Note: Descriptions are shown in the official language in which they were submitted.
ADJUSTMENT OF SOLVENT INJECTION RATE BASED ON STORAGE
TEMPERATURE FLUCTUATION IN STEAM-SOLVENT ASSISTED RECOVERY
PROCESS FOR HYDROCARBON RECOVERY
FIELD
[0001] The present disclosure relates generally to hydrocarbon recovery
from
subterranean reservoirs, and particularly to solvent injection control in in
situ steam-
solvent hydrocarbon recovery.
BACKGROUND
[0002] Steam and a solvent can be co-injected into a subterranean reservoir
of
bituminous sands (also commonly referred to as oil sands) to assist, drive, or
aid
hydrocarbon recovery from the reservoir (referred to herein as a steam-solvent
recovery process).
[0003] Typically, in a steam-solvent recovery process a desired ratio of
solvent to
steam (solvent-to-steam ratio) in the injection stream and the desired
injection
temperature and pressure are pre-determined, and the steam and solvent are
mixed at
constant respective amounts or rates according to these pre-determined values
before
injection by separately controlling the injection rate of steam and the
injection rate of
solvent so that the ratio of the solvent injection rate to the steam injection
rate is the
same as the desired solvent-to-steam ratio in the injection mixture, which has
been
determined to provide the desired temperature and pressure in the injection
mixture.
For example, for a given solvent injection rate (e.g. 35 t/d), the steam
injection rate
may be selected and controlled (e.g. selected to be 15 t/d) to obtain a weight
percentage of the solvent (e.g. 70 wt% solvent) in the injection mixture that
corresponds to the desired solvent to steam ratio (e.g. =3:7), which provides
the
desired mixture temperature and pressure. The solvent to steam ratio may be
based
Date Recue/Date Received 2020-11-02
on weight/mass, volume, mole, or a combination thereof, and may be expressed
or
indicated in the form of relative ratios, or percentages such as weight
percentages,
volume percentages, or molar percentages.
[0004] In a typical arrangement in a steam-solvent recovery process, an
input
stream of steam and an input stream of solvent may be provided through
separate
pipelines and mixed at a junction of the pipelines at surface before injection
into the
injection well, where the flow rate in each of the input pipeline is regulated
to achieve a
pre-selected target flow rate. The target flow rates are typically pre-
determined
according to the desired ratio of solvent to steam in the injection stream and
injection
temperature/pressure. For example, the target values of the required flow
rates in the
steam input pipeline and the solvent input pipeline for a given weight ratio
of solvent to
steam and a selected injection temperature can be pre-determined. The flow in
each
of the input pipelines may be controlled to achieve and maintain the pre-
determined
flow rate for that input line.
SUMMARY
[0005] It has been recognized by the present inventor(s) that maintaining
the same
flow rate of injected steam over a long period of time to achieve a constant
target
solvent-to-steam ratio in the injection mixture in a steam-solvent recovery
process may
not provide the optimal, e.g. more economical outcome in some situations. For
example, it has been recognized that when the temperature of the input solvent
before
mixing or injection with the steam is fluctuating, injecting the steam at a
correspondingly lower or higher rate depending on whether the input solvent
temperature is higher or lower may reduce or avoid steam wastage and may
optimize
steam injection. Thus, it would be beneficial to adjust the steam injection
rate at least
in part based on the real-time fluctuation of the solvent storage temperature.
[0006] Thus, in an aspect of the present disclosure, there is provided a
method of
injecting steam and solvent into a subterranean reservoir to assist recovery
of
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Date Recue/Date Received 2020-11-02
hydrocarbons therefrom, the method comprising injecting steam and a solvent
into the
reservoir; and adjusting a rate of steam injection based on real-time
fluctuation of a
storage temperature of the solvent to be injected.
[0007] In various embodiments, the storage temperature of the solvent may
be
dependent on fluctuation in solar energy transferred to the stored solvent
such as
through direct sunlight or other solar radiation, and the rate of steam
injection may be
adjusted to, at least in part, compensate for the fluctuation in the solar
energy
transferred to the stored solvent. In this process, a first stream comprising
steam at a
first temperature and a second stream comprising the solvent at a second
temperature
may be mixed to form a third stream comprising steam and the solvent at a
third
temperature. The first stream may flow at a first flow rate and the second
stream may
flow at a second flow rate, the first and second flow rates may be selected
based on a
target temperature for the third stream, and the second temperature may be
dependent on the storage temperature. The first flow rate of the first stream
may be
dynamically adjusted to compensate for real-time fluctuation in the second
temperature of the second stream to reduce a difference between the target
temperature and the third temperature of the third stream. The third stream
may be
then injected at the third temperature into the reservoir. Adjustment of the
first flow
rate may be based on actual fluctuation in the second temperature. The actual
fluctuation in the second temperature may be measured in real-time. Adjustment
of the
first flow rate may also be based on an expected change of the second
temperature.
The solvent may be stored in a container exposed to solar radiation such as
sunlight
during daytime, and the expected change of the second temperature may be
determined at least in part based on expected natural fluctuations in the
sunlight over
time. The natural fluctuations in the sunlight may comprise daily fluctuations
and
seasonal fluctuations. An exterior surface of the container may be coated with
a light
absorbing coating to increase heat energy absorbed by the container from the
sunlight, for increasing the second temperature. A solar panel may be provided
and
heat energy may be transferred from the solar panel to the container to
increase the
second temperature. More broadly, the solvent may be stored in a container
receiving
heat from an energy source, and the expected change of the second temperature
is
3
Date Recue/Date Received 2020-11-02
determined at least in part based on expected fluctuations of the amount of
heat
received from the energy source. The energy source may be an external energy
source (including an environmental thermal energy source), or an internal
energy
source (e.g. integrated with the storage container).
[0008] In a further aspect, there is provided a system for injecting steam
and
solvent into a subterranean reservoir to assist recovery of hydrocarbons
therefrom, the
system comprising: a first conduit for supplying a first stream comprising
steam; a
second conduit for supplying a second stream comprising a solvent; a third
conduit
connected to the first and second conduit for mixing the first and second
streams to
form a third stream and supplying the third stream comprising steam and the
solvent
for injection into the reservoir; a flow regulator in the first conduit for
regulating a first
flow rate of the first stream in the first conduit; a controller connected to
the flow
regulator, the controller configured and programmed to control the flow
regulator to
adjust the first flow rate of the first stream based on fluctuation in the
second
temperature of the second stream.
[0009] In various embodiments, the system may comprise a steam source
connected to the first conduit for supplying steam at selected temperature,
pressure
and steam quality. The flow regulator may comprise one or more valves. The
system
may comprise a solvent source connected to the second conduit for supplying
the
solvent at a selected second flow rate. The solvent source may comprise a
container
exposed to sunlight during daytime, and the controller may be programmed to
determine expected change in the second temperature at least in part based on
expected natural changes in the sunlight over time, and to adjust the first
flow rate
based on the expected change in the second temperature. An exterior surface of
the
container may comprise a light absorbing coating for increasing heat energy
absorbed
by the container from the sunlight. The system may further comprise a solar
panel
connected to the solvent source for generating heat energy from sunlight and
providing the heat energy to the solvent source to increase the second
temperature.
The system may comprise a temperature sensor associated with the second
conduit
for detecting the second temperature, wherein the controller is programed to
adjust the
4
Date Recue/Date Received 2020-11-02
first flow rate based on fluctuation in the detected second temperature. The
controller
may comprise a processor or a computer. The third conduit may be in fluid
communication with an injection well penetrating the reservoir for injecting
the third
stream into the reservoir through the injection well.
[0010] Other aspects, features, and embodiments of the present disclosure
will
become apparent to those of ordinary skill in the art upon review of the
following
description of specific embodiments of the disclosure in conjunction with the
accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the figures, which illustrate, by way of example only,
embodiments of the
present disclosure:
[0012] FIG. 1 is a schematic side view of a hydrocarbon reservoir and a
pair of
wells penetrating the reservoir for recovery of hydrocarbons.
[0013] FIG. 2 is schematic block diagram of a possible arrangement in the
surface
injection facility shown in FIG. 1, according to an embodiment of the present
disclosure.
[0014] FIG. 3 is a line graph showing representative temperature profiles
of a
solvent stored in a solvent storage tank and corresponding temperature profile
of the
local environmental temperature over a period of about a week.
[0015] FIG. 4 is a line graph showing representative temperature profiles
of the
corresponding steam/solvent mixture and the stored solvent, in response to the
local
environmental temperature fluctuation as shown in FIG. 4.
[0016] FIG. 5 is a schematic block diagram of a control system for control
the
steam and solvent injection in the system of FIG. 2.
Date Recue/Date Received 2020-11-02
[0017] FIG. 6 is a line graph illustrating corresponding profiles of
electricity usage in
a power supply system and electricity usage for intermittent heating of the
production
zone in an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0018] Selected embodiments of the present disclosure relate to methods of
hydrocarbon recovery from a reservoir of bituminous sands assisted by
injection of
steam and solvent as mobilizing agents into the reservoir (referred to as
steam-solvent
recovery processes), and methods of controlling injection of steam and solvent
into the
reservoir in such processes.
[0019] In overview, it has been recognized by the present inventor(s) that
an
improved recovery outcome may be achieved by adjusting the steam injection
rate
based on the real time temperature fluctuation in the solvent storage
temperature, in
comparison to injecting the steam at a constant rate that is determined based
on the
desired solvent to steam ratio in the injection mixture. In particular, it is
expected that
in an embodiment disclosed herein comparable recovery performance, e.g.,
instant or
cumulative oil or hydrocarbon production rates or both may be achieved at a
reduced
amount of overall steam injection.
[0020] Reducing the amount of injected steam not only can reduce
operational
costs associated with heating, storage, transportation, and injection of
steam, but can
also have positive environmental effects due to reduced consumption energy and
reduced emission.
[0021] Another possible benefit is that, for a given oil production site
with a steam
generation plant having a limited steam generation capacity, where the total
amount or
rate of steam generation by the steam generation plant cannot exceed the
capacity of
the plant, if the steam usage for injection of the solvent is reduced, the
saved steam
6
Date Recue/Date Received 2020-11-02
may be redirected and used for other purposes or functions in the recover
process at
the same site. Thus, better steam utilization may be achieved with little or
no increase
in steam generation cost.
[0022] As used herein in various embodiments, the term "reservoir" refers
to a
subterranean or underground formation containing recoverable hydrocarbons
(oil); and
the term "reservoir of bituminous sands" refers to such a formation wherein at
least
some of the hydrocarbons are viscous or immobile in their native state, and
are
disposed between or attached to sands.
[0023] In various embodiments, the terms "oil", "hydrocarbons" or
"hydrocarbon"
relate to mixtures of varying compositions comprising hydrocarbons in the
gaseous,
liquid or solid states, which may be in combination with other fluids (liquids
and gases)
that are not hydrocarbons. For example, "viscous hydrocarbons", "heavy oil",
"extra
heavy oil", and "bitumen" refer to hydrocarbons occurring in semi-solid or
solid form
and having a viscosity in the range of about 1,000 to over 1,000,000
centipoise (mPa.s
or cP) measured at the native in situ reservoir temperature. In this
specification, the
terms "hydrocarbons", "oil", and "bitumen" may be used interchangeably unless
otherwise specified. Depending on the in situ density and viscosity of the
hydrocarbons, the hydrocarbons may include, for example, a combination of oil,
heavy
oil, extra heavy oil, and bitumen. The term "oil" when used generally may
include "light"
oil, hydrocarbons mobile at typical reservoir conditions. Heavy crude oil, for
example,
may include any liquid petroleum hydrocarbon having an American Petroleum
Institute
(API) Gravity of less than about 20 such as lower than 6 , and a viscosity
greater than
1,000 mPa.s. Extra heavy oil, for example, may have a viscosity of over 10,000
mPa.s
and about 10 API Gravity. The API Gravity of bitumen typically ranges from
about 12
to about 6 or about 7 and the viscosity of bitumen is typically greater than
about
1,000,000 mPa.s.
[0024] The term "solvent" is also used herein in the broad sense. A
suitable solvent
may be propane or butane. Other solvents may also be used in different
embodiments.
Suitable solvents may also include diluents or condensates, such as natural
gas
7
Date Recue/Date Received 2020-11-02
condensates or natural gas liquids. The diluent may be selected from diluents
suitable
for use as additives to the produced hydrocarbons to facilitate transportation
of the
produced hydrocarbons by pipeline. The condensates may include condensates
produced from the same reservoir formation or a different reservoir formation,
and thus
may also be readily available on site. Suitable solvents may include
hydrocarbons
such as, propane, butane, pentane, or hexane, or heavier hydrocarbons. A
combination of solvents may also be suitable in some embodiments.
[0025] An example embodiment of the present disclosure relates to a steam-
solvent recovery for recovering hydrocarbons from a subterranean reservoir as
illustrated in FIG. 1.
[0026] FIG. 1 schematically illustrates a typical well pair configuration
in a
hydrocarbon reservoir formation 100, which can be operated to implement an
embodiment of the present disclosure. The well pair may be configured and
arranged
similar to a typical well pair configuration for steam-assisted-gravity-
drainage (SAGD)
operations, or a conventional steam-solvent recovery process.
[0027] The reservoir formation 100 contains viscous or heavy hydrocarbons
below
an overburden 110. Under the native conditions before any treatment, a
reservoir of
bituminous sands is typically at a relatively low temperature, such as about
12 C, and
the formation pressure may be from about 0.1 to about 4 MPa, depending on the
location and other characteristics of the reservoir.
[0028] The overburden 110 may be a cap layer or cap rock. Overburden 110 may
be formed of a layer of impermeable material such as clay or shale. A region
in the
formation 100 just below and near overburden 110 may be considered as an
interface
region.
[0029] In example embodiments, the well pair includes an injection well 120
and a
production well 130, which have horizontal sections extending substantially
horizontally in reservoir formation 100, and are drilled and completed for
producing
hydrocarbons from reservoir formation 100. Wells 120 and 130 may be configured
and
8
Date Recue/Date Received 2020-11-02
completed according to any suitable techniques for configuring and completing
horizontal in situ wells known to those skilled in the art. Injection well 120
and
production well 130 may also be referred to as the "injector" and "producer",
respectively.
[0030] As illustrated, wells 120 and 130 are connected to respective
corresponding
surface facilities, which typically include an injection surface facility 140
and a
production surface facility 150. Surface facility 140 is configured and
operated to
supply injection fluids, including steam and at least one solvent, into
injection well 120,
and will be further described in more detail below. Surface facility 150 is
configured
and operated to produce fluids collected in production well 130 to the
surface. Each of
surface facilities 140, 150 includes one or more fluid pipes or tubing for
fluid
communication with the respective well 120 or 130.
[0031] As better illustrated in FIG. 2, the surface facility 140 includes a
steam
source such as a steam generation plant 402, and a supply line such as fluid
pipe 404
connected to the steam generation plant 402 for supplying steam to injection
well 120
for injection into the reservoir formation 100. A fluid flow regulator such as
a valve 406
is provided in the fluid pipe 404 for regulating the fluid flow rate in the
fluid pipe 404.
Devices and equipment for driving steam flow and measuring steam properties
such
as steam temperature and pressure may be provided in the steam generation
plant
402 or along pipe 404, but for simplicity these devices and equipment are not
shown in
FIG. 2, as details of these devices and equipment are not necessary for
understanding
the present disclosure. For illustration purposes only, a flow meter 408 may
be
provided in the steam supply line, such as at fluid pipe 404 as depicted in
FIG. 2, for
measuring the steam flow rate in the steam supply line.
[0032] The surface facility 140 also includes a solvent source such as a
solvent
storage tank 412 and a supply line such as fluid pipe 414 for supplying the
solvent to
the injection well 120 for co-injection with steam. A flow regulator such as a
valve 416
is provided in pipe 414 for regulating the fluid flow in pipe 414. A flow
meter 418 is also
9
Date Recue/Date Received 2020-11-02
provided to measure the fluid flow rate through pipe 414. Optionally, a pump
420 is
provided to drive the fluid flow in pipe 414.
[0033] Valves 406, 416 may be any suitable fluid flow control valves for
use under
the particular operation conditions in a given embodiment. Existing valves
used in
steam and solvent supply lines in conventional steam-solvent recovery
processes may
be used. Valves 406 and 416 may be of the same type or be different, and may
be
selected so that valve 406 is suitable for controlling steam flow at the
expected steam
temperature and pressure ranges, and valve 416 is suitable for controlling
flow of the
particular solvent to be used.
[0034] Flow meters 408 and 418 may be any suitable fluid flow meters. They
may
be the same or of different types and measurement ranges selected for the
particular
application.
[0035] Optionally, surface facility 140 may include a heating facility (not
separately
shown) for pre-heating the solvent before injection.
[0036] Heating devices or heat insulation (not separately shown) may also
be
provided in one or more of the supply lines (e.g. pipes 404 and 414) for
control or
maintain the temperatures of the supplied fluids such as steam and solvents.
[0037] Both pipes 404 and 414 are connected to a mixing junction 422, which
is
connected to the injection well 120 through an input pipe 424, for mixing the
steam
and solvent before the mixture of steam and the solvent is injected into the
reservoir
formation 120.
[0038] As depicted, the mixing junction 422 is located at surface. However,
in
different embodiments, the mixing junction 422 may be located at surface, near
or in
the well head of injection well 120, or inside a section of the injection well
120. The
input pipe 424 may be a separate pipe connected to the injection well, or may
be a
part of the injection well 210.
Date Recue/Date Received 2020-11-02
[0039] A temperature sensor 426 may be provided at the mixing junction 422 or
downstream of the mixing junction 422 along the input pipe 424 for measuring
the
temperature in the mixture of steam and the solvent to be injected.
Temperature
sensor 426 is selected and located to measure the temperature in the
steam/solvent
mixture in the mixing junction 422 or in the input pipe 424 near the mixing
junction 422.
[0040] A temperature sensor 428 is also provided at the solvent storage,
such as
tank 412, for measuring the solvent storage temperature in real time.
Temperature 428
may be located at any suitable location in or adjacent tank 412 for measuring
the
storage temperature of the solvent. In an alternative embodiment, a
temperature
sensor such as sensor 418 may be provided in or along pipe 414 for measuring
the
solvent temperature before mixing.
[0041] The temperature sensors 426 and 428 may be any suitable sensors for
detecting and measuring the fluid temperatures at the expected temperature
ranges
and pressures for the respective fluids (solvent or mixture of steam and
solvent). For
example, the temperature sensors may be selected from thermocouples,
resistance
temperature detectors (RTD), thermistors, thermometers, infrared temperature
sensors,
digital temperature sensors such as semiconductor based temperature sensing
integrated circuit (IC), and the like.
[0042] When the mixing junction 422 is located downhole in the injection
well 120,
a distributed temperature sensing (DTS) device may also be used to detect the
temperature or temperature changes in the mixture of steam and the solvent.
[0043] Optionally, one or more additional supply lines may be provided for
supplying other fluids, additives or the like for co-injection with steam or
the solvent.
[0044] While not expressly depicted, it should be understood that each
supply line
may be connected to a corresponding source of supply, which may include, for
example, a boiler, a fluid mixing plant, a fluid treatment plant, a truck, a
fluid tank, or
the like. In some embodiments, co-injected fluids or materials may be pre-
mixed
11
Date Recue/Date Received 2020-11-02
before injection. In other embodiments, co-injected fluids may be separately
supplied
into injection well 120.
[0045] Surface facility 150 may include a fluid transport pipeline for
conveying
produced fluids to a downstream facility (not shown) for processing or
treatment.
Surface facility 150 also includes necessary and optional equipment (not
separately
shown) for producing fluids from production well 130, as can be understood by
those
skilled in the art.
[0046] Other necessary or optional surface facilities 160 may also be
provided, as
can be understood by those skilled in the art. For example, surface facilities
160 may
include one or more of a pre-injection treatment facility for treating a
material to be
injected into the formation, a post-production treatment facility for treating
a produced
material, a control or data processing system for controlling the production
operation
or for processing collected operational data.
[0047] Surface facilities 140, 150 and 160 may also include recycling
facilities for
separating, treating, and heating various fluid components from a recovered or
produced reservoir fluid. For example, the recycling facilities may include
facilities for
recycling water and solvents from produced reservoir fluids.
[0048] Injection well 120 and production well 130 may be configured and
completed
in any suitable manner as can be understood or is known to those skilled in
the art, so
long as the wells are compatible with injection, and optionally recovery, of a
selected
solvent to be used in a steam-solvent recovery process as will be disclosed
below.
[0049] For example, in different embodiments, the well completions may
include
perforations, slotted liner, screens, outflow control devices such as in an
injection well,
inflow control devices such as in a production well, or a combination thereof
known to
one skilled in the art.
[0050] FIG. 1 shows wells 120, 130 in formation 100 during a recovery
process
where a vapour chamber 360 has formed.
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Date Recue/Date Received 2020-11-02
[0051] As illustrated, each of injection well 120 and production well 130
has a
casing 220, 230 respectively. An injector tubing may be positioned in injector
casing
220 and connected to input pipe 424 for receiving the mixture of steam and the
solvent
to be injected into the reservoir formation 100. The use of the injector
tubing can be
understood by those skilled in the art, and will be described below.
[0052] For simplicity, other necessary or optional components, tools or
equipment
that are installed in the wells are not shown in the drawings as they are not
particularly
relevant to the present disclosure.
[0053] In operation, wells 120 and 130 may be operated to produce
hydrocarbons
from reservoir formation 100 according to a process disclosed herein.
[0054] For example, in an embodiment the wells 120 and 130 may be initially
operated as in a conventional SAGD process, or a suitable variation thereof,
as can be
understood by those skilled in the art. In this initial process, steam may be
the only or
the dominant injection fluid.
[0055] Alternatively, steam and a solvent may be co-injected at the start
of the
production stage after the start-up stage.
[0056] In any event, both steam and one or more solvents are injected
during at
least one period of the production stage, and the following description is
focused on
such injection period. Optionally, a non-condensable gas such as methane may
also
be injected with the steam and the solvent.
[0057] Steam is supplied by steam generator 402 to junction 422 through
pipe 404,
and a solvent such as propane is supplied by solvent tank 412 to junction 422
through
pipe 414, as illustrated in FIG. 2. The steam flow may be driven by steam
generator
402 and regulated by valve 406. The steam flow rate may be measured using flow
meter 408. The solvent flow may be driven by pump 420 and regulated by both
valve
416 and pump 420. The solvent may be supplied to junction 422 in the liquid
phase or
gas phase, or in both phases. The solvent may be compressed during storage. In
an
embodiment, the solvent may be supplied to pipe 414 as a liquid. In a
different
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Date Recue/Date Received 2020-11-02
embodiment, the solvent may be stored in a liquid state and supplied to pipe
414 as a
vapor, or heated and vaporized in pipe 414 before the solvent is supplied to
junction
422. The solvent flow rate is measured by flow meter 418. The solvent
temperature
(Ts01) is detected by temperature sensor 428. The temperature (Tm) in the
mixed
stream and solvent after junction 422 is detected by temperature sensor 426.
[0058] For steam-solvent co-injection, at given injection temperature and
pressure
of the injected mixture, and given expected average solvent storage
temperature and
steam supply conditions (including steam temperature, pressure and quality),
the initial
or base solvent injection rate and steam injection rate may be determined.
[0059] Determination of the base injection rates may be based on a selected
solvent-to-steam ratio in the injection stream in pipe 414 for optimal
production
performance or other considerations, as can be understood by those skilled in
the art.
For example, a target solvent to steam ratio may be selected according to the
techniques disclosed in CA 3,027,274. The target solvent to steam ratio may be
determined in consideration of a number of factors as will be understood by
those
skilled in the art, and further explained below.
[0060] For a given solvent to steam ratio, a corresponding target
temperature, Tt, in
the injection stream (mixture) in pipe 424 can also be determined. It is noted
that the
actual temperature in the injection stream (mixture) in pipe 424 may vary over
time and
is not necessarily the same as the target temperature Tt at any given time.
[0061] As some flow characteristics and thermodynamic properties of steam
and
solvent flows in pipe 404 and 414 can affect the dependency of lion the target
solvent
to steam ratio, the actual relevant flow characteristics and thermodynamic
properties of
steam and the solvent may also be determined or obtained. For example, the
steam
temperature and pressure and steam quality may be measured or already known
based on information obtained from the steam generation process at steam
generator
402. It is also possible to measure actual steam temperature and pressure in
pipe 404
using suitable temperature and pressure sensors (not shown) installed in pipe
404.
14
Date Recue/Date Received 2020-11-02
[0062] The solvent temperature may be determined based on the storage
temperature of the solvent in storage tank 412 as detected by temperature
sensor 428.
The solvent pressure may also be determined or measured based on the storage
pressure of the solvent in storage tank 412 or the pump pressure at pump 420,
depending on the situation, using a pressure sensor (not shown). The pressure
of the
solvent may also be determined based on the solvent temperature without
directly
measurement using a pressure sensor.
[0063] In different embodiments, the solvent temperature and pressure may
also be
measured in pipe 414 using suitable sensors (not shown).
[0064] The flow rate of the solvent stream in pipe 414 can be directly
measured
using flow rate meter 418.
[0065] Some of these quantities or operation parameters may be obtained based
on estimation or modeling and do not need to be directly measured in some
embodiments. For example, the flow rate or pressure of the solvent may be
estimated
based on the pumping speed of pump 420.
[0066] For illustration purposes only, in a simple case, the temperature of
a mixture
of two fluids may be calculated as follows in Equation (1), assuming there is
no phase
change (e.g., no evaporation or condensation) and no other net energy
loss/gain in the
system during mixing:
Tfinal = M1 C1 T1 + 1772 C2 T2, (1)
where "mi" represents the mass of each input fluid "i", "c" represents the
specific heat
of the input fluid, Ti"" represents the temperature of the input fluid
before it is mixed
with the other fluid, and "7-final" is the temperature of the mixture of the
two fluids.
[0067] The solvent to steam ratio in a mixture of steam and solvent may be
calculated by mseiven / t. Msteam , where mseivent and Msteam are the masses
of solvent and
steam in the mixture respectively, or by rseivent/rsteam, where rseivent and
rsteam are the
injection rates of solvent and steam respectively. Equation (1) may be thus
rewritten as
Date Recue/Date Received 2020-11-02
Equation (2) to provide the relation between the target mixture temperature
and the
selected solvent to steam ratio:
Tr = grsolvent/rsteam) ci Ti + C2 T23 rSteaM
= [(solvent to steam ratio) ci Ti + c2 T2,) rsteam. (2)
[0068] The relationship or correlation between the temperatures and the
target
solvent to steam ratio can be more complicated in practice, such as when more
fluids
are involved, or in non-ideal situations such as when there is heat loss/gain
or phase
change during mixture.
[0069] The more complicated relationships can be determined using models or
using known techniques, including computer modeling software products
commercially
available.
[0070] As can be appreciated by those skilled in the art, the target
temperature Tt at
temperature sensor 426 can be determined based on the target solvent to steam
ratio,
and the relevant flow and thermodynamic characteristics and properties
determined/obtained as described above. For example, a person skilled in the
art
would understand how to calculate the target temperature Tt for a given
solvent to
steam ratio (on the basis of weight, volume, or molar percentages) and the
relevant
flow and thermodynamic information of the input streams. For example, the
temperature of the mixture may be affected by the temperatures of the input
steam
and solvent, the solvent to steam ratio (or in weight/molar percentages of the
solvent)
in the mixture, the steam quality and the phase(s) of the input solvent and
the phase(s)
of the solvent in the mixture. As can be understood, the solvent to steam
ratio is
directly dependent on the flow rates of input steam and solvent.
[0071] The target temperature Tt may be previously known, and may be a
constant
over a period of time, but may also be dynamically determined in real time
from time to
16
Date Recue/Date Received 2020-11-02
time, continuously, at regular intervals, or periodically based on detected or
other input
values that may fluctuate or change over time.
[0072] For example, the injection temperature may be selected in part based
on the
selected solvent and its thermodynamic properties and the target pressure in
the
injection stream. For instance, in some embodiments, gaseous propane may be
injected, as a minimum criteria, at 2 MPa and 60 C or 70 C, or at 3 MPa and
80
C. When the steam pressure is 3.1 MPa with the temperature of 303 C, and the
downhole pressure is 3.2 MPa, propane may be injected at an injection rate of
1.3 t/hr
and steam may be injected at an injection rate of 2.17 t/hr, with the overall
mixture
temperature of 185 C.
[0073] It is also possible to determine the correlation between the steam
flow rate R
in pipe 404 and the temperature (T) in pipe 414 based on the known flow and
thermodynamic characteristics/properties of the input streams. This
correlation may be
calculated based on a theoretical or a simulation model, or may be empirically
determined based on experimental or field data, or may be based on both. For
example, the correlation may be completely based on calculation using known
flow
dynamic and thermodynamic relationships and measured input data. The
correlation
may be completely based on testing using direct flow rate measurements under
the
same or similar flow and thermodynamic conditions. Some correlation
information may
be extrapolated from calculations or testing data for higher or lower flow
rates.
[0074] For a given target solvent to steam ratio, the target temperature Tt
and
target steam flow rate (Rt) corresponding to the target solvent to steam ratio
can be
determined based on the correlation.
[0075] The flow rate of the input steam stream and the flow rate of the
input solvent
stream can be separately measured using flow meters 408 and 418 installed in
the
input pipes 404 and 414 respectively, and can be regulated or controlled using
flow
valves 406 and 416 to achieved the selected or desired rates. The flow rates
may be
manually controlled based on the flow meter readings, or may be automatically
controlled. In some embodiments, a flow rate in one of the supply lines may be
17
Date Recue/Date Received 2020-11-02
estimated or determined without using a flow meter in the supply line. For
example, the
flow rate may be estimated based on the correlation between the flow rates and
the
temperatures of the input steams and the temperature of the injection stream
of the
mixed steam and solvent.
[0076] Optionally, a correlation between the temperature in pipe 414 as
detected by
sensor 426 (T) and the steam flow rate (R) in pipe 404 may be obtained or
determined.
[0077] This correlation between T and R may be already known to the operator,
may be pre-determined once before or during the control process, or may be
determined repeatedly during control process, as will be further discussed
below. The
correlation may be expressed as a formula (e.g. R = f (T), where "f'
represents a
mathematical function), a correlation (mapping) table or the like, and may be
presented to the operator by any visual devices or calculated by a computer in
real-
time using an algorithm or routine.
[0078] For example, the correlation between T and R may be determined based
on
the relevant flow and thermodynamic characteristics of the steam flow and
solvent flow
in pipes 404 and 414. Relevant flow and thermodynamic characteristics of a
flow may
include the temperature, pressure, and flow rate, as wells the phase state or
quality of
the fluid (e.g. vapor or liquid). For a flow of saturated steam, the steam
quality is
relevant in this context as the steam quality is related to the total enthalpy
of the steam
stream and can affect the heat transfer and resulting temperature in the steam-
solvent
mixture after the steam and solvent is mixed. Steam quality refers to the
proportion of
steam (vapor) in a saturated mixture of steam (vapor) and condensate water
(liquid).
[0079] Steam and the solvent can be continuously supplied to pipe 424 at
junction
422 at the selected solvent flow rate and an initial steam flow rate, which
may be
typically below or slightly higher than the target or base steam flow rate
(Rt), and the
actual mixture temperature Ta in pipe 424 is detected at sensor 426.
18
Date Recue/Date Received 2020-11-02
[0080] When the solvent temperature and solvent injection rate remain
constant
over time, the steam flow rate R in pipe 404 may be adjusted based on the
detected
Ta, and the target temperature Tr. For example, the difference (AT) between
the
detected temperature Ta and the target temperature Tt in pipe 424 may be
calculated
as AT = Ta ¨ Tt. If AT < 0, more steam is required to reach the base target
temperature
Tt to provide the target solvent to steam ratio, the steam flow rate R in pipe
404 is
increased by opening up the flow valve 406. If AT> 0, less steam is required
to
provide the target solvent to steam ratio, the steam flow rate R in pipe 404
is
decreased by closing down the flow valve 406. If LIT= 0, or when AT is within
an
acceptable range, the steam flow rate does not need to be adjusted, and the
steam
flow rate R in pipe 404 may be maintained at a constant level, i.e., at the
target
temperature. In practice, the temperature response to the steam flow rate
adjustment
may not be instantaneous, and a delay time may be required after any
adjustment of
the steam flow before the temperature T in pipe 424 is stabilized. For more
accurate
flow adjustments, A T should be calculated based on Ta detected at a time when
the
temperature Tin pipe 424 is substantially stable. The above adjustment may be
repeated until the co-injection operation is terminated or suspended, or the
control
process is no longer needed in the recovery process.
[0081] As can be appreciated by those skilled in the art, when the steam
flow rate R
is adjusted to provide the target temperature Tt, it is expected that the
solvent to steam
ratio in the injection stream in pipe 424 should be the corresponding target
solvent to
steam ratio, or is close to the target solvent to steam ratio within an
acceptable
tolerance range. Therefore, the above process in effect adjusts the steam flow
rate R
to reach the target solvent to steam ratio based on the detected Ta, provided
that the
correlation between R and solvent to steam ratio as reflected through Tt and
the
correlation between the mixture temperature and the steam flow rate, including
the
solvent storage (injection) temperature, remain substantially unchanged over
the
period of injection.
[0082] However, in practice, the solvent storage temperature may not remain
substantially constant over a long period of time. For example, significant
temperature
19
Date Recue/Date Received 2020-11-02
fluctuation in the solvent storage may occur due to the normal cycles of sun
set and
sun rise over days, and due to seasonal temperature changes on earth at the
storage
location.
[0083] FIG. 3 shows a representative temperature profile in a solvent
storage tank
over time (about a week) and the corresponding environment temperature
profile. The
storage tank was not temperature controlled, so the solvent storage
temperature
fluctuates over time with the local environmental temperature and any
radiation
heating from sunlight, which went through the normal daily cycles.
[0084] As can be seen from FIG. 3, in this particular case, the solvent
storage
temperature can increase or decrease significantly, by about 15 to 18 C over
a day,
and more over the time of a week.
[0085] In this case, if the steam injection rate is kept constant for the
selected Tt,
based on an expected input solvent temperature of, say, 45 C, the same steam
injection rate would not be sufficient to achieve the Tt during the night or
early morning
when the solvent temperature is below about 40 C, but would be too high in
the
afternoon when the solvent temperature is above about 50 C. That is, in the
early
morning, insufficient heat energy is provided by the steam, and production
performance may be negatively affected; but in the afternoon, an oversupply of
heat
energy is provided by the steam, which may not cost-effectively increase
production
performance.
[0086] This effect is illustrated in FIG. 4, where the corresponding
temperature of
the mixture of steam/solvent also fluctuated when the solvent and steam
injection
rates were kept constant. The general trend of the change in the mixture
temperature
correspond to the change in the solvent temperature. Additional minor
fluctuations in
the mixture temperature seen in FIG. 4 may be due to relatively small changes
in the
steam supply.
[0087] If the steam injection rate was to be adjusted merely based on the
detected
Ta to maintain the target temperature Tr, it would not provide the desired
target solvent
Date Recue/Date Received 2020-11-02
to steam ratio over the period of one day, as in the early morning more steam
would
be required so the solvent to steam ratio in the early morning is lower than
the target
solvent to steam ratio and in the afternoon less steam would be required so
the
solvent to steam ratio in the afternoon is higher than the expected value. In
either
case, the optimal performance may not be achieved.
[0088] Instead, improved or optimal performance can be achieved according
to an
embodiment of the present disclosure by taking into account of the real time
fluctuation
of the solvent temperature, where the steam injection rate is decreased when
the
solvent temperature is higher than the base solvent temperature used to
determine the
Tr, and is increased when the solvent temperature is lower than the base
solvent
temperature, to compensate for the real time fluctuation in the input solvent
temperature.
[0089] Considered in an alternative way, in an embodiment of the present
disclosure, the goal of adjusting steam flow rate is not to maintain constant
the solvent
to steam ratio at a target value or to change the target temperature in the
mixture, but
to maintain the mixture temperature at a selected value such as a target value
that
has already been reached, in which case the steam flow rate may be adjusted
over
time in synchronization with the solvent temperature fluctuation, so that the
steam
injection rate is higher when the solvent temperature is lower and the steam
injection
rate is lower when the solvent temperature is higher, to compensate for the
heat
energy the solvent absorbed from or lost to the environment, such as due to
the cyclic
nature of sunlight.
[0090] In further embodiments, additional measures may be taken to account
for
factors that can affect the solvent storage temperature, or take advantages of
the
environmental temperature changes or solar energy changes.
[0091] For example, to reduce loss of heat energy from the solvent tank 412
to the
environment, and to increase absorption of solar energy from sunlight into the
solvent
stored in the solvent tank 412, the exterior of the solvent tank 412 may be
painted a
dark color such as black. Thermal insulation may be provided outside the tank
412
21
Date Recue/Date Received 2020-11-02
during the winter season, or when the temperature is lower than a certain
threshold,
and light absorbing materials may be used to absorb sunlight during the day.
[0092] A solvent storage container may also be otherwise coated with a
light
absorbing coating to increase heat energy absorbed by the container from the
sunlight, for increasing the temperature of the stored solvent.
[0093] In alternative embodiments, solar panels may be used to store
thermal
energy during the day and provide the stored energy to the stored solvent
during the
night, such that the temperature fluctuation in the storage tank is reduced
over the
period of a day.
[0094] The injection rates may be regulated and controlled manually,
automatically,
or semi-automatically. For example, a control system such as the system 500
illustrated in FIG. 5 may be used to control the injection rates.
[0095] As depicted, system 500 includes a controller 502, which may be
connected
to steam generator 402, valve 406, pump 420, valve 416, flow meter 418 and
temperature sensors 426 and 428, for controlling the operation of valves 406,
416, and
optionally steam generator 402. Controller 502 may optionally be connected to
input
devices or sensors (not shown) that can provide data or signal indicative of
the
properties of the solvent, such as pressure and other information, stored in
solvent
tank 412. The connection between any two devices may be wired or wireless, and
may
be direct or through one or more intermediate communication or control
devices, as
can be understood by those skilled in the art.
[0096] Controller 502 may include one or more processors such as
microprocessors or computing units such as one or more central processing
units
(CPU) or specialized processing circuits units. In some embodiments, a general
purpose computer may be used, and is specifically configured and programed to
perform the some of the functions and methods described herein.
[0097] For example, in some embodiments, system 500 may include a PID
(proportional integral derivative) controller for controlling temperature,
which is
22
Date Recue/Date Received 2020-11-02
connected to sensors 426 and 428 to receive the respective detected
temperatures as
feedback input, and outputs a control signal to close or open valve 406 as the
control
element. The target temperature values of Tt may be determined by a processor
in
controller 502 in real time based on the detected solvent storage temperature
from
sensor 428, or may be pre-set to vary according to a time-dependent formula or
table.
[0098] The
PID may be a digital PID or analog PID. In other embodiments, a PD
(proportional-derivative) or PI (proportional-integrated) controller may be
used to
control the valve 406 based on the detected temperature, depending on the
particular
application.
[0099] In
some embodiments, a programmable controller such as programmable
logic controller (PLC) may be included in system 500. A programmable
automation
controller (PAC) may also be included in system 500.
[00100] In
some embodiments, system 500 may be configured as a distributed
control system (DCS), and may include a supervisory control computer and a
number
of controller or control units.
[00101] System 500 may also be configured to provide advanced process
control
(APC). For example, system 500 may be configured to provide multivariable
model
predictive control (MPC), including nonlinear MPC. The APC system may be based
in
part on inferential measurements of some variables, such as one or more of the
temperature and pressure of steam in pipe 404, the temperature of the solvent
in pipe
414, and the flow rate of the solvent in pipe 414.
[00102]
System 500 may be configured to provide continuous control of valve
406. It is also possible in some embodiments that system 500 is configured and
programmed to provide sequential control where valve 406 is controlled and
adjusted
in time- or event-based automation sequences. For example, a triggering event
for an
automated control sequence may be a change, either detected or expected based
on
historical data, in the input solvent temperature due to environmental
condition (e.g.
temperature or sunlight) fluctuations or process. Other changes may also
trigger a
23
Date Recue/Date Received 2020-11-02
control sequence, including a change in injection condition (such as those
dictated by
recovery process considerations), a change in the solvent supply (e.g., batch
change,
truck change, flow rate change or the like), a change in the steam supply
(e.g., a
temperature or pressure change, or a change in steam quality), or the like. An
automated control sequence may also be started at pre-defined times, or after
a given
time interval, or at regular time intervals, for example to account for daily
or seasonal
sunlight changes.
[00103] System 500 and controller 502 may also be configured and
programmed
to provide simulation-based control or optimization of the control of valve
406 for
controlling the steam injection rate R.
[00104] Suitable controllers may include controller or control systems
configured
to run, and installed with, suitable simulation software, such as software
available from
HoneywellTM under the brand name UNISIMTm.
[00105] One or more reservoir simulation algorithms or software with fluid
transport and heat transfer calculations may be used to provide used to
provide
needed information for control.
[00106] As depicted in FIG. 5, system 500 may also include a computer or
processor readable storage media, such as memory 504, for storing both
processor
executable instructions and data needed to perform the injection control
process and
optionally other functions or tasks. Memory 504 may include any suitable
computer
memory devices or storage devices. In particular, memory 504 may store thereon
processor executable instructions, which when executed by a processor causes
controller 502 to perform the control process.
[00107] System 500 may further include input/output (I/O) interface
devices,
communication devices (not separately shown) for communication with other
connected devices, and for receiving input from a user and for outputting
control
signals or presenting information to the user.
[00108] In particular, during operation, control system 500 may receive
input from
24
Date Recue/Date Received 2020-11-02
a user for determining the target injection temperature Tt. Control system 500
may also
communicate with the steam generator 402 or devices associated with the steam
generator 402 to obtain operation parameters and information about the input
steam,
such as its temperature, pressure, steam quality, and the like.
[00109] Controller 502 may also be connected to input devices or sensors
such
as temperature sensor 428 or flow meter 418, which are associated with the
solvent
source or a solvent transportation line, such as the solvent tank 412 or pipe
line 414.
Controller 502 may receive data or signal indicative of the properties of the
solvent,
including its temperature and optionally other information, stored in the
solvent source
such as solvent tank 412, or the transported through the transportation line
such as
pipe line 414. Alternatively, such information about the solvent may be input
by a user
or operator.
[00110] Control system 500 may further communicate with flow meter 408,
or
optionally steam generator 402, to obtain the flow rate of the solvent stream
in pipe
404.
[00111] Control system 500 may further communicate with flow meter 418,
or
optionally pump 420, to obtain the flow rate of the solvent stream in pipe
414.
[00112] Control system 500 may communicate with temperature sensors 426
and
428 directly or indirectly, through wired or wireless connections, to receive
the
temperature feedback from temperature sensors 426 and 428. Control system 500
may receive a digital or analogue signal from temperature sensors 426 and 428.
[00113] Optionally, control system 500 may be configured and programmed
to
receive an input of the target solvent to steam ratio, and in response to
receiving the
target solvent to steam ratio, determine the corresponding base target Tt in
pipe 424
based on the target solvent to steam ratio and the current flow and
thermodynamic
parameters and characteristics, such as by calculation or by searching a data
structure
(e.g. mapping table) stored in system 500. Optionally, system 500 may be
configured
and programmed to receive an input from a user or another device that
indicates the
Date Recue/Date Received 2020-11-02
base target Tt. Control system 500 may be further configured and programmed to
adjust target Tt based on historical information or detected temperatures to
account for
real time fluctuations in the solvent storage temperature.
[00114] System 500 may be configured and programmed to determine a
dynamic
correlation between the steam flow rate in pipe 404 and the temperature in
pipe 414
based on stored information including the flow and thermodynamic parameters
and
characteristics described herein, and the time-dependent solvent temperature.
[00115] During operation, system 500 may control the steam flow rate in
pipeline
404, such as by adjusting the valve 406, or the pumping speed of a pump (not
shown)
either located along pipeline 404 or at steam generator 402, based on the
detected or
expected temperature fluctuation in the stored solvent at tank 412. For
example,
controller 502 may process temperature signals from sensor 428 and adjust the
valve
406 to regulate the steam flow rate in pipeline 404 so that the mixture
temperature at
line 424 is stable at or close to the selected target temperature Tt over
time, even
when the solvent temperature fluctuates due to changes in the environmental
conditions. Alternatively, controller 502 may access stored data on memory 504
to
predict the expected solvent temperature in tank 402, and adjust the valve 406
to
regulate the steam flow rate in pipeline 404 accordingly.
[00116] In some embodiments, the mixture temperature Tt may optionally
vary or
be adjusted, such as to provide improved or optimal performance results.
However, in
such cases, the steam flow rate is still adjusted to account for the real time
temperature fluctuations in the input solvent stream, so as to reduce
unnecessary or
less efficient steam usage.
[00117] In a further embodiment, the base solvent to steam ratio may be
determined based on the expected solvent temperature, which may be referred to
as
the reference or base solvent temperature. However, since the solvent to steam
ratio
may be different at different solvent input temperatures, the actual target
solvent to
steam ratio may be adjusted in view of the actual solvent temperature, and the
steam
flow rate or the solvent flow rate may be adjusted to maintain the solvent to
steam ratio
26
Date Recue/Date Received 2020-11-02
at the optimal value that corresponds to the actual solvent temperature in
real time,
instead of maintaining the solvent to steam ratio at the fixed value of the
base solvent
to steam ratio determined based on the reference/base solvent temperature.
[00118] In an example, assume that the solvent may be injected at a rate
of 40
lid and the steam may be injected at a rate of 26 t/d to achieve a target
mixture
temperature of 190 C, and that when the solvent is pre-heated by solar
radiation and
the solvent and steam are still injected at the same rates, the mixture
temperature may
reach 200 C. Then, with the pre-heated solvent, it is possible to reduce the
steam
injection rate to lower the mixture temperature back to 190 C. The steam
injection
rate may be reduced incrementally, e.g., by 0.1 t/hr at each iteration. The
mixture
temperature may be monitored and the steam injection rate may be automatically
or
manually reduced by the selected increment until the mixture temperature
reaches the
target mixture temperature of 190 C.
[00119] In view of the above factors and considerations, once the solvent
has
been selected and the conditions of the input materials to the injection
stream have
been determined, the target injection temperature may be selected, or
optionally, the
base target solvent to steam ratio may be selected, according to the above
descriptions as can be understood by those skilled in the art.
[00120] When the correlation between the mixture temperature and the
steam
injection rate (such as a baseline rate or reference rates) is established for
given
injection conditions, e.g., by simulation, calibration, testing, or
combination thereof,
steam injection rate may be controlled based on the detected mixture
temperature and
the detected or expected solvent temperature, without determining or
calculating the
actual solvent to steam ratio (or any weight, volume, or molar percentage of
steam or
solvent) in the mixture.
[00121] In selected embodiments, the increase and decrease of the steam
injection rate may also be controlled taking into account of the electricity
costs at the
time. For example, when the steam generation and transport require electrical
power,
reducing the steam injection rate can reduce the instant electrical power
consumption.
27
Date Recue/Date Received 2020-11-02
[00122] It is common that the electricity usage in a power grid will
fluctuate over
time and have regular peak periods and off-peak periods. Typically, in peak
periods
when the general demand for electrical power is higher in a power supply
network, the
electricity cost will be higher, and in the off-peak periods when the demand
for
electrical power is lower, the electricity cost will be lower. Many utility
and electrical
power providers will charge a higher rate during the day when electrical power
consumption in the local region is higher and a lower rate from after mid-
night to early
morning when the electrical power consumption in the local region is lower.
[00123] Conveniently, when the steam injection rate is adjusted as
described
above in view of the daily fluctuation of the solvent storage temperature and
the
solvent storage temperature fluctuates mainly due to the daily cycle of the
sunlight and
environmental temperature changes, the steam injection rate is intermittently
increased and decreased over daily cycles, where the increased steam injection
rate
at late night and early morning can be less costly because of the reduced
electricity
cost at that time, and the decreased steam injection rate during the day can
also
reduce costs as at the time the electricity cost is relatively higher.
[00124] In some embodiments, the adjustment of the steam injection rate
may be
further timed to better synchronize with the daily electricity cost changes.
For example,
as schematically illustrated in FIG. 8, the steam injection rate (or the
overall electricity
consumption at the site) may have a profile that tracks or matches the peak
and off-
peak usage in the power source (e.g. a power grid in this depicted example).
In FIG. 8,
the bottom line represents the general electricity usage in a power grid,
where ti, t2, t3,
t4 and t5 represent different points in time, such as different times in a
day. It is also
assumed that different electricity costs or charge rates would apply depending
on the
electricity usage levels at the time. Accordingly, to optimize electricity
usage, the
steam injection rate, represented by the top line in FIG. 8, may have the
profile as
shown, to take advantage of the fluctuations of electricity cost over the day.
Such
changes in the steam injection may be referred to as intermittent injection.
[00125] In some embodiments, the input solvent may be heated before
injection
28
Date Recue/Date Received 2020-11-02
and the heating power used to heat the solvent may also be adjusted in view of
the
electricity cost fluctuations. In particular, the input solvent may be
subjected to
intermittent heating.
[00126] Such intermittent injection and intermittent heating may be more
economical and, when scheduled appropriately, may not negatively affect the
production performance significantly. The process may be, for example operated
intermittently so as to reduce or minimize the overall operating expenses
(OPEX)
associated with electricity usage for the recovery process, including steam
generation
and injection and any heating of the input materials or even direct electrical
heating in
the wells.
[00127] For example, the electricity cost to the operator of the recovery
process
may be substantially reduced during the off-peak period, as compared to the
peak
period. Cyclically alternating between increased injection/heating and reduced
injection/heating over 24 hour cycles as described herein may not
significantly affect
the injection temperature of the injected mixture and the average temperature
in the
reservoir.
[00128] Thus, an additional factor for selecting the injection rates and
injection
rate profiles may include the electricity costs at different time periods
during a day or
different days of the week or in different seasons.
[00129] As now can be appreciated, the embodiments described above may be
modified for application in different contexts or for more general
applications.
[00130] To further illustrate embodiments of the present disclosure, some
non-
limiting and representative examples are discussed below.
[00131] Examples
[00132] Example I
[00133] In a particular example, propane was used as the solvent and
injected
with steam into a well for recovery of oil from a bitumen reservoir.
29
Date Recue/Date Received 2020-11-02
[00134] At selected target injection conditions and assuming the solvent
would
be at room temperature, it was determined that the optimal steam injection
rate should
be 0.4 ton/hr when the propane injection rate was 1.7 ton/hr for injection at
3 MPa and
80 C.
[00135] However, during injection, it was observed that the resulting
mixture
temperature of steam and the solvent (Ta) were between about 113 C during the
minimum atmospheric temperature and about 121 C at the maximum atmospheric
temperature over the period of days in the summer, where the injection
pressure was
about 3.4 to about 3.7 MPa.
[00136] As noted earlier, propane may be injected at 2 MPa and 70 C, or
at 3
MPa and 80 C. However, due to solar radiation heating of the solvent tank,
the
solvent storage temperature fluctuated over the day as shown in FIG. 3, where
the
storage temperature of the propane dropped to about 40 C at the lowest point
and
rose to about 54 C at the highest point. Taking into consideration of these
fluctuations
of the solvent storage temperature, for injection at a pressure of 2 MPa, the
injection
propane will only need to be heated by 16 C at the storage temperature of 54
C as
compared to by 30 C at the storage temperature of 40 C, to reach the target
70 C.
For injection at the pressure of 3 MPa, the propane temperature would need to
be
increased by 26 C at the storage temperature of 54 C as compared to by 40 C
at
the storage temperature of 40 C, to reach the target 80 C. The steam
injection rate
could thus be reduced from about 1 ton/hr (at the lower solvent storage
temperature)
to about 0.4 ton/hr (at the higher storage temperature). The steam injection
rate might
be adjusted, such as further reduced, as long as the target temperature in the
injection
mixture of steam and solvent can be achieved.
[00137] The steam injection rate was thus controlled as follows.
[00138] For injection pressure of 3 MPa, the target injection temperature
(Tt) was
fixed as a constant at 80 C. Propane in the gas phase was mixed with steam.
Date Recue/Date Received 2020-11-02
[00139] The propane storage temperature is monitored, and the steam
injection
rate was increased when the propane temperature dropped over night, and was
decreased when the propane temperature rose during daylight. The steam
injection
rate was varied and regulated to maintain the target injection temperature Tt.
[00140] The steam injection rate increase and decrease were repeated each
day.
[00141] Less than 0.4 ton/hr injection rate was required to maintain the
target
temperature, and even less is required during daylight time.
[00142] CONCLUDING REMARKS
[00143] Various changes and modifications not expressly discussed herein
may
be apparent and may be made by those skilled in the art based on the present
disclosure.
[00144] It will be understood that any range of values herein is intended
to
specifically include any intermediate value or sub-range within the given
range, and all
such intermediate values and sub-ranges are individually and specifically
disclosed.
[00145] It will also be understood that the word "a" or "an" is intended
to mean
one or more" or at least one", and any singular form is intended to include
plurals
herein.
[00146] It will be further understood that the term "comprise", including
any
variation thereof, is intended to be open-ended and means "include, but not
limited to,"
unless otherwise specifically indicated to the contrary.
[00147] When a list of items is given herein with an "or" before the last
item, any
one of the listed items or any suitable combination of two or more of the
listed items
may be selected and used.
31
Date Recue/Date Received 2020-11-02
[00148] Of course, the above described embodiments are intended to be
illustrative only and in no way limiting. The described embodiments are
susceptible to
many modifications of form, arrangement of parts, details and order of
operation. The
invention, rather, is intended to encompass all such modification within its
scope, as
defined by the claims.
32
Date Recue/Date Received 2020-11-02
