Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR PRODUCING DE-WATERED OIL
Field
The present invention relates to a system for
producing de-watered oil from an underground formation.
Background
In the specification and in the claims, the
expression 'well fluidr will be used to refer to a fluid
comprising hydrocarbon oil and water that is received by
a system according to the present invention from an
underground formation. Further, hydrocarbon oil will be
referred to as oil.
The present invention relates in particular to a
system, wherein a well fluid can be separated
underground, such that oil is produced to the surface
that has been de-watered below the surface. It will be
understood, that the surface may also be the bottom of
the sea.
International patent application publication
No. WO 98/41304 discloses a system for producing oil from
an underground formation, which system comprises
- a production well extending downwardly from the
surface and having an inlet below the surface;
- a reception well penetrating the underground
formation and capable of receiving well flu"id therefrom,
wherein the downstream part of the reception well
comprises a substantially horizontal section; and
- a water discharge system having an upstream end that
is capable of receiving liquid from the lower region of
the horizontal section,
wherein the inlet of the production well is arranged
to receive liquid from the upper region of the horizontal
-section.
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During normal operation of the known system, the flow
of well fluid is selected such that the well fluid is
separated in the horizontal section. Liquid layers are
formed in the upper and lower regions of the horizontal
section, and an interface is formed between the layers.
Near the downstream end of the horizontal section the
liquid flowing in the lower region is a water-rich
component, and the liquid flowing in the upper region is
an oil-rich component of the well fluid. The oil-rich
component is produced to the surface, and the remaining
water-rich component is disposed. Optionally, the water-
rich phase is subjected to a further separation step.
The known system provides only bulk removal of water.
In order to obtain a substantially water-free oil having
a water concentration that is sufficiently low to allow
pipeline transport of the oil, the known system further
comprises an oil-water separator at the surface.
Furthermore it is disclosed in the publication, that for
this bulk removal of water the level of the interface
should be kept within narrow limits.
Not only is the known system directed to the bulk
removal of water, but it is also directed to getting a
low oil concentration in the water-rich component, and if
necessary this is done at the cost of a higher water
concentration of the produced oil.
Applicant has reviewed the separation behaviour of a
mixture of oil and water using a proprietary model. The
model calculations, of which results will be discussed
with reference to Figures 1 and 2 below, have revealed
that for realistic operation conditions in horizontal
wells (including flow rate of the well fluid, length and
diameter of the horizontal section), the concentration of
water in the oil-rich component is considerable. In
practice this will require de-watering of the produced
oil before it can be transported from the wellhead, e.g.
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through a pipeline.
In this regard it is observed, that unrealistic
operating conditions were used to arrive at the results
depicted in Figures 2 and 3 of the above-mentioned
International patent application.
UK Patent application No. GB 2 326 895 A discloses an
apparatus for producing fluid containing hydrocarbons and
water from an underground formation by using a single
underground separation step, in order to permit reduction
of the separation equipment at the surface. The apparatus
comprises an inclined well section wherein at least two
separate flow paths are.arranged',.w.hich flow paths are
split by means of baffles, pipes and the like. Fluid
received from a hydrocarbon enriched part in the well
section is directly pumped to the surface, and fluid
received from a water enriched part in the well section
can be injected back into the formation. At least one
pump is operationally controlled by a detector which is
placed in the vicinity of the splitting means.
Summary
It is an object of the present invention to provide a
system for producing oil from an underground formation to
the surface, wherein the oil can be de-watered below the
surface, such that the water concentration of the
produced oil is sufficiently low that no further de-
watering at the surface is needed before the oil can be
transported away from the wellhead.
It is another object of the invention to provide such
a system which can be used under realistic operating
conditions.
It is yet another object of the invention to provide
a system for underground separation of a well fluid,
which system is easy to operate, robust and efficient.
To this end, in accordance with the present invention
is provided a system for producing de-watered oil from an
underground formation to the surface, which system
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comprises
- a production well extending downwardly from the
surface and having an inlet below the surface;
- a reception well penetrating the underground
formation and capable of receiving well fluid therefrom,
wherein the downstream part of the reception well
comprises a substantially horizontal or inclined section
for primary oil/water separation of the well fluid;
- a water discharge system having an upstream end that
is capable of receiving during normal operation liquid
from the lower region of the downstream part of the
reception well; and
- a secondary underground oil/water separator,
characterised in that the secondary separator has an
upstream end that is capable of receiving during normal
operation liquid from the upper region of the downstream
part of the reception well, the secondary separator
having an outlet for de-watered oil that is in fluid
communication with the inlet of the production well and
an outlet for a water-enriched component that is in fluid
communication with the water discharge system.
The present invention is based on the insight gained
by Applicant by using a proprietary model, that well
fluid flowing in a substantially horizontal or inclined
well section separates under realistic operating
conditions such that near the downstream end of the
horizontal or inclined section the water concentration
(vol%) in the upper, oil-rich component is significantly
larger than the oil concentration (vol%) in the lower,
water-rich component. In particular it has been found,
that the oil-rich component under realistic operating
conditions contains more than 10 vol% of water. The
water-rich component can have an oil concentration
between 0.01 vol% and 0.1 vol%. In the specification and
in the claims the expressions 'upper region' and 'lower
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region' are used in connection with the horizontal section
to refer to the space above a horizontal plane intersecting
the horizontal section, and the expressions also refer to a
space of the same form when used in relation to an inclined
section. The expression "substantially horizontal" section
is used in order to account for the fact that directional
underground drilling in practice may result in deviations
from an intended horizontal direction. An inclined section
is a well section that is not substantially horizontal, and
can have an inclination angle of up to 80 degrees from a
horizontal plane, wherein the well section is upwardly
inclined from its upstream part where well fluid is
received.
According to one broad aspect, the invention
provides system for producing de-watered oil from an
underground formation to the surface, said system
comprising: a production well extending downwardly from the
surface and having an inlet below the surface; a reception
well penetrating the underground formation and capable of
receiving well fluid therefrom, wherein the downstream part
of the reception well comprises a substantially horizontal
or inclined section for primary oil/water separation of the
well fluid; a water discharge system having an upstream end
that is capable of receiving during normal operation a
water-rich liquid from the lower region of the downstream
part of the reception well; and a secondary underground
oil/water separator, characterized in that the secondary
separator has an upstream end that is capable of receiving
during normal operation of an oil-rich liquid from the upper
region of the downstream part of the reception well, the
secondary separator having an outlet for de-watered oil that
is in fluid communication with the inlet of the production
well and an outlet for a water-enriched component that is in
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fluid communication with the water discharge system.
According to another broad aspect, the invention
provides a system for producing de-watered oil from an
underground formation to the surface, said system
comprising: a production well extending downwardly from the
surface and having an inlet below the surface; a reception
well penetrating the underground formation and capable of
receiving well fluid therefrom, wherein the reception well
comprises a primary oil/water separation means, the
reception well connected to the production well; and a
secondary underground oil/water separation means wherein the
secondary underground oil/water separation means is
effective to remove water from an oil-rich phase produced by
the primary oil/water separation means.
Brief Description of the Drawings
The present invention will now be described by way
of example in more detail with reference to the accompanying
drawings, wherein
Figure 1 shows a first result of model
calculations of the separation of a well fluid in a
horizontal pipe,
Figure 2 shows a second result of model
calculations of the separation of a well fluid in a
horizontal pipe,
Figure 3 shows schematically a first embodiment of
the present invention,
Figure 4 shows schematically a second embodiment
of the present invention,
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Figure 5 shows schematically a third embodiment of
the present invention,
Figure 6 shows schematically a fourth embodiment
of the present invention,
Figure 7 shows schematically an embodiment of a
static separator suitable for use as secondary separator in
the present invention, and
Figure 8 shows schematically a detail of the
embodiment of the static separator shown in Figure 7.
Detailed Description
Reference is now made to Figure 1, in which are
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displayed results of calculations that have been
performed using the model developed by Applicant.
Figure 1 shows, for an oil/water mixture flowing in a
horizontal pipe, the calculated water concentration
(vol%) of the oil-rich component in the upper region at
the end of the horizontal pipe (ordinate) as a function
of the length of the horizontal pipe in meters
(abscissa).
The calculations were performed by applying the
proprietary model, which model allows to estimate
parameters that characterize the separation of a flowing
oil/water mixture in horizontal pipes into an upper, oil-
rich component and a lower, water-rich component. The
model takes into account a number of input parameters,
including viscosities and flow rates of oil and water,
pipe diameter, initial droplet size. The model has been
experimentally verified under field conditions in
horizontal pipes.
For the calculations input parameters have been
selected such that they are typical and fall within the
range of realistic operating conditions for the
application of the present invention. The selected input
parameters include oil density 790 kg/m3, viscosity of
the oil 1 mPa.s, flow rate 2000 m3/day, diameter of the
pipe 0.23 m, overall water concentration of the mixture
50 vol%, initial water droplet size 50 m.
As will be clear from Figure 1, the concentration of
water in the oil-rich component decreases with increasing
length of the horizontal pipe. The model predicts, that
at a length of 1000 m the oil-rich component contains ca.
12 vol% water.
For other results of the model calculations reference
is made to Figure 2. Figure 2 shows, for an oil/water
mixture flowing in a horizontal pipe, the calculated
water concentration (vol%) of the oil-rich component in
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the upper region at the end of a horizontal pipe having a
length of 1000 m (ordinate), as a function of the
viscosity of the oil in mPa.s (abscissa), for flow rates
of 1000 m3/day (curve 1), 1600 m3/day (curve 2) and
2000 m3/day (curve 3). The other input parameters were
the same as used for the calculation of Figure 1.
Reference is now made to Figure 3. The system 1 for
producing de-watered oil from an underground formation 2
comprises a production well 3 extending downwardly from
the surface 4 and having an inlet 5 below the surface 4
and an outlet 6 provided with a wellhead 6a at the
surface 4.
The system further comprises a reception well 7,
penetrating the underground formation 2, and capable of
receiving well fluid therefrom through inlet means 8,
wherein the downstream part 9 of the reception well 7
comprises a substantially horizontal section 10, wherein
during normal operation primary separation of well fluid
takes place. The reception well 7 is arranged to connect
at junction 11 to the production well 3 upstream of the
inlet 5.
Furthermore, a water discharge system 12 is provided,
having an upstream end 13 that is arranged to receive
during normal operation liquid from the lower region 14
of the downstream part 9 of the reception well 7.
Optionally, weirs, apertures, splitters, packers or
the like (not shown) may be arranged in or near the
upstream end 13 and/or the junction 11, to guide and keep
separated the streams of fluid components.
The water discharge system 12 in this example is
arranged in a downward extension of the production well 3
below the junction 11, wherein the cross section of the
extension can differ from that of the production well 3.
Further, the water discharge system 12 has a port 15
for receiving a water-enriched component, and a pump 16,
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which is arranged to discharge liquid from the water
discharge system into a well section 17 downstream of the
pump 16. The well section 17 is suitably arranged to
allow injection of the liquid from the water discharge
system into an underground formation (not shown), and the
well section 17 is further provided with means to prevent
water from flowing back.
In addition there is provided a secondary underground
oil/water separator 18 having at its upstream end an
inlet 19 that is capable of receiving during normal
operation liquid from the upper region 20 of the
downstream part 9 of the reception well 7. The
separator 18 has an outlet 21 for de-watered oil that is
in fluid communication with the inlet 5 of the production
well 3, and an outlet 22 for a water-enriched component
that is connected via conduit 23 with the port 15 in the
water discharge system 12. The separator in this example
is arranged in a section of the production well 3, which
section is arranged above the junction 11 in such a way
that the separator can not be bypassed during normal
operation. The section of the production well 3 in which
the separator 18 is arranged can be underreamed.
During normal operation of a system 1 according to
the embodiment shown in Figure 3, the well fluid received
through the inlet means 8 of the reception well 7 flows
to the downstream part 9 including the horizontal
section 10, and separates. Liquid layers are formed in
the upper and lower regions of the downstream part 9 of
the reception wellbore 7, and an interface is formed
between the layers (not shown). Near the downstream end
of the reception wellbore 7 the liquid flowing in the
lower region 14 is a water-rich component, and the liquid
flowing in the upper region 20 is an oil-rich component
of the well fluid. The flow of the well fluid is
separated in this primary separation step to the extent,
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that the water-rich component has sufficiently low oil
concentration.
The water-rich component enters the water discharge
system 12 at the upstream end 13 near the junction 11.
The oil-rich component enters the secondary separator
18 through the inlet 19, and is separated into de-watered
oil, containing typically less than 10 vol% of water,
preferably less than 2 vol%, more preferably less than
0.5 vol% of water, and a water-enriched component, that
can contain between 0.01 vol% and 0.1 vol% of oil. The
separation efficiency depends in part on the type of
separator that is used.
The de-watered oil leaves the separator 18 via the
outlet 21 and flows on through inlet 5 into the
production well 3 and further to the surface 4, where it
is discharged from the system 1 through the wellhead 6a
at the outlet 6. The water-enriched component leaves the
separator via the outlet 22 and conduit 23 and mixes at
port 15 with the water-rich component to form de-oiled
water in the water discharge system 12. During normal
operation, the water discharge system 12 will be filled
up to a certain water level (not shown) with de-oiled
water. The de-oiled water is discharged via well
section 17 by means of pump 16.
As becomes clear from the foregoing description of
the system depicted in Figure 3, a particular advantage
of the present invention is, that the well fluid is
separated into de-watered oil and de-oiled water. In the
event, that the de-oiled water is discharged into an
underground formation, the system according to the
present invention produces only de-watered oil to the
surface.
The curvature of the well section between the
substantially horizontal section 10 and the junction 11
is designed such that the quality of separation does not
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substantially deteriorate.
Reference is now made to Figure 4, which
schematically shows another embodiment of the present
invention. Parts that are similar to parts discussed with
reference to Figure 3 are referred to with the same
reference numerals. The system 100 is an extension of the
system 1 shown in Figure 3 in that it further comprises a
connection well 101. The connection well 101 in this
embodiment is arranged such that it connects to the
reception well 7 at a junction 102 near the downstream
end 103 of the substantially horizontal section 10, and
to the water discharge system 12 at a junction 106 below
the junction 11. The inlet of the connection well 101 is
arranged at junction 102 so as to receive fluid from the
lower region 14, and the outlet of the connection well
101 at junction 106 is in fluid communication with the
water discharge system.
USA patent publication No. 4,390,067 discloses a well
system comprising at least two wellbores extending
downward from the surface, and connected by at least one
generally horizontal wellbore.
During normal operation of the system 100, the water-
rich component does not enter the water discharge system
from the junction 11. To this end, optionally a
packer 108 can be arranged just below the junction 11,
which packer suitably has an opening for a conduit 23
connecting the outlet 22 to the port 15.
Reference is now made to Figure 5, which shows
schematically a third embodiment of the present
invention. Parts that are similar to parts discussed with
reference to Figure 3 are referred to with the same
reference numerals. The system 200 shown in Figure 5
differs from the system 1 shown in Figure 3, in that the
water discharge system 202 comprises a water discharge
well 204 that is arranged as a branch of the reception
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well 7. The junction 206 of the wells 7 and 204 is
arranged near the outlet of the substantially horizontal
section 10 of the downstream part 9 of the reception
well 7.
During normal operation, well fluid undergoes primary
separation in the substantially horizontal section 10 and
enters, when passing the junction 206 near the downstream
end of the horizontal section, a section 208 having a
lower region 209. The lower region 209 receives the
water-rich component from the lower region 14 of the
downstream part 9 of the reception well 7.
During normal operation, the oil-rich component of
the well fluid flows in a layer in the upper region 210
of the section 208 and then through an upwardly curved
well section 212. From the well section 212 it enters the
secondary oil-water separator 18 through the inlet 19. In
the oil-water separator 18 the oil-rich component is
separated into de-watered oil, and a water-enriched
component. The de-watered oil leaves the separator 18 via
the outlet 21 to inlet 5 of the production well 3, and
further to the surface 4, where it is discharged from the
system 200 through the wellhead 6a at the outlet 6. The
water-enriched component leaves the separator via the
outlet 22 and flows through conduit 23 to port 15 that is
arranged in the lower region 209 of the section 208.
There, the water-enriched component mixes with the water-
rich component to form de-oiled water.
Via conduit 216 having an inlet 217 arranged in the
lower region 209, the de-oiled water is received by the
water discharge system 202. By means of pump 16 the de-
oiled water is pumped through the water discharae
well 204, and disposed through outlet means 218 into the
underground formation 220.
Reference is now made to Figure 6, which shows
schematically a fourth embodiment of the present
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invention. Parts that are similar to parts discussed with
reference to Figure 3 are referred to with the same
reference numerals. The system 300 shown in Figure 6
differs from the system that has been discussed with
reference to Figure 3 in the arrangement of the secondary
oil-water separator and of the water discharge system.
The secondary oil-water separator 18 of the system
300 is arranged in an underreamed section at the lower
end of the production well 3. The separator 18 is
arranged to receive, through its inlet 19, liquid from
the upper region 302 of the horizontal section 10 of the
downstream part 9 of the reception well'7, wherein the
separator 18 is located near the downstream end 303 of
the horizontal section 10. The oil-water separator 18
further has an outlet 21 for de-watered oil that is in
fluid communication with the inlet 5 of the production
well 3, and an outlet 22 for a water-enriched component.
Outlet 22 is connected via conduit 23 to port 15, which
port 15 is arranged in the lower region 304 of the
horizontal section 10, near the downstream end 303 of the
horizontal section 10.
The water discharge system 305 in this embodiment
comprises a water-discharge well 306 of which the slope
declines in the direction of fluid flow. The water-
discharge well 306 has an inlet 310 at its upper end that
connects to the downstream end 303 of the horizontal
section 10. The slope of the water-discharge well 306 is
selected such that an incoming stratified flow is not
substantially disturbed.
Downstream in the water-discharge well 306, at a
position below the lowest level of the horizontal
section 10, a pump 16 is arranged to discharge the de-
oiled water through outlet 312 into the underground
formation 315, and there is further provided means to
prevent water from flowing back (not shown).
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During normal operation of a system 300 as shown in
Figure 6, the well fluid received through the inlet means
8 of the reception well 7 flows to the downstream part 9
including the horizontal section 10, which acts as
primary separator for the well fluid. Liquid layers are
formed in the upper and lower regions of the horizontal
section 10, and an interface is formed between the layers
(not shown). Near the downstream end 303 of the
horizontal section 10 the liquid flowing in the lower
region 304 is a water-rich component, and the liquid
flowing in the upper region 302 is an oil-rich component
of the well fluid. The flow of the well fluid is
separated to the extent, that the water-rich component
has sufficiently low oil concentration.
The oil-rich component enters the secondary separator
18 through the inlet 19, and is separated into de-watered
oil and a water-enriched component, wherein the de-
watered oil is passed to the surface 4 as described with
reference to Figure 3. The water-enriched component
leaves the separator through the outlet 22 and conduit 23
and mixes near port 15 in the lower region 304 with the
water-rich component to form, downstream of port 15, de-
oiled water.
The de-oiled water is received by the water-discharge
well 306 through inlet 310. Below the lowest level of the
substantially horizontals section the water-discharge
well will, during normal operation, be filled with de-
oiled water. By means of pump 16 the de-oiled water is
pumped through the water-discharge well 306, and disposed
through outlet means 312 into the underground
formation 315.
It may be desirable to produce oil from multiple
reception wells by using a single production well and a
single oil/water separator. In this case, the system
according to the invention comprises one or more
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additional reception wells, which penetrate the
underground formation at different locations and receive
well fluid therefrom, wherein the downstream parts of the
additional reception wells are in fluid communication
with the downstream part of the reception well. The
separation of well fluid into water-rich and oil-rich
components may occur in the multiple reception wells
individually, or in a common downstream part after mixing
all well fluid, or partly in both ways.
In the International Patent application with
publication No. WO 98/25005 is disclosed an underground
well system comprising a substantially vertical welibore
and one or more horizontal well sections extending from
the vertical wellbore.
In the International Patent application with
publication No. WO 98/50679 is disclosed an underground
well system comprising a main well and one or more
additional wells, wherein each well extends downwardly
from the surface and comprises a substantially horizontal
section arranged in a production formation. The
horizontal sections of the additional wells are in fluid
communication with the horizontal section of the main
well through the production formation, but do not
physically intersect with the main well.
The underground oil/water separator for use in a
system according to the present invention can be of
various types known in the art, such as for example a
cyclone, a coalescer, or a static separator. With
advantage the separator is a static one, which is
arranged in a separation chamber, wherein the height of
the separation chamber is larger than the thickness of
the oil/water dispersion band that is formed therein
under normal operation conditions. The separation chamber
can with advantage be arranged in an underreamed section
of the production well.
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It has been recognised that in an underground
separation chamber one can take advantage of the physical
conditions in the well, e.g. elevated temperature and
pressure, which influence the separation behaviour of oil
and water such that efficient separation of the liquid
received from the upper region of the downstream part of
the reception well into relatively dry oil and relatively
pure water can be achieved under practically and
economically feasible conditions.
The liquid received during normal operation by a
static separator from the upper region of the downstream
part of the reception well is an oil-rich component of
the well fluid in the form of an oil/water dispersion,
containing more than 10 vol% of water. The separation of
such an oil/water dispersion in a separation chamber
under the influence of gravity can be described by means
of a model developed by Applicant. This so-called
Dispersion Band Model, is published in H.G. Polderman et
al., SPE paper No. 38816, 1997. The model can be used to
describe separation in a separation chamber. An important
mechanism of separation is based on coalescence of small
water droplets in the dispersion band, which sink to the
lower layer once the drops have grown large enough.
During normal operation, three liquid layers are formed:
a bottom layer of relatively pure water, a middle layer
containing an oil and water dispersion and an upper layer
of relatively dry oil. The middle layer is also referred
to as the dispersion band.
Suitably, the inlet and the outlets of the separator
are arranged such that the feed and the separated
components flow vertically or nearly vertical in and out
of the separation chamber.
In a first embodiment of such a static separator the
separator further comprises a flow distributor means,
arranged to distribute at a predetermined vertical
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position the liquid over the cross-sectional area of the
separation chamber. Preferably, the liquid is admitted
into the separation chamber at a predetermined vertical
position through one or more openings at a local flow
velocity below 1 m/s. In the separation chamber the
liquid is allowed to separate into a lower layer of a
water-enriched component, a middle layer of an oil and
water dispersion component and an upper layer of an de-
watered oil component. Liquid from the upper and lower
layers can be withdrawn via the outlets for de-watered
oil and the water-enriched component, respectivel.y. The
separator can further comprise a level detector means for
measuring the vertical position of the interface between
two liquid layers and a flow control means in order to
maintain during normal operation an interface between two
liquid layers at a predetermined vertical level.
In a second embodiment, a static separator for use as
secondary separator with the present invention further
comprises
- a stack of vertically spaced apart inclined plates,
wherein between each pair of neighbouring plates a
separation space is defined;
- a substantially vertical inlet conduit communicating
with the separator's upstream end, which inlet conduit
traverses the stack of plates and is arranged to receive
the liquid from the upper region of the downstream part
of the reception well at its lower end, and is provided
with one or more fluid outlets each of which opens into a
separation space;
- a substantially vertical oil collection channel having
an oil outlet at its upper end communicating with the
separator's outlet for the de-watered oil, which oil
collection channel has one or more oil inlets, each oil
inlet being arranged to receive fluid from the uppermost
region of a separation space, wherein at least the plate
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immediately below each oil inlet is provided with a
vertically upward pointing baffle; and
- a substantially vertical water collection channel
having a water outlet at its lower end communicating with
the separator's outlet for the water-enriched component,
which oil collection channel has one or more water
inlets, each water inlet being arranged to receive fluid
from the lowermost region of a separation space, wherein
at least the plate immediately above each water inlet is
provided with a vertically downward pointing baffle.
Reference is now made to Figures 7 and 8. Figure 7
shows an example of a static separator 410 which is
arranged in a separation chamber 406 in an underreamed
section of the production well (not shown). The
separation chamber 406 has a substantially circular cross
section. The vertical wall 408 of the separation
chamber 406 is formed by the surrounding formation 409,
but it will be understood that the wall can also be
provided by a well tubular, such as a casing. The wall of
the separation chamber also forms the wall of the
separator. The static separator 410 comprises a stack of
inclined, substantially flat plates 430, 431, 432 that
are arranged substantially parallel to each other and
vertically spaced apart at an equal distance. The space
delimited between two neighbouring plates is referred to
as the separation space. For example, plates 430 and 431
define the separation space 435, plates 431 and 432
define the separation space 436. Underneath the lowest
plate 432 of the stack of plates a parallel base
plate 437 is arranged, wherein the outer rim of the base
plate sealingly engages the walls of the separation
chamber 406. Between the plate 432 and the base plate 437
a further separation space 438 is defined.
The stack of plates is traversed by the inlet
conduit 440, which extends vertically upwardly from an
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opening 442 through the stack of plates in the centre of
the separation chamber 406. The passage of the inlet
conduit through a plate, for example the passage 443
through plate 431, is thereby arranged such that the wall
of the inlet conduit 440 sealingly fits to the plate, for
example plate 431, thereby preventing fluid communication
between neighbouring separation spaces, for example
separation spaces 435 and 436, along the inlet conduit.
Further, the inlet conduit is provided with radial outlet
openings 444, 445, 446, which open into the separation
spaces 435, 436, 438, respectively. It will be clear,
that further outlet openings can be arranged opening into
different radial directions. An outlet opening is with
advantage arranged in the direction of the axis in the
horizontal plane around which the plates are inclined,
i.e. in Figure 7 an axis perpendicular to the paper
plane.
Further details about the inclined plates will now be
discussed with reference to Figure 8, wherein
schematically the plates 431 and 432 of Figure 7 are
shown. The rim 447 of plate 431 includes at the upper
side 448 of the plate 431 a straight edge 449 to which an
upward pointing baffle plate 450 is attached. At the
lower side 452 the rim 447 includes a straight edge 454
to which a downward pointing baffle plate 456 is
attached.
Referring again to Figure 7, the other inclined
plates of the stack of plates are similarly provided with
upward and downward pointing baffles 458, 459, 460, 461
at the their upper and lower sides, respectively. The
remaining parts of the rim of each inclined plate to
which no baffle is attached are arranged to sealingly
engage the wall 408.
The static separator 410 further comprises an oil
collection channel 465, which is formed by the space
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segment delimited by the upward pointing baffles, 458,
450, 459, and the wall 408. The oil collection
channel 465 comprises oil inlets, for example oil
inlet 470 arranged to receive fluid from the uppermost
region 472 of the separation space 436. Oil inlet 470 is
defined by the upper edge 449 of the plate 431 and the
upward pointing baffle 459 of the plate 432 immediately
below the oil inlet 470. The oil collection channel 465
further comprises an outlet 473 in communication with the
outlet 415 of the static separator 410.
Opposite to the oil collection channel 465 the
separator 410 comprises a water collection channel 475,
which is formed by the space segment delimited by the
downward pointing baffles, 460, 456, 461, and the
wall 408. The water collection channel 475 comprises
water inlets, for example water inlet 480 arranged to
receive fluid from the lowermost region 482 of the
separation space 435. Water inlet 480 is defined by the
lower edge 454 of the plate 431 and the downward pointing
baffle of the plate 430 immediately above the water
inlet 480. The water collection channel 465 further
comprises an outlet 483 in communication with the
outlet 418 of the separator 410.
The plates 430, 431 and 432 with the attached baffles
are arranged such that the shortest horizontal distance
between an upward pointing baffle and the wall 408
increases from bottom to top, and that the shortest
horizontal distance between a downward pointing baffle
and the wall 408 increases from top to bottom. In this
way the cross-sectional areas of both the oil collection
channel 465 and the water collection channel 475 increase
in the direction towards their respective outlets 473 and
483. Since the separator 410 does not contain parts that
are moving during normal operation it represents a static
oil-water separator.
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During normal operation fluid enters the static
separator 410 its upstream end 412, enters the inlet
conduit 440 at the opening 442 and is admitted into the
interior of the separation spaces 435, 436, 437 via the
outlet openings 444, 445 and 446. It has been found that
good separation results are obtained if all openings have
the same cross-sectional area. Good results are obtained
if the diameter of the openings is of the order of the
diameter of the inlet conduit, such that the pressure
drop over the opening is small.
The separation will now be discussed. To this end we
take a closer look on the separation space 436 between
plates 431 and 432. In this separation space 436, three
liquid layers are formed, an upper, de-watered oil layer,
a middle dispersion band layer and a lower, water-
enriched layer. The de-watered oil layer flows towards
the uppermost region 472 of the separation space 436,
from where it leaves the separation space to enter the
oil collection channel through inlet 470. The water-
enriched layer flows towards the lowermost region 485 of
the separation space 436, from where it enters the water
collection channel through inlet 486. Separation in the
spaces 435 and 435 is similar. The oil collection
channel 465 receives a de-watered oil component from all
separation spaces, and since the cross-section of the
channel widens towards the outlet 473, the vertically
upward flow velocity of the de-watered oil component in
the channel 465 can remain substantially constant. From
the outlet 473 the collected de-watered oil component
flows to the separator's outlet for de-watered oil 415.
The water-collection channel 475 receives a water-
enriched component from all separation spaces, and since
its cross-section widens from top to bottom towards the
outlet 483, the vertically downward flow velocity of the
water-enriched component in the channel 475 can remain
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substantially constant. From the outlet 483 the collected
water-enriched component flows to the separator's outlet
for a water-enriched component 418.
In a further embodiment the inclined plates can have
substantially the form of funnels arranged substantially
parallel to each other, wherein each funnel is provided
with a central opening.
By installing a stack of vertically spaced apart
inclined plates the efficiency of a separation chamber
can be increased, i.e. a chamber of smaller height can
handle the same specific throughput as a larger
separation chamber without a plate pack. In practice
often a reduction of the required height of the
separation chamber by a factor in the range of from 1.5
to 6 can be achieved. Sometimes, the height of the
separation chamber is not a limiting factor for the well
design, and in this case a separator without a stack of
plates can be used.
Typical dimensions of the separation chamber have
been calculated using the Dispersion Band Model under the
following assumptions: gross flow rate through the
separator 1000 m3/day of well fluid containing 50 vol% of
water, dry oil viscosity 0.001 Pa.s. In this case a
separation chamber of about 1 m diameter and 5 m height
is required. For comparison it is noted that by
installing a stack of plates in the separation chamber
the height requirement can be decreased to for example 2
m. Suitably the height/diameter ratio of the separation
chamber is smaller than 6, wherein under diameter is
understood the diameter of a circle having the same
cross-sectional area as the volume of the separation
chamber divided by its height.
It will be appreciated, that in practical
applications of the present invention additional
technical measures may be implemented which are well
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known in the art and of which the expert is master. By
way of example some of those measures will briefly be
described hereinafter.
The wells of a system according to the present
invention, or sections thereof, may be provided with
casing, tubing, packing, flow controllers, measurement
equipment, data communication lines, power transfer lines
to underground equipment or other means known in the art
for operating and controlling a well system.
In the event that the well fluid comprises in
addition to oil and water also gas, it is possible that
in the downstream part of the reception well a gas layer
is formed on top of the layer in which the remainder
liquid flows. Gas may decrease the separating efficiency
of the separator. It may therefore be advantageous to
arrange an outlet for gas connected to a gas-discharge
system for gas at a suitable position in the system.
It may be desirable to perform measurements using
underground equipment. This may be of advantage for
monitoring and controlling the operation of the system.
As an example, measurement equipment may be installed
to monitor the oil, gas or water content of fluids at
certain positions in the system. E.g., the water or oil
content of the de-oiled water, the water-rich component,
the water-enriched component, or of the de-watered oil,
may be measured by suitable equipment.
Further, although the exact vertical level of an
interface between layers of different components at a
certain position in the system is generally not critical
for the function of the system, and may vary within
predetermined limits, it may be desirable to measure the
level by a detector.
The result of such a measurement may e.g. be used to
control the flow rate of a fluid at a certain position in
the system to stay within predetermined limits. It is
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well known in the art how to control a flow rate in a
system according to the present invention, e.g. the flow
rate of inflowing well fluid, liquid from the upper
region or from the lower region of the downstream part of
the reception well, de-oiled water or de-watered oil. To
this end, the system may comprise controllable valves,
pumps, restrictions, movable sleeves, adjustable
apertures or other suitable equipment.
It may be desirable to promote the separation of
fluid components by physical or chemical means, e.g. by
the injection of chemicals that are known in the art.
In the event that an inclined well section is
provided for primary separation of the well fluid, it can
be advantageous to arrange at the downstream end of the
inclined section, in the area upstream of and around the
secondary separator, a substantially horizontal section,
which can be for example up to 100 meters long.
It will be appreciated, that the de-oiled water can
be injected in the underground formation, from which well
fluid is removed. In this way, the injection of de-oiled
water can serve to maintain the pressure in the
underground formation.
Thus, the present invention provides a system for
producing oil from an underground formation to the
surface, wherein the oil can be de-watered below the
surface, such that the water concentration of the
produced oil is sufficiently low that no further de-
watering at the surface is needed before the oil can be
transported away from the wellhead.
