interwell region
via the
production well.
[28] In some implementations, at least the first stage proportion further
enables
formation of a startup chamber.
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[29] In some implementations, recovering the mobilized bitumen via the
production
well and the formation of the startup chamber are performed substantially
simultaneously.
[30] In some implementations, the process further comprises determining
startup
chamber size.
[31] In some implementations, transitioning the startup fluid from the
first stage
proportion to the second stage proportion or from the second stage proportion
to the
third proportion is performed when the startup chamber size has reached a
given size.
[32] In some implementations, the process further comprises determining an.
amount
of mobilized bitumen produced from the interwell region to assess bitumen de-
saturation
in the interwell region.
[33] In some implementations, when the amount of mobilized bitumen produced
from
the interwell region is above a given threshold, the first stage proportion is
transitioned to
the second stage proportion.
[34] In some implementations, the process further comprises monitoring a
production
variable related to recovering the production fluid.
[35] In some implementations, the production variable comprises a
compositional
characteristic of the production fluid.
[36] In some implementations, the compositional characteristic comprises a non-
deasphalting mobilizing fluid concentration in the production fluid.
[37] In some implementations, the compositional characteristic of the
production fluid
cornprises a deasphalting mobilizing fluid concentration in the production
fluid.
[38] In some implementations, the compositional characteristic of the
production fluid
comprises a bitumen concentration of the production fluid.
[39] In some implementations, the compositional characteristic of the
production fluid
comprises an asphaltene content of the production fluid.
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[40] In some implementations, the compositional characteristic of the
production fluid
comprises an API gravity of the production fluid.
[41] In some implementations, in the first stage proportion, a ratio of non-
deasphalting
mobilizing solvent to deasphalting mobilizing solvent is above or equal to
about 1:1.
[42] In some implementations, in the first stage proportion, a ratio of non-
deasphalting
mobilizing solvent to deasphalting mobilizing solvent is between 1:1 and 3:1.
[43] In some implementations, in the second stage proportion, the ratio of
non-
deasphalting mobilizing =solvent to deasphalting mobilizing solvent is below
or equal to
1:1.
[44] In some implementations, in the first stage proportion, the ratio of
non-
deasphalting mobilizing solvent to deasphalting mobilizing solvent is between
about 1:1
and about 1:3.
[45] In some implementations, wherein in the first stage proportion, the
startup fluid
comprises between about 30% and about 50% of the non-deasphalting mobilizing
solvent and between about 50% and about 70% deasphalting mobilizing solvent.
[46] In some implementations, the non-deasphalting mobilizing fluid
comprises an
aromatic solvent.
[47] In some implementations, the aromatic solvent comprises toluene,
diesel, xylene,
or a combination thereof.
[48] In some implementations, the aromatic solvent comprises toluene.
[49] In some implementations, the aromatic solvent comprises diesel.
[50] In some implementations, the aromatic solvent comprises xylene.
[51] In some implementations, the deasphalting mobilizing fluid comprises an
alkane
solvent.
=
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[52] In some implementations, the alkane solvent comprises propane, butane,
pentane, hexane, heptane, condensate, or a mixture thereof.
[53] In some implementations, the alkane solvent comprises propane.
[64] In some implementations, the alkane solvent comprises butane.
[55] In some implementations, the alkane solvent comprises pentane.
[56] In some implementations, the alkane solvent comprises condensate.
[57] In some implementations, the process further comprises pre-heating the
interwell
region.
[58] In some implementations, pre-heating the interwell region comprises
electrically
heating using one or more electric resistive heaters in the injection well
and/or the
production well.
[59] In In some implementations, pre-heating the interwell region comprises
circulating steam through the injection well and/or the production well.
[60] In some implementations, the process further comprises separating the
production fluid to remove water and solids therefrom to obtain a solvent-rich
fluid.
= [61] In some implementations, the process further comprises separating
the solvent-
rich fluid to recover at least a portion of the deasphalting mobilizing
solvent and obtain a
recycled deasphalting mobilizing solvent suitable for reuse in the startup
fluid, and a
mixed bitumen and non-deasphalting mobilizing solvent stream.
[62] In some implementations, the process further comprises separating the
mixed
bitumen and non-deasphalting mobilizing solvent stream to recover at least a
portion of
the non-deasphalting mobilizing solvent to obtain a recycled non-deasphalting
mobilizing
solvent suitable for reuse in the startup fluid.
[63] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises introducing at least a portion of the recycled
deasphalting mobilizing
solvent as part of the startup fluid.
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[64] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises introducing at least a portion of the recycled non-
deasphalting
mobilizing solvent as part of the startup fluid.
[65] In accordance with another aspect, there is provided a startup process
for
mobilizing bitumen in an interwell region, the interwell region being defined
between a
horizontal injection section of an injection well and a horizontal production
section of a
production well located below the horizontal injection section, the injection
well and the
production well being located in a bitumen-containing reservoir. The startup
process
comprises introducing a startup fluid comprising a non-deasphalting mobilizing
solvent
and a deasphalting mobilizing solvent into the bitumen-containing reservoir,
the startup
fluid having a first composition that enables asphaltenes to remain
substantially
solubilized in mobilized bitumen; recovering the mobilized bitumen from the
interwell
region as a production fluid to form a bitumen-depleted region that enables
fluid
communication between the injection well and the production well;
transitioning the
startup fluid from the first composition to a second composition, the second
composition
having a reduced amount of the non-deasphalting mobilizing solvent relative to
the
deasphalting mobilizing solvent compared to the first composition.
[66] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises injecting the startup fluid via the injection well.
[67] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises injecting the startup fluid via the production well prior
to recovering
the mobilized bitumen from the interwell region via the production well.
[68] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir further comprises injecting the startup fluid via the production
well cyclically
between periods of recovering the mobilized bitumen from the interwell region
via the
production well.
[69] In some implementations, the process further comprises pre-heating the
interwell
region.
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[70] In some implementations, pre-heating the interwell region comprises
electrically
heating using one or more electric resistive heaters in the injection well
and/or the
production well.
[71] In some implementations, pre-heating the interwell region comprises
circulating
steam through the injection well and/or the production well.
[72] In some implementations, transitioning the startup fluid from the
first composition
to the second composition comprises a continuous transition.
[73] In some implementations, transitioning the startup fluid from the
first composition
to the second composition comprises a step transition.
[74] In some implementations, in the second composition, the non-deasphalting
mobilizing solvent is changed to a second non-deasphalting mobilizing solvent.
[75] In some implementations, in the second composition, the deasphalting
mobilizing
solvent is changed to a second deasphalting mobilizing solvent.
[76] In some implementations, the second composition enables the asphaltenes
to
remain substantially solubilized in the mobilized bitumen.
[77] In some implementations, the second composition allows precipitation
of at least
a portion of the asphaltenes such that asphaltene precipitates are formed.
[78] In some implementations, the process further comprises transitioning
the startup
up fluid from the second composition to a third composition.
[79] In some implementations, transitioning the startup fluid from the second
composition to the third composition comprises a continuous transition.
[80] In some implementations, transitioning the startup fluid from the second
composition to the third composition comprises a step transition.
[81] In some implementations, the third composition has an increased amount of
non-
deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent compared
to the second composition.
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[82] In some implementations, the third composition is substantially free
of the
deasphalting mobilizing solvent.
[83] In some implementations, the third composition enables the asphaltenes to
remain substantially solubilized in the mobilized bitumen.
[84] In some implementations, the process further comprises maintaining the
startup
fluid in the third composition for a given period of time to resolubilize the
asphaltene
precipitates.
[85] In some implementations, the third composition has a reduced amount of
non-
deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent compared
to the second composition.
[86] In some implementations, maintaining the startup fluid in the third
composition
and recovering the mobilized bitumen as the production fluid from the
interwell region via
the production well is performed substantially simultaneously.
[87] In some implementations, the third composition allows precipitation of
at least a
portion of the asphaltenes.
[88] In some implementations, the startup fluid further comprises steam.
[89] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises vapourizing at least the non-deasphalting mobilizing
solvent at
surface to obtain a vapourized non-deasphalting mobilizing solvent; combining
the
vapourized non-deasphalting mobilizing solvent with the deasphalting
mobilizing solvent
to obtain a vapourized startup fluid; and injecting the vapourized startup
fluid into the
interwell region via the injection well.
[90] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises vapourizing the startup fluid at surface to obtain the
vapourized
startup fluid and injecting the vapourized startup fluid into the interwell
region via the
injection well.
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=
[91] In some implementations, introducing the startup fluid into the
bitumen-containing
reservoir comprises heating the startup fluid as the startup fluid travels
along the
injection well to obtain a vapourized startup fluid and injecting the
vapourized startup
fluid into the interwell region via the injection well.
[92] In some implementations, heating the startup fluid as the startup
fluid travels
along the injection well comprises providing electrically heating using one or
more
electric resistive heaters in the injection well.
[93] In some implementations, at least the first composition further
enables formation
of a startup chamber.
[94] In some implementations, recovering the mobilized bitumen via the
production
well and the formation of the startup chamber are performed substantially
simultaneously.
[95] In some implementations, the process further comprises determining
startup
chamber size.
[96] In some implementations, transitioning the startup fluid from the
first composition
to the second composition or from the second composition to the third
composition is
performed when the startup chamber size has reached a pre-determined given
size.
[97] In some implementations, the process further comprises determining an
amount
of mobilized bitumen produced from the interwell region to assess bitumen de-
saturation
in the interwell region.
[98] In some implementations, when the amount of mobilized bitumen produced
from
the interwell region is above a given threshold, the first composition is
transitioned to the
second composition.
[99] In some implementations, the process further comprises monitoring a
production
variable related to recovering the production fluid.
[100] In some implementations, the production variable comprises a
compositional
characteristic of the production fluid.
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[101] In some implementations, the compositional characteristic comprises a
non-
deasphalting mobilizing fluid concentration in the production fluid.
[102] In some implementations, the compositional characteristic of the
production fluid
comprises a deasphalting mobilizing fluid concentration in the production
fluid.
[103] In some implementations, the compositional characteristic of the
production fluid
comprises a bitumen concentration of the production fluid.
[104] In some implementations, the compositional characteristic of the
production fluid
comprises an asphaltene content of the production fluid.
[105] In some implementations, the compositional characteristic of the
production fluid
comprises an API gravity of the production fluid.
[106] In some implementations, the non-deasphalting mobilizing fluid comprises
an
aromatic solvent.
[107] In some implementations, the aromatic solvent comprises toluene, diesel,
xylene,
or a combination thereof.
[108] In some implementations, the aromatic solvent comprises toluene.
[109] In some implementations, the aromatic solvent comprises diesel.
[110] In some implementations, the aromatic solvent comprises xylene.
[111] In some implementations, the deasphalting mobilizing fluid comprises an
alkane
solvent.
[112] In some implementations, the alkane solvent comprises propane, butane,
pentane, hexane, heptane, condensate, or a mixture thereof.
[113] In some implementations, the alkane solvent comprises propane.
[114] In some implementations, the alkane solvent comprises butane.
[115] In some implementations, the alkane solvent comprises pentane.
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[116] In some implementations, the alkane solvent comprises condensate.
[117] In some implementations, the process further comprises separating the
production fluid to remove water and solids therefrom to obtain a solvent-rich
fluid.
[118] In some implementations, the process further comprises separating the
solvent-
rich fluid to recover at least a portion of the deasphalting mobilizing
solvent and obtain a
recycled deasphalting mobilizing solvent suitable for reuse in the startup
fluid, and a
mixed bitumen and non-deasphalting mobilizing solvent stream.
[119] In some implementations, the process further comprises separating the
mixed
bitumen and non-deasphalting mobilizing solvent stream to recover at least a
portion of
the non-deasphalting mobilizing solvent to obtain a recycled non-deasphalting
mobilizing
solvent suitable for reuse in the startup fluid.
[120] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises introducing at least a portion of the recycled
deasphalting mobilizing
solvent as part of the stailup fluid.
[121] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises introducing at least a portion of the recycled non-
deasphalting
mobilizing solvent as part of the startup fluid.
[122] In accordance with another aspect, there is provided a startup process
for
mobilizing bitumen in an interwell region, the interwell region being defined
between a
horizontal injection section of an injection well and a horizontal production
section of a
production well located below the horizontal injection section, the injection
well and the
production well being located in a bitumen-containing reservoir. The startup
process
comprises introducing a startup fluid comprising a non-deasphalting mobilizing
solvent
and a deasphalting mobilizing solvent into the bitumen-containing reservoir,
the startup
fluid being provided with a proportion of the non-deasphalting mobilizing
solvent relative
to the deasphalting mobilizing solvent such that the startup fluid has a first
functionality,
the first functionality comprising enabling asphaltenes to remain
substantially solubilized
in mobilized bitumen; reducing the proportion of the non-deasphalting
mobilizing solvent
relative to the deasphalting mobilizing solvent until the startup fluid
reaches a second
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functionality; and recovering the mobilized bitumen from the interwell region
as a
production fluid to form a bitumen-depleted region that enables fluid
communication
between the injection well and the production well.
[123] In some implementations, the second functionality is a decreased
solubility of
asphaltenes in the mobilized bitumen.
[124] In some implementations, the decreased solubility of asphaltenes in the
mobilized bitumen allows precipitation of at least a portion of the
asphaltenes such that
asphaltene precipitates are formed.
[125] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises injecting the startup fluid via the injection well.
[126] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises injecting the startup fluid via the production well prior
to recovering
the mobilized bitumen from the interwell region via the production well.
[127] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir further comprises injecting the startup fluid via the production
well cyclically
between periods of recovering the mobilized bitumen from the interwell region
via the
production well.
[128] In some implementations, the process further comprises pre-heating the
interwell
region.
[129] In some implementations, pre-heating the interwell region comprises
electrically
heating using one or more electric resistive heaters in the injection well
and/or the
production well.
[130] In some implementations, pre-heating the interwell region comprises
circulating
steam through the injection well and/or the production well.
[131] In some implementations, reducing the proportion of the non-deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent comprises a
continuous
transition.
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[132] In some implementations, reducing the proportion of the non-deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent comprises a
step
transition.
[133] In some implementations, the startup fluid further comprises steam.
[134] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises vapourizing at least the non-deasphalting mobilizing
solvent at
surface to obtain a vapourized non-deasphalting mobilizing solvent; combining
the
vapourized non-deasphalting mobilizing solvent with the deasphalting
mobilizing solvent
to obtain a vapourized startup fluid; and injecting the vapourized startup
fluid into the
interwell region via the injection well.
[135] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises vapourizing the startup fluid at surface to obtain the
vapourized
startup fluid and injecting the vapourized startup fluid into the interwell
region via the
injection well.
[136] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises heating the startup fluid as the startup fluid travels
along the
injection well to obtain a vapourized startup fluid and injecting the
vapourized startup
fluid into the interwell region via the injection well.
[137] In some implementations, heating the startup fluid as the startup fluid
travels
along the injection well comprises , providing electrically heating using one
or more
electric resistive heaters in the injection well.
[138] In some implementations, at least the first functionality further
comprises enabling
formation of a startup chamber.
[139] In some implementations, recovering the mobilized bitumen via the
production
well and the formation of the startup chamber are performed substantially
simultaneously.
[140] In some implementations, the process further comprises determining
startup
chamber size.
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[141] In some implementations, the process further comprises determining an
amount
of mobilized bitumen produced from the interwell region to assess bitumen de-
saturation
in the interwell region.
[142] In some implementations, the process further comprises monitoring a
production
variable related to recovering the production fluid.
[143] In some implementations, the production variable comprises a
compositional
characteristic of the production fluid.
[144] In some implementations, the compositional characteristic comprises a
non-
deasphalting mobilizing fluid concentration in the production fluid.
[145] In some implementations, the compositional characteristic of the
production fluid
comprises a deasphalting mobilizing fluid concentration in the production
fluid.
[146] In some implementations, the compositional characteristic of the
production fluid
comprises a bitumen concentration of the production fluid.
[147] In some implementations, the compositional characteristic of the
production fluid
comprises an asphaltene content of the production fluid.
[148] In some implementations, the compositional characteristic of the
production fluid
comprises an API gravity of the production fluid.
[149] In some implementations, the non-deasphalting mobilizing fluid comprises
an
aromatic solvent.
[150] In some implementations, the aromatic solvent comprises toluene, diesel,
xylene,
or a combination thereof.
[151] In some implementations, the aromatic solvent comprises toluene.
[152] In some implementations, the aromatic solvent comprises diesel.
[153] In some implementations, the aromatic solvent comprises xylene.
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[154] In some implementations, the deasphalting mobilizing solvent comprises
an
alkane solvent.
[155] In some implementations, the alkane solvent comprises propane, butane,
pentane, hexane, heptane, condensate, or a mixture thereof.
[156] In some implementations, the alkane solvent comprises propane.
[157] In some implementations, the alkane solvent comprises butane.
[158] In some implementations, the alkane solvent comprises pentane.
[159] In some implementations, the alkane solvent comprises condensate.
[160] In some implementations, the process further comprises separating the
production fluid to remove water and solids therefrom to obtain a solvent-rich
fluid.
[161] In some implementations, the process further comprises separating the
solvent-
rich fluid to recover at least a portion of the deasphalting mobilizing
solvent and obtain a
recycled deasphalting mobilizing solvent suitable for reuse in the startup
fluid, and a
mixed bitumen and non-deasphalting mobilizing solvent stream.
[162] In some implementations, the process further comprises separating the
mixed
bitumen and non-deasphalting mobilizing solvent stream to recover at least a
portion of
the non-deasphalting mobilizing solvent to obtain a recycled non-deasphalting
mobilizing
solvent suitable for reuse in the startup fluid.
[163] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises introducing at least a portion of the recycled
deasphalting mobilizing
solvent as part of the startup fluid.
[164] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises introducing at least a portion of the recycled non-
deasphalting
mobilizing solvent as part of the startup fluid.
[165] In accordance with another aspect, there is provided a startup process
for
mobilizing bitumen in an interwell region, the interwell region being defined
between a
CA 3060946 2019-11-05
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horizontal injection section of an injection well and a horizontal production
section of a
production well located below the horizontal injection section, the injection
well and the
production well being located in a bitumen-containing reservoir. The startup
process
comprises introducing a startup fluid comprising at least a non-deasphalting
mobilizing
solvent in vapour phase into the bitumen-containing reservoir, the startup
fluid having a
first functionality; recovering mobilized bitumen from the interwell region as
a production
fluid to form a bitumen-depleted region that enables fluid communication
between the
injection well and the production well; and transitioning the startup fluid
from the first
functionality to a second functionality, comprising combining the non-
deasphalting
mobilizing solvent with a deasphalting mobilizing solvent; wherein the first
functionality of
the startup fluid comprises a formation of a startup chamber around the
injection well.
[166] In some implementations, transitioning the startup fluid from the first
functionality
to the second functionality comprises a continuous transition.
[167] In some implementations, transitioning the startup fluid from the first
functionality
to the second functionality comprises a step transition.
[168] In some implementations, the second functionality is a decreased
solubility of
asphaltenes in the mobilized bitumen.
[169] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises injecting the startup fluid via the injection well.
[170] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises injecting the startup fluid via the production well prior
to recovering
the mobilized bitumen from the interwell region via the production well.
[171] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir further comprises injecting the startup fluid via the production
well cyclically
between periods of recovering the mobilized bitumen from the interwell region
via the
production well.
[172] In some implementations, the process further comprises pre-heating the
interwell
region.
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[173] In some implementations, pre-heating the interwell region comprises
electrically
heating using one or more electric resistive heaters in the injection well
and/or the
production well.
[174] In some implementations, pre-heating the interwell region comprises
circulating
steam through the injection well and/or the production well.
[175] In some implementations, the startup fluid further comprises steam.
[176] In some implementations, introducing the startup fluid having the first
functionality
into the bitumen-containing reservoir in vapour phase comprises vapourizing
the at least
the non-deasphalting mobilizing solvent at surface to obtain a vapourized
startup fluid
and injecting the vapourized startup fluid into the interwell region via the
injection well.
[177] In some implementations, introducing the startup fluid having the first
functionality
into the bitumen-containing reservoir comprises heating the startup fluid as
the startup
fluid travels along the injection well to obtain a vapourized startup fluid
and injecting the
vapourized startup fluid into the interwell region via the injection well.
[178] In some implementations, heating the startup fluid as the startup fluid
travels
along the injection well comprises providing electrically heating using one or
more
electric resistive heaters in the injection well.
[179] In some implementations, recovering the mobilized bitumen via the
production
' well and the formation of the startup chamber are performed substantially
simultaneously.
[180] In some implementations, the process further comprises transitioning the
startup
fluid from the second functionality to a third functionality, wherein the
startup fluid having
the third functionality has a reduced amount of the non-deasphalting
mobilizing solvent
relative to the deasphalting mobilizing solvent compared to the startup fluid
having the
second functionality.
[181] In some implementations, the process further comprises determining
startup
chamber size.
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[182] In some implementations, the process further comprises determining an
amount
of mobilized bitumen produced from the interwell region to assess bitumen de-
saturation
in the interwell region.
[183] In some implementations, the process further comprises monitoring a
production
variable related to recovering the production fluid.
[184] In some implementations, the production variable comprises a
compositional
characteristic of the production fluid.
[185] In some implementations, the compositional characteristic comprises a
non-
deasphalting mobilizing fluid concentration in the production fluid.
[186] In some implementations, the compositional characteristic of the
production fluid
comprises a deasphalting mobilizing fluid concentration in the production
fluid.
[187] In some implementations, the compositional characteristic of the
production fluid
comprises a bitumen concentration of the production fluid.
[188] In some implementations, the compositional characteristic of the
production fluid
comprises an asphaltene content of the production fluid.
[189] In some implementations, the compositional characteristic of the
production fluid
comprises an API gravity of the production fluid.
[190] In some implementations, the non-deasphalting mobilizing solvent
comprises an
aromatic solvent.
[191] In some implementations, the aromatic solvent comprises toluene, diesel,
xylene,
or a combination thereof.
[192] In some implementations, the aromatic solvent comprises toluene.
[193] In some implementations, the aromatic solvent comprises xylene.
[194] In some implementations, the deasphalting mobilizing fluid comprises an
alkane
solvent.
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[195] In some implementations, the alkane solvent comprises propane, butane,
pentane, hexane, heptane, condensate, or a mixture thereof.
[196] In some implementations, the alkane solvent comprises propane.
[197] In some implementations, the alkane solvent comprises butane.
[198] In some implementations, the alkane solvent comprises pentane.
[199] In some implementations, the alkane solvent comprises condensate.
[200] In some implementations, the process further comprises separating the
production fluid to remove water and solids therefrom to obtain a solvent-rich
fluid.
[201] In some implementations, the process further comprises separating the
solvent-
rich fluid to recover at least a portion of the deasphalting mobilizing
solvent and obtain a
recycled deasphalting mobilizing solvent suitable for reuse in the startup
fluid, and a
mixed bitumen and non-deasphalting mobilizing solvent stream.
[202] In some implementations, the process further comprises separating the
mixed
bitumen and non-deasphalting mobilizing solvent stream to recover at least a
portion of
the non-deasphalting mobilizing solvent to obtain a recycled non-deasphalting
mobilizing
solvent suitable for reuse in the startup fluid.
[203] In some implementations, introducing the startup fluid into the bitumen-
containing
reservoir comprises introducing at least a portion of the recycled non-
deasphalting
mobilizing solvent as part of the startup fluid.
[204] In accordance with another aspect, there is provided a startup process
for
mobilizing bitumen in an interwell region, the interwell region being defined
between a
horizontal injection section of an injection well and a horizontal production
section of a
production well located below the horizontal injection section, the injection
well and the
=
production well being located in a bitumen-containing reservoir. The startup
process
comprises introducing a startup fluid comprising a non-deasphalting mobilizing
solvent
and a deasphalting mobilizing solvent into the bitumen-containing reservoir
via the
injection well, the non-deasphalting mobilizing solvent and the deasphalting
mobilizing
=CA 3060946 2019-11-05
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solvent being provided in a first stage proportion; recovering mobilized
bitumen from the
interwell region via the production well to form a bitumen-depleted region
that enables
fluid communication between the injection well and the production well; and
transitioning
the startup fluid from the first stage proportion to a second stage
proportion, the second
stage proportion having a reduced amount of the non-deasphalting mobilizing
solvent
relative to the deasphalting mobilizing solvent compared to the first stage
proportion.
[205] In some implementations, transitioning the startup fluid from the first
stage
proportion to the second stage proportion comprises a continuous transition.
[206] In some implementations, transitioning the startup fluid from the first
stage
proportion to the second stage proportion comprises a step transition.
[207] In some implementations, the second stage proportion enables
precipitation of at
least a portion of the asphaltenes such that asphaltene precipitates are
formed.
[208] In some implementations, the process further comprises, following the
transitioning of the startup fluid to the second stage proportion: halting
injection of the
deasphalting mobilizing solvent; injecting the non-deasphalting solvent; and
shutting in
the well for a given period of time to solubilize the asphaltene precipitates.
BRIEF DESCRIPTION OF THE DRAWINGS
[209] Figure 1 is a schematic representation of a well pair during a
startup process,
the well pair including an injection well and a production well located in a
hydrocarbon-
bearing reservoir, wherein a startup fluid is injected into the hydrocarbon-
bearing
reservoir via the injection well, including a representation of a zone
comprising mobilized
bitumen.
[210] Figure 2 is a schematic graph showing example proportions of a two-
component startup fluid for use during a startup process and in transition to
normal
recovery operations.
[211] Figure 3 is a schematic graph showing example proportions of a two-
component startup fluid for use during a startup process and in transition to
a normal
recovery operations.
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[212] Figure 4 is a schematic graph showing example concentrations of a non-
deasphalting mobilizing solvent and deasphalting mobilizing solvent as part of
a
multicomponent startup fluid that has at least two components for use during a
startup
process.
[213] Figure 5 is another schematic graph showing example concentrations of
a
non-deasphalting mobilizing solvent as part of an at least two-component
startup fluid for
use during a startup process.
[214] Figure 6 is another schematic graph showing example concentrations of
a
non-deasphalting mobilizing solvent as part of an at least two-component
startup fluid for
use during a startup process.
[215] Figure 7 is another schematic graph showing example concentrations of
a
non-deasphalting mobilizing solvent as part of an at least two-component
startup fluid for
use during a startup process.
= [216] Figure 8 is a flow diagram of a process for treating a
production fluid
recovered from a solvent-assisted recovery process using a startup fluid that
includes a
non-deasphalting mobilizing solvent and a deasphalting mobilizing solvent.
DETAILED DESCRIPTION
[217] Techniques described herein relate to startup processes for
mobilizing
bitumen contained in a bitumen-bearing reservoir, and concomitant development
of a
startup chamber, in the context of in situ bitumen recovery operations. The
startup
process includes at least two stages during which a startup fluid is injected
into the
reservoir, the startup fluid having a variable composition, for instance
depending of the
stage of the startup process.
[218] = The initial stage of the startup process includes introducing the
startup fluid
in vapour phase into the reservoir, where the startup fluid is initially
formulated as a non-
deasphalting composition that can include a non-deasphalting mobilizing
solvent and a
deasphalting mobilizing solvent in a first stage proportion. The first stage
proportion of
the non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing solvent in
=CA 3060946 2019-11-05
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the startup fluid enables mobilization of bitumen while avoiding precipitation
of
asphaltenes contained in the bitumen within the reservoir. In a subsequent
stage, the
first stage proportion of the non-deasphalting mobilizing solvent relative to
the
deasphalting mobilizing solvent is transitioned to a second proportion. The
transition
from the first stage proportion to the second stage proportion can be
achieved, for
instance, by reducing or ramping-down the proportion or amount of the non-
deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent. For
example, the ratio
or volume percentage of the non-deasphalting mobilizing solvent can be
decreased in
the startup fluid either continuously or using one or more step changes. Using
such a
staged approach with an initial composition that does not precipitate
asphaltenes,
followed by a transition to compositions that can induce asphaltene
precipitation can
advantageously promote startup chamber growth during the startup process while
.
mobilizing bitumen. The staged approach can also include stage(s) wherein
either one of
the non-deasphalting mobilizing solvent or the deasphalting mobilizing solvent
is
introduced into the subsurface formation.
[219] Optionally, the initial stage of the startup process can be preceded
by at least
one pre-heating step to subject the bitumen contained in the subsurface
formation to
various levels of pre-heating and facilitate its mobilization. The pre-heating
can be
performed for a certain period of time until the bitumen has reached a certain
temperature, for example, at which point the first stage solvent fluid can be
injected into
the subsurface formation.
[220] In some implementations, the startup fluid injection phase of the
startup
process can be continued until the startup fluid is substantially free of non-
deasphalting
mobilizing solvent and the injected solvent vapour is substantially a
deasphalting
solvent. In other implementations, the startup process can include a stage
when the non-
deasphalting mobilizing solvent is no longer a component of the startup fluid.
As the
startup process gradually transitions to normal operations, the startup
chamber will
evolve to become a mobilizing fluid chamber, and recovery of a production
fluid that
includes mobilized bitumen, water and solids will be continued. The mobilizing
fluid
chamber can be a chamber that includes steam, solvent or both, depending on
the
mobilizing fluid that is introduced into the subsurface formation during
normal operations.
CA 3060946 2019-11-05
25
[221] A more detailed description of the startup process for use in the
context of a
solvent-assisted recovery process and associated implementations is provided
below.
Startup process of an in situ bitumen recovery process
[222] As mentioned above, the startup process described herein facilitates
mobilization of bitumen contained in a subsurface formation and growth of a
startup
chamber by using a startup fluid as a mobilizing fluid , the startup fluid
being formulated
differently depending on the stage of the startup procedure during which it is
injected,
i.e., over the course of the startup procedure. The bitumen within the
formation includes
various hydrocarbon components, including heavier asphaltenes and lighter
maltenes.
Mobilized bitumen can then be produced as production fluid from the subsurface
formation during normal recovery operations that follow the startup process.
It should be
understood that the startup process described herein can be implemented in the
context
of any suitable in situ recovery process adapted to produce mobilize bitumen
from a
subsurface formation, such as a Steam Assisted Gravity Drainage (SAGD) process
or a
solvent-assisted gravity drainage operation. A SAGD process uses steam alone
as a
mobilizing fluid for introduction in the subsurface formation, whereas a
solvent-assisted
gravity drainage operation generally uses a solvent, with or without steam,
for
introduction into the subsurface formation. Once the startup process is
completed,
normal recovery operations of the in situ recovery process can follow.
[2231 Figure 1 shows an implementation of the startup process in the
context of an
in situ recovery process that is carried out via a horizontal well pair 10
provided in the
subsurface formation. The horizontal well pair 10 includes an injection well
12 overlying
a production well 14. The injection well 12 and the production well 14 are
generally
parallel and separated by an interwell region 16. The injection well 10
includes a vertical
portion 18 and a horizontal portion 20 extending from the vertical portion 14,
and the
production well 14 includes a vertical portion 22 and a horizontal portion 24
extending
from the vertical portion 22.
[224] Still referring to Figure 1, the startup process includes
injecting a startup fluid
26 as a mobilizing fluid into the subsurface formation. In the illustrated
implementation,
the startup fluid 26 is injected into the subsurface formation via a tubing
string 28
CA 3060946 2019-11-05
26
inserted into the injection well 12. The injection well 12 generally includes
a casing in its
vertical portion 18, and a liner in its horizontal portion 20. The liner
extends within the
wellbore and can include injection ports such that, when the startup fluid 26
exits the
tubing string 28, the startup fluid 26 can fill the horizontal portion 20 of
the injection well
12 and penetrate into the subsurface formation through the injection ports.
Alternatively,
the liner can also include a slotted portion or a screen portion that allows
the startup fluid
26 to exit the injection well 12 and penetrate into the subsurface formation.
In some
implementations, devices that can include straddle packers, inflatable
packers, sleeves
and/or coiled tubing can be used to influence the interval at which the
startup fluid 26 is
injected into the subsurface formation. The startup fluid 26 can also be
injected via the
production well 14. In some implementations, when the startup fluid 26 is
injected via the
production well 14, it can be done for instance at the beginning of the
startup process
when recovery of mobilized bitumen has not started yet, i.e., in
implementations where
the production well 14 is not yet used to recover mobilized bitumen. In other
implementations, injection of the startup fluid 26 can also be done for given
periods of
time in between which mobilized bitumen recovery through the production well
14 can
resume to sustain formation of a bitumen-depleted region and of the startup
chamber. In
yet other implementations, the startup fluid can be injected into the
subsurface formation
via a single well configuration that is operated in a cyclic mode.
[225] The startup fluid 26 can be injected into the subsurface formation as
vapour.
The vaporization of the startup fluid 26 can occur at surface using
conventional heating
means. A heater string 30 can also be inserted in the injection well 12 to
provide heat to
the startup fluid 26 as it is being carried through the injection well 12 via
the tubing string
28, either to vapourize the startup fluid 26 prior to exiting from the tubing
string 28, or to
maintain the startup fluid 26 in vapour phase prior to exiting from the tubing
string 28 so
that upon exiting the injection well 12, the startup fluid 26 is in vapour
phase.
[226] In addition to vapourizing and/or maintaining the startup fluid 26 in
vapour
phase while the startup fluid 26 travels along the injection well 12, the
heater string 30
can also provide heat to the interwell region 16, for instance to pre-heat the
bitumen
prior to the injection of the startup fluid 26 into the subsurface formation.
In some
implementations, a heater (e.g., through electric resistive heaters, RF
heaters or other
heating means) can also be provided in the production well 14 to provide
additional heat
CA 3060946 2019-11-05
27
to the interwell region 16. More details regarding heating of the interwell
region 16 are
provided below.
Characteristics of the startup fluid
[227] The startup fluid can include at least two components, and have a
variable
composition or a variable functionality over time to advantageously leverage
the
properties of each of its components with regard to their effect on bitumen
and startup
chamber growth during the startup process. The startup fluid can include a non-
deasphalting mobilizing solvent and a deasphalting mobilizing solvent, the
proportion of
the non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing solvent
varying over the course of the startup process to obtain various effects on
the bitumen.
The startup process can also include stage(s) during which the startup fluid
includes
either one of a non-deasphalting mobilizing solvent or a deasphalting
mobilizing solvent.
[228] A non-deasphalting mobilizing solvent refers to a solvent that does not
induce
asphaltene precipitation when in contact with bitumen, while being able to
mobilize
bitumen via dissolution effects. Examples of non-deasphalting mobilizing
solvents can
include aromatic solvents, such as toluene, )rylene and diesel as well as
higher carbon
number solvents or other refining products. Another example of a non-
deasphalting
solvent is dimethyl ether. As the startup fluid is injected into the
subsurface formation as
vapour, i.e., the startup fluid exits the injection well and/or the production
well as vapour,
the non-deasphalting mobilizing solvent can be chosen such that vaporization
is enabled
in a temperature range at which the startup process is operated. The
temperature range
can be determined in part based on the requirement that the startup fluid be
injected in
the subsurface formation at a sufficiently high temperature such that the
startup fluid
=
remains in vapour phase until it contacts the bitumen. The temperature range
can also
be determined in part based on the requirement that the startup fluid be
injected in the
subsurface formation at a sufficiently low temperature that the deasphalting
mobilizing
solvent condenses once in the subsurface formation, especially on the surfaces
of the
startup chamber when the startup chamber has grown sufficiently.
[229] The
interwell region is characterized by various levels of oil or bitumen
saturation and various levels of fluid mobility. In some implementations,
prior to the
CA 3060946 2019-11-05
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startup process the interwell region can include a high saturation interval
having low fluid
mobility. For instance, an oil or bitumen saturation between the range of 50%
to 100%
can be considered a high saturation interval. The use of a non-deasphalting
mobilizing
solvent early in the startup process, for instance as the first mobilizing
fluid introduced in
the subsurface formation, can facilitate establishing fluid communication
between the
injection and production wells by promoting the flow of mobilized bitumen from
the
injection well to the production well. The use of a non-deasphalting
mobilizing solvent
can also facilitate avoiding precipitation of asphaltenes in proximity to the
injection well
and/or the production well, either early in the startup process or at any
other time during
the startup process. Precipitation of asphaltenes in proximity of the wells
can impair the
flow of solvent and of the mobilized bitumen in the interwell region and can
also increase
the risk of clogging of the wells. It is to be noted that in some
implementations, a chase
fluid, such as water, either as steam or as an aqueous liquid stream, can be
injected into
the reservoir to aid in establishing fluid communication in the interwell
region.
[230] A deasphalting mobilizing solvent refers to a solvent that has the
property of
promoting the precipitation of asphaltenes under certain conditions. Certain
paraffinic
solvents, also referred to as alkanes, such as propane, butane, pentane, and
condensates are examples of deasphalting mobilizing solvents. The solubility
of
asphaltenes in such paraffinic solvents is relatively low particularly at
higher solvent
concentrations. The introduction of paraffinic solvent into a subsurface
formation is
generally avoided during a startup process because of their impact on the
precipitation
of asphaltenes. As mentioned above, if asphaltenes are precipitated too early
in the
startup process, when the bitumen saturation in the interwell region is still
high, the flow
of mobilized bitumen can be impaired, and pore space and/or the wells can
become
clogged. On the other hand, a paraffinic solvent can advantageously contribute
to
growing a startup chamber around the injection well. The startup chamber can
be
developed as mobilized bitumen is being produced via the production well and
thus form
a bitumen-depleted region, thereby creating a space around the injection well,
which will
eventually grow to occupy the?interwell region and a region above the
injection well as
injection of the deasphalting mobilizing solvent continues.
[231] In accordance with the techniques described herein, in some
implementations, the startup fluid can initially be provided in a first stage
proportion for
CA 3060946 2019-11-05
29
introduction into the subsurface formation. The first stage proportion of the
startup fluid
refers to a startup fluid having a given proportion of the non-deasphalting
mobilizing
solvent relative to the deasphalting mobilizing solvent, the given proportion
being such
that asphaltenes remain substantially in solution when the startup fluid
contacts the
bitumen in the subsurface formation. In other words, the first stage
proportion of the
startup fluid is formulated to avoid asphaltene precipitation at the injection
conditions,
and thus generally has a lower concentration of the deasphalting mobilizing
solvent
compared to the concentration of the non-deasphalting mobilizing solvent. It
is to be
understood that the first stage proportion,can be achieved when other
components are
present in the startup fluid, for instance water or steam, but will generally
be expressed
using the proportion between the non-deasphalting mobilizing solvent relative
to the
deasphalting mobilizing solvent, this given proportion being such that
overall,
asphaltenes remain substantially in solution when contacted with the startup
fluid. In
some implementations, the amount of non-deasphalting mobilizing solvent in the
first
stage proportion can be lower than the amount of deasphalting mobilizing
solvent in the
startup fluid, as long as this proportion of non-deasphalting mobilizing
solvent relative to
the deasphalting mobilizing solvent results in a startup fluid that reduces
asphaltene
precipitation at the injection conditions.
[232]
Figures 2 and 3 illustrate possible implementations related to the
composition of the startup fluid, with varying proportions of the non-
deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent as the
startup process
evolves over time. Figures 4 to 7 illustrate other possible implementations of
the startup
fluid, showing the concentration of non-deasphalting mobilizing solvent as a
function of
time. Figures 2 and 3 show that at the beginning of the startup process, the
non-
deasphalting mobilizing solvent is provided in a first stage proportion 32
relative to the
deasphalting mobilizing solvent, the first stage proportion being exemplified
at
approximately 2:1. A 2:1 proportion means that the startup fluid comprises
twice as
much non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing solvent,
which can be expressed for instance in terms of volume. The first stage
proportion of the
non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent is
chosen such that asphaltenes remain in solution in the bitumen while enabling
mobilization of the bitumen in the interwell region. It is to be understood
that the
CA 3060946 2019-11-05
30
approximative 2:1 proportion is given as an example only, and that depending
on factors
such as the respective non-deasphalting mobilizing solvent and deasphalting
mobilizing
solvent used, the chosen proportion can vary substantially.
[233] The composition of the startup fluid can be expressed using various
other
units to illustrate the proportion of the non-deasphalting mobilizing solvent
relative to the
deasphalting mobilizing solvent, for instance vol%, mass % or mol%. Given
units can be
chosen for instance depending on the choice of components in the startup
fluid,
including the choice of non-deasphalting mobilizing solvent and deasphalting
mobilizing
solvent. Examples of first stage proportion of the non-deasphalting mobilizing
solvent
relative to the deasphalting mobilizing solvent can be about 30 wt% toluene as
non-
deasphalting mobilizing solvent and about 70 wt% butane as deasphalting
mobilizing
solvent, or about 50 wt% toluene and about 50 wt% butane. In some
implementations,
an example of a second stage proportion can be between about 5 wt% to 10 wt%
of
toluene as non-deasphalting mobilizing solvent, and between about 90 wt% and
95 wt%
of butane as deasphalting mobilizing solvent.
[234] The choice of the first stage proportion can depend on various
factors such
as bitumen saturation in the interwell region, nature of non-deasphalting and
deasphalting mobilizing solvents and reservoir geology. Determining the first
stage
proportion can be done such that each one of the non-deasphalting mobilizing
solvent
and the deasphalting mobilizing solvent can have an impact on the startup
process with
regard to bitumen mobilization and startup chamber growth. In other words, the
first
stage proportion of the startup fluid can include a sufficiently high amount
of non-
deasphalting mobilizing" solvent such that asphaltene precipitation is avoided
and
formation of a startup chamber is facilitated, and a sufficiently high amount
of
deasphalting mobilizing solvent to contribute to startup chamber growth. In
some
implementations, allowing concomitant mobilization of bitumen and startup
chamber
growth can thus be advantageous in terms of reducing the duration of startup
process.
[235] Still referring to Figures 2 and 3, the startup fluid eventually
transitions from
the first stage proportion 32 to a second stage proportion 34. By
"transitioning", it is
meant that the proportion of non-deasphalting mobilizing solvent relative to
deasphalting
mobilizing solvent changes. Figure 2 shows the transition from the first,stage
proportion
CA 3060946 2019-11-05
31
32 to the second stage proportion 34 as a step change 36, whereas Figure 3
shows the
transition from the first stage proportion 32 to the second stage proportion
34 as a
=
continuous change 38. In both cases, the second stage proportion 34 has a
reduced
amount of non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing
solvent compared to the first stage proportion 32. In some implementations,
the startup
process described herein includes at least introducing the startup fluid into
the
subsurface formation in the first stage proportion for a given period of time,
and in the
second stage proportion for another given period on time. With reference to
Figure 2,
this means that the startup process includes at least the first stage
proportion 32, the
step change 36 and the second stage proportion 34. With reference to Figure 3,
the
startup process includes at least the first stage proportion 32, the
decreasing continuous
change 38 and the second stage proportion 34. Further reduction(s) of the
proportion of
the non-deasphalting mobilizing solvent relative to deasphalting mobilizing
solvent can
occur, which will be considered as extending the second stage of the startup
process. In
some implementations, reservoir parameters such as initial reservoir pressure
and
phase behavior of mobilizing solvent can influence when to transition from the
first stage
proportion to the second stage proportion, or when one or more subsequent
stage
proportions are to be implemented.
[236] In
some implementations and as shown in Figure 4, the startup fluid can
have a substantially continuous reduction of the proportion of the non-
deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent over time.
In such
implementations, the startup fluid is injected into the subsurface formation
as a first
stage startup fluid having a first functionality. The first functionality can
be, for instance
that asphaltenes remain in solution, i.e., to ensure that asphaltene
deposition does not
occur or is minimized in proximity of the wells, and/or that startup chamber
growth is
enabled. In other words, the first stage startup fluid can refer to a stage of
the startup
fluid that includes a continuous reduction, or continuous decline, in the
proportion of the
non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent. The
reduction, or ramp-down, of the non-deasphalting mobilizing fluid relative to
the
deasphalting mobilizing solvent can be continued for a given period of time,
until a
change in functionality of the startup fluid is desired, such that the
proportion of the non-
deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent allows
CA 3060946 2019-11-05
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benefiting from a second functionality of the startup fluid. For instance, the
first stage
startup fluid having a first functionality can be transitioned to a second
stage startup fluid
having a second functionality, the second functionality being enabling
accelerated
startup chamber growth, or allowing precipitation of asphaltenes. Of note, the
startup
process can also include a stage during which the startup fluid initially
includes a non-
deasphalting mobilizing solvent injected into the subsurface formation in
vapour phase
without a deasphalting mobilizing solvent to achieve the first functionality,
for instance
enabling the formation of a startup chamber, as exemplified in Figure 7.
[237] For instance, Figure 4 shows a first stage proportion 32 where the
non-
deasphalting mobilizing solvent has a given concentration in the startup
fluid, and that
concentration of the non-deasphalting mobilizing solvent decreases
continuously 38 until
the second stage proportion 34 is reached, while the concentration of
deasphalting
mobilizing solvent continuously increases. In the exemplified implementation
shown in
Figure 4, the first stage startup fluid corresponds to the combination of the
startup fluid
having a first stage proportion 32 at a given moment followed by the
continuous
decrease 38, the first stage startup fluid having a first functionality. Still
in the exemplified
implementation shown in Figure 4, the second stage startup fluid corresponds
to the
combination of the startup fluid having a second stage proportion 34 at a
given moment
followed by the continuous decrease 38, the second stage startup fluid having
a second
functionality.
[238] In some implementations, the startup process can also include
subsequent
reduction(s) of the proportion of the non-deasphalting mobilizing solvent
relative to the
deasphalting mobilizing solvent. For instance, with reference to Figure 2, the
startup fluid
in the second stage proportion 34 can be further transitioned to a third stage
proportion
40 with a step change 36 and so on. With reference to Figure 3, the startup
fluid can
also be further transitioned to a third stage proportion 40 with a decreasing
continuous
change 38 and so on. Of course, numerous paths can lead to the transition from
the first
stage proportion to the second stage proportion and optionally to subsequent
stage
proportions. It should thus be understood that the embodiments shown in
Figures 2 to 7
are examples only and that the reduction of the non-deasphalting mobilizing
solvent
relative to the deasphalting mobilizing solvent could occur in many other
ways, including
constant proportions of the non-deasphalting mobilizing fluid relative to the
deasphalting
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mobilizing fluid and/or continuous declines of the proportion of the non-
deasphalting
mobilizing fluid relative to the deasphalting mobilizing fluid.
[239] In some implementations, decreasing the proportion of the non-
deasphalting
mobilizing solvent relative to the deasphalting mobilizing solvent can allow
accelerated
growth of the startup chamber. Decreasing the proportion of the non-
deasphalting
mobilizing fluid relative to the deasphalting mobilizing fluid can eventually
reach a
proportion that, according to the characteristics of the bitumen and
reservoir, may lead to
precipitation of asphaltenes, for instance late in the startup process (i.e.,
close to the
beginning of normal recovery operations). It is important to note that
allowing
precipitation of asphaltenes in situ, i.e., in the reservoir, is preferably
done close to the
end of the startup process, when the interwell region has been cleaned and
bitumen
saturation has been substantially reduced. Thus, it is to be noted that the
second stage
proportion and optionally the subsequent stage proportions, as well as the
second
composition, are not one that will necessarily cause asphaltenes to
precipitate, even if
the non-deasphalting mobilizing solvent is reduced, as it is generally not
desirable in the
early phase of a bitumen recovery process to cause asphaltenes precipitation
in
proximity of a well pair. The second stage proportion and the second
composition can be
rather chosen such that startup chamber growth is enabled and/or accelerated.
[240] In some implementations, the reduction of the amount of non-
deasphalting
mobilizing solvent in the startup fluid can be such that eventually, the
startup fluid can be
substantially free of non-deasphalting mobilizing solvent, at which point in
time normal
recovery operations could be considered to begin. Other indicators can also
contribute to
determine when normal recovery operations can be considered to begin. For
instance, in
some implementations, normal recovery operations can be considered to begin
when the
startup chamber has reached a given size. The given size can be one where the
startup
chamber at least reaches the production well or is reasonably close to the
production
well. The given size can also be one where the startup chamber reaches the
production
well and rises above the injection well. Various techniques can be used to
assess
startup chamber growth and thus progression of startup process towards the
beginning
of normal recovery operations. For example, chamber growth and size can be
inferred
using observation wells, seismic analysis, as well as through analysis of the
production
fluid. For instance, components of the production fluid can be analyzed, and
it can be
CA 3060946 2019-11-05
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expected that in the beginning of the startup process, the production fluid
can include
mostly bitumen with connate water. On the other hand, near the end of the
startup
process, it can be expected that there will be a higher fraction of mobilizing
solvents in
the production fluid, compared to at the beginning of the startup process. In
some
implementations, growth of the startup chamber during the startup process can
facilitate
the initiation of the normal recovery operations.
[241] In some implementations, a reduction of the proportion of the non-
deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent can be
made possible because a certain portion of the non-deasphalting mobilizing
solvent has
accumulated at the interface between the startup chamber and bitumen. In such
implementations, the proportion of the non-deasphalting mobilizing solvent
relative to the
deasphalting mobilizing solvent is reduced as the asphaltene solubilizing
effect of the
non-deasphalting mobilizing solvent can be achieved relying on the presence of
non-
deasphalting mobilizing solvent already present and accumulated in the
reservoir.
Whether such scenario can occur can depend for instance on specific reservoir
conditions and recovery scheme, and is likely to occur near the end of the
startup
process.
[242] In some implementations, there can be scenarios where at some point
in
time in the startup process, the proportion of the non-deasphalting mobilizing
solvent
relative to the deasphalting mobilizing solvent is increased, for instance if
undesired
effects of the startup fluid on bitumen mobilization and/or chamber growth are
observed.
Such undesired effects can include recovery of a production fluid having a
significant
degree of bitumen upgrading early in the startup process, which can suggest
that
asphaltene precipitation has been occurring in the reservoir, an effect that
is generally to
be avoided. Another factor that can suggest whether it can be advantageous to
increase
the proportion of the non-deasphalting mobilizing solvent relative to the
deasphalting
mobilizing solvent is when an excessive pressure differential between the
injection well
and the production well is detected, which can be indicative of asphaltene
precipitation in
the interwell region. In such scenarios and with reference to Figure 6, a
corrective action
can thus be to adjust the proportion of the non-deasphalting mobilizing
solvent relative to
the deasphalting mobilizing solvent, and in particular to increase the
proportion of the
non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent so as
CA 3060946 2019-11-05 =
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to mitigate asphaltenes precipitation, for instance through an increasing
continuous
change 41. In Figure 6, the increasing continuous change 41 leads to the third
stage
proportion 40, which is then followed by a decreasing continuous change 38.
Another
scenario to consider can be that when monitoring the concentration of non-
deasphalting
solvent in the production fluid, it is observed that a low portion of non-
deasphalting
mobilizing solvent is being produced with the recovery of the production
fluid. Such
scenario can mean that a portion of the non-deasphalting mobilizing solvent
has
migrated within the reservoir such that the non-deasphalting mobilizing
solvent is less
effective at performing the maintaining in solution of the asphaltenes. This
scenario can
thus trigger an increase in the proportion of the non-deasphalting mobilizing
solvent
relative to the deasphalting mobilizing solvent, to mitigate this effect. In
the scenarios
discussed above, it is to be noted that the increase in the proportion of the
non-
deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent can be
such that the non-deasphalting mobilizing solvent is injected without any of
the
deasphalting mobilizing solvent, depending for instance on the extent of
asphaltene
precipitation that needs to be dealt with.
[243] As
mentioned above, the startup fluid can be introduced into the subsurface
formation in vapour phase, i.e., exit the injection well and/or the production
well in
vapour phase. When the startup fluid includes an aromatic solvent as the non-
deasphalting mobilizing solvent and a paraffinic solvent as the deasphalting
mobilizing
solvent, the higher vaporization temperature of aromatic solvents can
advantageously
provide sufficient heat for the paraffinic solvent to vapourize when the two
solvents are
combined. One approach to vapourize the startup fluid is thus to vapourize the
deasphalting mobilizing solvent at surface using conventional heating means
(e.g., a
direct fired heater or an indirect heat exchanger), such that when the non-
deasphalting
mobilizing solvent is then combined with the vapourized deasphalting
mobilizing solvent,
the non-deasphalting mobilizing solvent also vapourizes as it is carried with
the
vapourized deasphalting mobilizing solvent. In this scenario, the non-
deasphalting
mobilizing solvent can be simply fed as a liquid via a pipe intersection or
quill into the
pipeline carrying the vapourized deasphalting mobilizing solvent. In other
implementations, both the non-deasphalting mobilizing solvent and the
deasphalting
CA 3060946 2019-11-05
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mobilizing solvent are already in vapour phase when they are combined, and
thus are
combined as two vapour streams.
[244] This difference in vaporization temperature between the non-
deasphalting
mobilizing solvent and the deasphalting mobilizing solvent can also
advantageously
allow preferential condensation of the non-deasphalting mobilizing solvent in
the startup
chamber. Condensation of the non-deasphalting mobilizing solvent can enable
condensed non-deasphalting mobilizing solvent to drain by gravity towards the
production well and form a pool of non-deasphalting mobilizing solvent and
bitumen
around the production well, thereby facilitating eventual recovery of
mobilized bitumen.
On the other hand, the deasphalting mobilizing solvent can advantageously
remain as
vapour in the startup chamber for a longer period of time given its lower
vaporization
temperature, and preferably until it comes in contact with the surfaces of the
startup
chamber at which point it can condense, thereby contributing to the
mobilization of
bitumen by releasing latent heat of condensation and diluting the bitumen.
[245] In addition, as mentioned above, the startup process can include
stage(s)
during which either one of the non-deasphalting mobilizing solvent or the
deasphalting
mobilizing solvent can be introduced into the subsurface formation. These
scenarios can
occur at any time during the startup process, i.e., at the beginning of the
startup process,
during the startup process, or as the last stage of the startup process. The
injection of a
non-deasphalting mobilizing solvent without a deasphalting mobilizing solvent,
or the
injection of a deasphalting mobilizing solvent without a non-deasphalting
mobilizing
solvent, can be done according to the functionality of the startup fluid that
is desired to
be achieved.
[246] In some implementations, a non-deasphalting mobilizing solvent can be
introduced into the subsurface formation as vapour, without being combined
with a
deasphalting mobilizing solvent, to enable startup chamber growth. The use of
a
vaporized non-deasphalting mobilizing solvent can be advantageous, for
instance at the
beginning of the startup process, to enable formation of a startup chamber
while
avoiding precipitation of asphaltenes. In such implementations, the first
stage proportion
of the non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing solvent
would be considered to be 1:0, since the non-deasphalting mobilizing solvent
is injected
CA 3060946 2019-11-05
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without the deasphalting mobilizing solvent. Accordingly, in some
implementations, a
stage during which the startup fluid includes a non-deasphalting mobilizing
solvent that
is introduced into the subsurface formation in vapour phase without a
deasphalting
mobilizing solvent can correspond to the first stage of the startup process,
or to a startup
fluid having a first functionality. Examples of non-deasphalting mobilizing
solvents that
can be advantageous to use at the beginning of the startup process to grow the
startup
chamber are toluene and xylene, among others. A deasphalting mobilizing
solvent is
then subsequently combined with the non-deasphalting mobilizing solvent to
reach a
second stage proportion of the startup fluid, or to be transitioned to the
startup fluid
having a second functionality, in accordance with the implementations
described herein.
[247] In some implementations, a non-deasphalting mobilizing solvent can
also be
injected without a deasphalting mobilizing solvent at any stage during the
startup
process, for instance to remediate to asphaltene precipitation in the
interwell region or in
the wellbore. Such implementations are similar to those described above with
regard to
the proportion of the non-deasphalting mobilizing solvent relative to the
deasphalting
mobilizing solvent being increased during the startup process if undesired
effects of the
startup fluid on bitumen mobilization and/or chamber growth are observed,
although in
this case the proportion of the non-deasphalting mobilizing solvent relative
to the
deasphalting mobilizing solvent is increased up to a point where the non-
deasphalting
mobilizing solvent is injected without a deasphalting mobilizing solvent. This
includes
implementations wherein the non-deasphalting mobilizing solvent is injected
without the
deasphalting mobilizing solvent for a given period of time, until satisfactory
conditions of
the startup process are reached again, such as the composition of the
production fluid,
the pressure differential between the wells, etc. In some scenarios, the non-
deasphalting
mobilizing solvent can be injected without the deasphalting mobilizing solvent
and the
injection well can be shut in for a given period of time, for instance to
allow dissolution of
asphaltene precipitates that have formed. In other scenarios, a non-
deasphalting
mobilizing solvent can also be injected without the deasphalting mobilizing
solvent
during the recovery of production fluid to reduce the risk of asphaltene
precipitation.
[248] As mentioned above, in some implementations, the amount of non-
deasphalting mobilizing solvent in the startup fluid can be decreased such
that
eventually, the startup fluid can be substantially free of non-deasphalting
mobilizing
CA 3060946 2019-11-05
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solvent, which can be for instance near the end of the startup process. These
implementations are examples of scenarios where the injection of a
deasphalting
mobilizing solvent can be performed without a non-deasphalting mobilizing
solvent.
Again, depending on the functionality of the startup fluid that is to be
achieved, stage(s)
where the injection of the deasphalting mobilizing solvent is performed
without the non-
deasphalting mobilizing solvent can occur during the startup process, and not
just at the
end of the startup process, for instance to accelerate startup chamber growth.
[249] In some implementations, prior to the startup fluid being injected
into the
subsurface formation, a step of pre-heating can be performed to pre-heat the
bitumen
present in the interwell region to contribute to its mobilization. The pre-
heating step can
be performed by heating the injection well and optionally the production well
using
heater strings such as those described above, or through electric resistive
heaters, RF
heaters or other heating means. Alternatively, the pre-heating step can be
performed by
circulating steam in the injection well or any other pre-heating technique. In
some cases,
the heaters can continue operating during subsequent stages of the startup
processes,
such that the startup fluid is injected while the heaters continue to impart
heat to the
reservoir.
Monitoring variables related to startup process
[250] Various variables can be monitored to determine suitable second stage
proportions of the non-deasphalting mobilizing solvent relative to the
deasphalting
mobilizing solvent in the startup fluid (and optionally of third stage
proportions and so
on), the timing of the change from one stage proportion to another, and also
to assess,
whether the startup procedure can be considered to be terminated such that
transition
into the normal recovery operations can be initiated.
[251] Once the startup fluid has been injected into the subsurface
formation for a
given period of time, bitumen that has been mobilized by the presence of the
startup
fluid and optionally the heat provided during the pre-heating step, can drain
into the
production well by gravity and can be recovered to the surface using
artificial lift or a
pump (e.g., electric submersible pump or ESP) deployed in the production well.
A
compositional characteristic of the produced mobilized bitumen during the
startup
CA 3060946 2019-11-05
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process is an example of a variable that can be monitored. A compositional
characteristic of the produced mobilized bitumen can be, for instance, the
concentration
of the non-deasphalting mobilizing solvent, the concentration of the
deasphalting
mobilizing solvent in the produced mobilized bitumen, the asphaltene content
of the
mobilized bitumen, and/or the API gravity of the mobilized bitumen.
[262] In particular, the compositional characteristic of the produced
mobilized
bitumen can be indicative of the extent of cleanup, or bitumen de-saturation,
that has
occurred between the injection well and the production well. Bitumen de-
saturation
between the injection well and production well refers to the process of
substantially
reducing bitumen saturation in the interwell region, which can be achieved at
least in
part by the mobilization of bitumen and production of mobilized bitumen to the
surface.
De-saturation of the interwell region from bitumen thus can create a space
between the
injection well and the production well which can facilitate growth of the
startup chamber
described herein. Sufficient bitumen de-saturation of the interwell region can
be said to
be achieved for instance when solvent from the startup fluid is found in high
concentration in the production fluid (in which case the solvent can be said
to be back
produced). Other techniques that can be used to serve as indicators of bitumen
de-
saturation in the interwell region and thus the degree of interaction between
the injection
well and the production well can include analysis of pressure interaction
between the
wells, seismic analysis, use of observation well temperature readings, and
repeat
saturation logging.
[263] The asphaltene content of the produced mobilized bitumen can be
assessed
to determine whether the amount of non-deasphalting mobilizing solvent in the
startup
fluid is sufficient for asphaltenes to remain in solution, i.e., to ensure
that asphaltene
deposition does not occur or is minimized in proximity of the wells. For
instance, if the
asphaltene content of the produced mobilized bitumen is low, it could be
hypothesized
that asphaltenes are left in the subsurface formation as precipitates, which
is to be
avoided. On the other hand, if the asphaltene content in the produced
mobilized bitumen
is high, then it could be hypothesized that asphaltenes are solubilized in the
startup fluid
and are being removed from the subsurface formation with the produced
mobilized
bitumen.
CA 3060946 2019-11-05
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[254] Simulations can be performed to help predict which level of
asphaltene
content is to be expected for a given subsurface formation and/or given
combination and
proportion of non-deasphalting mobilizing solvent and deasphalting mobilizing
solvent as
components of the startup fluid. Thus, when such simulations are available,
one can
assess whether the asphaltene content of the produced mobilized bitumen is
below a
predetermined asphaltene content threshold. If the asphaltene content is above
the
predetermined asphaltene content threshold, then the composition of the
startup fluid
could be considered effective at least for the purpose of keeping the
asphaltenes in
solution such that the space between the injection well and the production
well can be
cleaned up. If the asphaltene content is below the predetermined asphaltene
content
threshold, then the amount of the deasphalting mobilizing solvent in the
startup fluid
could be reduced relative to the non-deasphalting mobilizing solvent, or the
amount of
the non-deasphalting mobilizing solvent in the startup fluid could be
increased relative to
the deasphalting mobilizing solvent to favor the solubilization of the
asphaltenes.
[255] In some implementations, the amount of non-deasphalting mobilizing
solvent
can be determined such that it is sufficient to keep the asphaltenes in
solution and to
facilitate the formation of a startup chamber, while being combined with a
sufficient
amount of deasphalting mobilizing solvent to also contribute to the growth of
the startup
chamber. Keeping the right balance between the amount of non-deasphalting
mobilizing
solvent and the amount of deasphalting mobilizing solvent in the startup fluid
can be
relevant to achieving concomitant mobilization of bitumen and startup chamber
growth.
This right balance can change as the startup process progresses and the
interwell space
becomes cleaner over time.
[256] The API gravity of the produced mobilized bitumen can also be
evaluated in
a similar fashion as the asphaltene content itself, as the API gravity can be
considered
indicative of the asphaltene content of the produced mobilized bitumen.
[257] As the startup process progresses and the interwell space becomes
cleaner,
the concentration of bitumen in the mobilized bitumen that is produced to the
surface
can decrease and include an increasing proportion of the startup fluid
solvents.
Monitoring the concentration of the non-deasphalting mobilizing solvent and/or
of the
deasphalting mobilizing solvent in the produced mobilized bitumen can be used
to
CA 3060946 2019-11-05
41
determine the timing of when the space can be considered clean enough that the
proportion of the non-deasphalting mobilizing solvent can be reduced or ramped-
down.
In other words, because the space around the injection well and the production
well is
now cleaned up, i.e., mobilized bitumen has been removed from the interwell
space, the
risk of asphaltene precipitates .forming and impairing the flow of mobilized
bitumen or,
clogging the wells is decreased. Accordingly, the startup fluid can include a
decreased
amount of non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing
solvent, because it is no longer as relevant to keep asphaltenes in solution
and the
startup fluid can rather be optimized to further grow the startup chamber
efficiently, for
instance to reduce operation costs. Over the course of the startup process,
the
composition of the produced mobilized bitumen can thus progressively evolve
from a
composition having a high bitumen content, to a composition having a moderate
bitumen
content with a low concentration of non-deasphalting mobilizing solvent, to a
composition having a low bitumen content and a high concentration of non-
deasphalting
mobilizing solvent. As mentioned above, the non-deasphalting mobilizing
solvent
condenses preferably in the startup chamber and can, produced with mobilized
bitumen,
while the deasphalting mobilizing solvent preferably remains as vapour in the
startup
chamber. Although the terms "high" and "low" are relative terms, they can
still show how
the composition of the production fluid can approximately evolve during the
startup
process.
[258] Another option to determine when it can be appropriate to reduce the
amount
of non-deasphalting mobilizing solvent relative to the deasphalting mobilizing
solvent is
to use volumetric simulations. Such volumetric simulations can provide an
estimate of a
given volume between the injection well and the production well, and once a
corresponding volume of mobilized bitumen has been produced to the surface, it
can be
expected that this volume of interwell region has been cleaned up. Once again,
when
the interwell region has been cleaned up, the startup fluid can include a
decreased
amount of non-deasphalting mobilizing solvent relative to the deasphalting
mobilizing
solvent at least because the interwell region has been substantially cleaned
from the
asphaltenes that could have potentially precipitated.
[259] Other types of simulations to determine the extent of cleanup around
the
wells include 4D seismic reservoir analysis to monitor changes in fluid
location and
CA 3060946 2019-11-05
42
saturation, pressure and temperature by evaluating the changes in the acoustic
and
elastic properties of the geological formation. Relevant data can also be
obtained from
strategically positioned observation wells.
[260] In some implementations, it may be advantageous that one or more
components of the startup fluid be changed over the course of the startup
process. In
such implementations, the startup fluid can include, in a first stage of the
startup
process, a first non-deasphalting mobilizing solvent and a first deasphalting
mobilizing
solvent provided in a first stage proportion that enables asphaltenes to
remain in
solution. When transitioning to a second stage of the startup process, the
first non-
deasphalting mobilizing solvent and the first deasphalting mobilizing solvent
of the
startup fluid are provided in a second stage proportion, such that the amount
of the first
non-deasphalting mobilizing solvent relative to the first deasphalting
mobilizing solvent is
reduced. Following the change to the second stage proportion, the first non-
deasphalting
mobilizing solvent can be changed to a second non-deasphalting mobilizing
solvent,
and/or the first deasphalting mobilizing solvent can be changed to a second
deasphalting mobilizing solvent to achieve given results on the mobilization
of the
bitumen and/or the startup chamber growth. For instance, in the first stage of
the startup
process, the startup fluid can include diesel as the first nonAeasphalting
mobilizing
solvent and butane as the first deasphalting mobilizing solvent in a first
stage proportion
that enables asphaltenes to remain in solution. In the second stage of the
startup
process, the amount of diesel can be ramped down relative to the amount of
butane,
such that the diesel and butane are provided in the second stage proportion.
Then, for
example, the diesel can be changed to toluene and/or the butane can be changed
to
propane. In some implementations, the new combination of non-deasphalting
mobilizing
solvent and deasphalting mobilizing solvent can facilitate achieving certain
characteristics of the startup chamber and/or preparing the reservoir for
effective
recovery during the normal operations.
[261] In other implementations, the startup fluid can be formulated as a
first
composition and include, in a first stage of the startup process, a first non-
deasphalting
mobilizing solvent and a first deasphalting mobilizing solvent provided such
that
asphaltenes remain in solution. When transitioning to a second stage of the
startup
process, the startup fluid can be transitioned to a second composition. In the
second
CA 3060946 2019-11-05
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composition, the first non-deasphalting mobilizing solvent can be changed to a
second
non-deasphalting mobilizing solvent and/or the first deasphalting mobilizing
solvent can
be changed to a second deasphalting mobilizing solvent. The second composition
can
be chosen so as to facilitate achieving certain characteristics of the startup
chamber
and/or preparing the reservoir for effective recovery during the normal
operations.
Implementations related to recovery of mobilized bitumen as production fluid
[262] As mentioned above, the startup fluid is introduced into the
subsurface
, formation to dilute and heat bitumen and produce mobilized bitumen. The
mobilized
bitumen can then drain into the production well and be recovered to the
surface as a
production fluid, which creates the space around the injection well. The
production fluid
thus recovered can have a variable composition depending on the stage of the
startup
process. Depending on different factors, such as the composition of the
production fluid
and economic considerations, it may be desirable to subject the production
fluid to one
or more separation steps, for instance to recover one or both of the non-
deasphalting
mobilizing solvent and the deasphalting mobilizing solvent. The recovered
mobilizing
solvents can then be used as recycled solvents in the startup fluid. In
implementations
where the non-deasphalting mobilizing solvent is an aromatic solvent and the
deasphalting mobilizing solvent is a paraffinic solvent, the difference
between their
respective vaporization temperatures can mean that different separation steps
are put in
place to recover each mobilizing solvent.
[263] With reference to Figure 8, a production fluid 42 is recovered during
the
startup process. The production fluid includes mobilized bitumen, water,
solids and at
least a portion of both solvents of the startup fluid. The production fluid 42
is subjected to
a first separation 44 to remove water and solids 46 as an underflow, and to
recover a
solvent-rich fluid 48 comprising mobilized bitumen and a portion of the
startup fluid as an
overflow. In some implementations, the first separation 44 can be performed
for instance
through gravity separation mechanisms. The composition of the solvent-rich
fluid 48 can
vary in accordance with the composition of the production fluid 42, in terms
of the
bitumen content and the respective concentrations of the non-deasphalting
mobilizing
solvent and the deasphalting mobilizing solvent. The solvent-rich fluid 48 is
then
subjected to a second separation 50 to recover a deasphalting mobilizing
solvent-rich
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44
stream 52 and a mixed bitumen and non-deasphalting mobilizing solvent stream
54. The
second separation 50 can be performed for instance in a flash vessel through
evaporation mechanisms to flash the deasphalting mobilizing solvent from the
solvent-
rich fluid 48. This separation technique can advantageously leverage the
difference in
vaporization temperature between the deasphalting mobilizing solvent and the
non-
deasphalting mobilizing solvent, such that the deasphalting mobilizing solvent
can be
selectively separated. The deasphalting mobilizing solvent-rich stream 52 can
be reused
as a component of the startup fluid for reintroduction into the subsurface
formation.
[264] In some implementations, the mixed bitumen and non-deasphalting
mobilizing solvent stream 54 can be further separated in a third separation
step 56 to
recover a non-deasphalting mobilizing solvent-rich stream 58 and a bitumen-
rich stream
60. In other implementations, it may be advantageous to keep the mixed bitumen
and
non-deasphalting mobilizing solvent stream 54 as a combined fluid, for
instance because
the presence of the non-deasphalting mobilizing solvent may act as a diluent,
such that
the mixed bitumen and non-deasphalting mobilizing solvent stream 54 may have
valuable characteristics in itself. In other implementations, the bitumen-rich
stream 60
can then be further processed to obtain a suitable bitumen product.
[265] Of note, although the first separation 44, the second separation 50
and the
third separation 56 are illustrated as a single step, each one of the first
separation 44,
the second separation 50 and the third separation 56 can include more than one
separation stage in order to achieve the desired separation.
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