U.S. patent number RE39,292 [Application Number 10/879,890] was granted by the patent office on 2006-09-19 for apparatus and method for downhole fluid phase separation.
This patent grant is currently assigned to BJ Services Company. Invention is credited to Gordon D. Latos, John E. Ravensbergen.
United States Patent |
RE39,292 |
Latos , et al. |
September 19, 2006 |
Apparatus and method for downhole fluid phase separation
Abstract
Method and apparatus for separating fluids flowing through a
downhole well passageway including separating fluids pumped
downhole, centrifugal separation, gradually increasing centrifugal
acceleration, the establishment of annular flow, gradually
establishing annular flow, a receiving chamber of increasing
cross-sectional area of flow and method and apparatus for use of a
fluid separator tool with tubing for downhole well operations, in
particular with coiled tubing.
Inventors: |
Latos; Gordon D. (Calgary,
CA), Ravensbergen; John E. (De Winton,
CA) |
Assignee: |
BJ Services Company (Houston,
TX)
|
Family
ID: |
21846341 |
Appl.
No.: |
10/879,890 |
Filed: |
June 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09028939 |
Feb 24, 1998 |
06138757 |
Oct 31, 2000 |
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Current U.S.
Class: |
166/265;
166/105.5 |
Current CPC
Class: |
E21B
21/14 (20130101); E21B 21/002 (20130101) |
Current International
Class: |
E21B
43/38 (20060101) |
Field of
Search: |
;166/72,90.1,105.5,265,266 ;210/170,747 ;55/421 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Walker; Zakiya
Attorney, Agent or Firm: Howrey LLP
Claims
What is claimed is:
1. A downhole method for separating fluids flowing through a well
comprising: pumping a fluid mixture downhole; centrifugally
accelerating downward flow of pumped fluid through at least a
portion of a downhole passageway; .[.and.]. separating
centrifugally accelerated fluid by density into .[.at least two
fluid streams.]. .Iadd.a lower density and a higher density fluid
stream, the higher density fluid stream continuing through a
downhole tool.Iaddend..
2. A downhole method for separating fluids flowing through a well,
comprising: accelerating, at an increasing rate, centrifugally the
flow of fluid through at least a portion of a downhole passageway
using a plurality of vanes having pitch angles graduating from low
to high in a direction of flow over a substantial portion of a vane
length while maintaining cross-sectional area of flow substantially
constant; and separating centrifugally accelerated fluid by density
into at least two fluid streams.
3. A downhole method for separating fluids flowing through a well,
comprising: establishing through gradual increase, in at least a
portion of a downhole passageway defined by a housing bore, annular
fluid flow having cross-sectional area of flow with an average
radius that gradually increases in value over a length of a portion
of the passageway from a value below 75% of a radius of the
corresponding passageway portion to a value above 75% of the radius
of the corresponding passageway portion; centrifugally accelerating
flow of fluid through at least a portion of the downhole
passageway; and separating centrifugally accelerated fluid by
density into at least two fluid streams.
4. The method of claims 1 or 2 that includes establishing, in at
least a portion of the downhole passageway, annular fluid flow.
5. The method of claims 1, 2 or 3 that includes gradually
establishing, in at least a portion of the downhole passageway,
annular fluid flow.
6. The method of claims 1 or 2 that includes gradually
establishing, in at least a portion of the downhole passageway
defined by a housing bore, annular fluid flow having a
cross-sectional area of flow with an average radius greater than
75% of a radius of the corresponding passageway portion.
7. The method of claims 1 or 3 that includes accelerating, at an
increasing rate, centrifugally the flow of fluid through at least
the portion of the downhole passageway.
8. The method of claims 1, 2 or 3 that includes receiving
centrifugally flowing fluid in a chamber defining a flow path with
a cross-sectional area of flow that gradually increases.
9. The method of claims 2 or 3 that includes pumping a fluid
mixture downhole and wherein the centrifugally accelerated flow is
established with at least a portion of the downward pumped
fluid.
10. The method of claims .[.1,.]. 2 or 3 wherein the at least two
separated fluid streams include a predominately liquid stream and a
predominately gas stream.
11. The method of claim 10 wherein the predominately liquid stream
contains less than 10% gas by volume.
12. The method of claim 3 wherein the centrifugal accelerating
occurs subsequent to the establishing of annular flow.
13. The method of claims .[.1,.]. 2 or 3 wherein a pressure loss
from applying the method for at least one separated fluid stream is
less than 15%.
14. Surface and downhole apparatus for separating fluids flowing in
a well, comprising: a pump attached at the surface to tubing
attached to a downhole assembly wherein at least a portion of the
downhole assembly defines a fluid passageway having a direction of
flow away from the pump; at least one vane attached within a
portion of the fluid passageway, the vane passageway portion being
in fluid communication with the pump, and means, in fluid
communication with the vane passageway portion, for separating
centrifugally accelerated fluid by density into .[.at least two
streams.]. .Iadd.a lower density and a higher density fluid stream,
wherein the heavier fluid stream is utilized in a downhole
tool.Iaddend..
15. Apparatus for separating fluids flowing in a well, comprising:
a downhole assembly having a portion defining a fluid passageway
with the fluid having a direction of flow in the passageway having
a substantially constant cross-sectional area of flow; a plurality
of vanes attached within the portion of the fluid passageway, the
vanes having pitch angles graduating from low to high in the
direction of flow over a substantial portion of the vane length;
and means, in fluid communication with the vane passageway portion,
for separating centrifugally accelerated fluid by density into at
least two streams.
16. Apparatus for separating fluid flowing in a well, comprising:
at least a portion of a downhole assembly defining an annular fluid
passageway within a housing bore, the annular passageway defining a
fluid flow path having a cross-sectional area of flow with an
average radius gradually increasing from below to greater than 75%
of a radius of the corresponding passageway portion; a vane
attached within a portion of a passageway defined by the portion of
the downhole assembly; and means, in fluid communication with the
vane passageway portion, for separating centrifugally accelerated
fluid by density into at least two streams.
17. The apparatus of claim 16 wherein the vane is attached within a
portion of the annular passageway.
18. The apparatus of claims 14, 15 or 16 wherein at least a portion
of the downhole assembly defines an annular passageway having a
gradually increasing annularity and a gradually increasing inside
radius in a direction of fluid flow.
19. The apparatus of claims 14 or 15 wherein at least a portion of
the downhole assembly defines an annular fluid passageway within a
housing bore, the annular passageway defining a flow of fluid
having a cross-sectional area of flow with an average radius
greater than 75% of a radius of the corresponding passageway
portion.
20. The apparatus of claims 14 or 16 wherein the vane passageway
portion defines a direction of flow and the vane has a pitch angle
graduating from low to high in the direction of flow.
21. The apparatus of claim 14, 15 or 16 that includes a chamber, in
direct fluid communication with the vane passageway portion, the
chamber defining a flow of fluid with a cross-sectional area of
flow that gradually increases in a direction of flow.
22. The apparatus of claim 15 or 16 that includes a pump attached
at a surface to tubing attached to the downhole assembly in the
well and wherein the fluid separated is fluid pumped down.
23. The apparatus of claims 14, 15 or 16 wherein the apparatus is
less than three feet long.
24. Apparatus for separating fluids flowing in a well, comprising:
at least a portion of a downhole assembly defining an annular fluid
passageway, a portion of the annular passageway having gradually
increasing annularity and gradually increasing inside radius in a
direction of fluid flow; a vane attached within a portion of a
passageway defined by a portion of the downhole assembly; and
means, in fluid communication with the vane passageway portion, for
separating centrifugally accelerated fluid by density into at least
two streams; and wherein the portion of the annular passageway of
increasing annularity includes a tapered barrier located in the
passageway.
25. The apparatus of claim 24 wherein the vane passageway portion
is attached to a downstream end of the annular fluid passageway
with gradually increasing annularity.
26. Apparatus for separating fluids flowing in a well, comprising:
at least one vane attached within a portion of a fluid passageway
defined by at least a portion of a downhole assembly; a chamber, in
direct fluid communication with the vane passageway portion, the
chamber defining a flow of fluid with a cross-sectional area of
flow that gradually increases; means, in fluid communication with
the chamber, for separating centrifugally accelerated fluid by
density into at least two streams; and wherein the chamber defining
a flow of fluid with an increasing cross-sectional area of flow
contains a tapered barrier located therein.
27. A method for operating a downhole assembly in a well with
coiled tubing, comprising: pumping a fluid mixture down tubing to a
downhole assembly; separating the fluid mixture downhole by density
into at least two fluid streams; and using at least one fluid
stream with a downhole assembly tool.
28. The method of claim 27 that includes using at least one fluid
stream with a downhole assembly motor.
29. The method of claim 27 that includes using at least one fluid
stream with a downhole assembly jetting tool.
30. The method of claim 27 that includes venting at least one fluid
stream to the wellbore.
31. The method of claim 27 that includes separating the fluid
mixture such that one stream is predominately liquid and one stream
is predominately gas.
32. The method of claim 31 wherein the liquid stream contains less
than 10% of gas.
33. The method of claim 27 wherein a loss of pressure of at least
one separated fluid stream pumped downhole, occasioned by the
separating, is less than 10% of the tool to wellbore pressure
differential.
34. The method of claim 27 wherein a loss of pressure of at least
one separated fluid stream piped downhole, occasioned by the
separating, is less than 100 psi.
35. Surface and downhole apparatus for use at a well, comprising:
tubing attached to a downhole .[.assembly.]. .Iadd.tool.Iaddend.; a
pump attached at the surface to the tubing; and a fluid separator
associated with the downhole .[.assembly.]. .Iadd.tool,
.Iaddend.located and structured in combination with the
.[.assembly.]. .Iadd.tool, .Iaddend.to separate by density a fluid
mixture pumped down the tubing into .[.at least two fluid
streams.]. .Iadd.a lower density and a higher density fluid stream,
wherein the heavier fluid stream is directed through the downhole
tool.Iaddend..
.[.36. The apparatus of claim 35 that includes a tool associated
with the downhole assembly in fluid communication with at least one
separated fluid stream..].
37. The apparatus of claim 3.[.6.]. .Iadd.5, where.Iaddend.in the
.Iadd.downhole .Iaddend.tool comprises a downhole motor.
38. The apparatus of claim 3.[.6.]. .Iadd.5, .Iaddend.wherein the
.Iadd.downhole .Iaddend.tool comprises a downhole jetting tool.
39. The apparatus of claim 35 wherein the fluid separator comprises
a centrifugal separator.
40. The apparatus of claim 35 wherein the tubing is coiled
tubing.
.Iadd.41. The method of claim 1, wherein the downhole tool
comprises a downhole motor..Iaddend.
.Iadd.42. The method of claim 1, wherein the downhole tool
comprises a downhole jetting tool..Iaddend.
.Iadd.43. The apparatus of claim 14, wherein the downhole tool
comprises a downhole motor..Iaddend.
.Iadd.44. The apparatus of claim 14, wherein the downhole tool
comprises a downhole jetting tool..Iaddend.
.Iadd.45. A downhole method for separating fluids flowing through a
well comprising: pumping a fluid mixture downhole; centrifugally
accelerating downward flow of a pumped fluid mixture through at
least a portion of a downhole passageway; separating a
centrifugally accelerated fluid mixture by density into a liquid
and a gas stream; and operating a downhole tool with the liquid
stream..Iaddend.
.Iadd.46. The method of claim 45, wherein the downhole tool
comprises a downhole motor..Iaddend.
.Iadd.47. The method of claim 45, wherein the downhole tool
comprises a downhole jetting tool..Iaddend.
.Iadd.48. Surface and downhole apparatus for separating fluids
flowing in a well, comprising: a pump attached at the surface to
tubing attached to a downhole assembly wherein at least a portion
of the downhole assembly defines a fluid passageway having a
direction of flow away from the pump; at least one vane attached
within a portion of the fluid passageway, the vane passageway
portion being in fluid communication with the pump; and means, in
fluid communication with the vane passageway portion, for
separating a centrifugally accelerated fluid mixture by density
into a liquid and a gas stream, wherein the liquid stream is
directed to a downhole tool..Iaddend.
.Iadd.49. The apparatus of claim 48, wherein the downhole tool
comprises a downhole motor..Iaddend.
.Iadd.50. The apparatus of claim 48, wherein the downhole tool
comprises a downhole jetting tool..Iaddend.
.Iadd.51. Surface and downhole apparatus for use at a well
comprising: tubing attached to a downhole tool; a pump attached at
the surface to the tubing; and a fluid separator associated with
the downhole tool to separate by density a fluid mixture pumped
down the tubing into a liquid and a gas stream, wherein the
downhole tool utilizes the liquid stream..Iaddend.
.Iadd.52. The apparatus of claim 51, wherein the downhole tool
comprises a downhole motor..Iaddend.
.Iadd.53. The apparatus of claim 51, wherein the downhole tool
comprises a downhole jetting tool..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to fluid downhole separators and fluid
separating, and more particularly to downhole fluid separators
using centrifugal separating techniques and wherein a plurality of
fluids pumped downhole are separated and where the separation is
particularly useful in coiled tubing operations.
BACKGROUND OF THE INVENTION
There are occasions in the oil and gas industry when a gas may be
pumped downhole together with a liquid phase such as a treatment
fluid or a drilling fluid. In particular it may be useful to pump
nitrogen gas downhole during drilling or during well workover
operations. There could be a variety of purposes for pumping
downhole a gas with a liquid phase. Such purposes might include
helping to lift liquids back to the surface and/or lowering the
pressure exerted by the combination of fluids against fragile
welllbores. "Underbalanced" drilling, for instance, typically
utilizes a gas added to a drilling fluid to "underbalance" the
pressure between the drilling fluid and portions of the formation
that are open downhole.
One illustration of a well workover application where it might be
useful to pump gas downhole is in rotary jet cleaning. In rotary
jet cleaning a liquid is pumped downhole and out of a rotary jet
cleaning tool. Gas could be advantageously added to the liquid in
so far as the gas could help lift and circulate the cleaning liquid
back up hole, possibly enhancing the liquid's capacity to carry
debris. Drilling with a downhole motor and rotary jet drilling
might have similar applications in which it could be advantageous
to add gas to a working liquid, at least for lifting purposes.
However, running mixed gas/liquid phase through a downhole
hydraulically powered motor or other apparatus, such as a downhole
drilling motor or a rotary jet cleaning tool, is not favored. The
gas/liquid phase neither optimizes downhole motor performance nor
optimizes maintenance of the motor parts. Sending a mixed
gas/liquid phase through a rotary jet cleaner, in addition, may
result in the loss of optimum cleaning power.
One aspect of the instant invention, therefore, is a methodology
and apparatus affording the ability to remove a gas phase at or in
a bottomhole assembly (BHA) when the presence of the gas downhole
could be helpful but when it would also be useful to prevent the
gas from invading and damaging elastomers in a drilling motor
and/or to optimize the cleaning performance of a rotary jet cleaner
by excluding a gas phase.
Existing commercially available downhole liquid/gas flow separators
seem to be designed for separating production fluids. These are
fluids flowing up either under natural pressure or being pumped.
These separators appear optimized for narrow ranges of gas volume
fraction and/or for high values of entry or initial gas volume
fraction. They appear typically optimized for entry gas volume
fractions of between 90% and 100% and for exit gas volume fractions
of between 15% and 50%. See U.S. Pat. No. 5,482,117, column 1, line
58. These entry ranges are too high and too narrow to be useful for
generally separating fluid mixtures, in particular gas/liquid mixed
phase fluids, that might be pumped downhole in either a drilling
application or in a jetting application or in other workover
applications. The exit volume fractions are also too high.
The problems involved in cost effectively, efficiently and
sufficiently separating pumped fluids flowing downhole are
different from the problems involved in sufficiently separating
well fluids produced into a well to be flowed or pumped up.
A further aspect of the present invention includes the design of an
efficient and effective downhole fluid phase separator, which
includes gas/liquid separating, that can effectively and
efficiently operate without excessive loss of pressure to the fluid
pumped downhole and can operate over a range of supplied gas volume
fractions that might run from 10% through 90%. Further, the
separator must not be too long. Important aspects of the invention
include the length of the separator, ideally below three (3) feet,
and the pressure drop caused by the tool, preferably below 10% of
the supplied fluid pressure. The outside diameter of the tool will
be limited by the diameter of the wellbores through which the
bottomhole assembly is designed to run. Simplicity of operation and
the absence of moving parts are further advantageous features found
in embodiments of the instant design which enhance the value of the
tool.
Disclosed herein is a preferred embodiment for a fluid
(particularly including liquid/gas) phase separator for use on
fluid mixtures pumped downhole, and its methods of use. One prime
application lies with coiled-tubing-based downhole operations. The
device separates fluids by density, including nitrified treatment
fluids and nitrified drilling fluids. The fluids are separated into
at least two constituent phases or portions. The device can be
structured and designed to optimize the separation of one stream,
such as a liquid stream, so that the stream is relatively free of a
second fluid, such as a gas. "Relatively" in the instant
environment means at least 75% free. Preferred embodiments have
achieved significantly greater percentages of separation.
For purposes herein fluids are distinguished or characterized as
separate fluids by their density, or at least by their capacity to
be separated by density. Use of the term fluid mixture implies a
mixture of fluids with different densities or at least a mixture of
fluids that can be separated into at least two streams by density.
The disclosed tool and method separate a fluid mixture into at
least two fluid streams by density and subsequently permit
directing each stream to a different path in accordance with useful
applications.
In the present invention separating fluids by density is preferably
achieved by inducing centrifugal acceleration, or a swirling flow
path, to a moving fluid stream. Preferably a significant annular
flow is first or also induced within the limits of space available.
Preferably also a gradually expanding flow path in terms of
cross-sectional area of flow is defined in a chamber that receives
centrifugally accelerated fluids.
It should be understood that the distinct stages of the disclosed
preferred embodiment herein could be overlapped in alternate
designs. Distinct steps disclosed by the preferred embodiment could
be made simultaneous or partially simultaneous. The instant design
facilitated testing of functionality. With the present design the
length of the tool has been shown to be able to be satisfactorily
minimized, as has the loss of head pressure for the pumped fluids
due to the separation process. High efficiencies in the separation
of gas from liquid have been shown to be achievable.
In regard to gas/liquid separation, which is a prime application,
shop tests have indicated that a separation efficiency can be
achieved such that less than three percent (3%) of the original gas
is left in a liquid fluid stream. This was achieved with a tool
having less than three feet of length (More than 3% of the original
liquid may or may not be left in the gas, as this may not be a
critical parameter.) It will be understood that multiple stages
could be utilized to improve further gas separation efficiency.
Alternately, gas separation efficiency could be improved by
accepting more liquid in the gas discharge stream.
The combination of features designed into preferred embodiments of
the tool, and designed into preferred embodiments of the
methodology disclosed, advantageously provides the ability to
function effectively, efficiently and economically under
significant size and performance limitations, as required for
downhole operations.
SUMMARY OF THE INVENTION
The invention teaches a downhole method and apparatus for
separating fluids flowing through a passageway in a well. The
method includes centrifugally accelerating flow of fluid downhole
through at least a portion of a downhole passageway and separating
centrifugally accelerated fluid by density into at least two fluid
streams. In one aspect the novel method includes pumping a fluid
mixture downhole and centrifugally accelerating and separating at
least a part of the fluid pumped downward. Fluid pumped "downward"
is intended to cover fluid flowing in the wellbore in the direction
from the well head or surface and toward the well toe or bottom. It
is conceivable that fluid in this "downward" flow path (which is to
be distinguished from flow of fluid in the well "upward" or toward
the surface) could literally be flowing, gravitationally speaking,
"up" for a period of time (or at least not gravitationally "down",
as in a horizontal wellbore.) In a second aspect the novel method
includes receiving centrifugally accelerated fluid in a chamber
defining a flow path having a cross-sectional area of flow that
gradually increases. (As illustrated, this can be accomplished
without increasing the outside diameter of the flow passageway.) In
a third aspect the novel method includes centrifugally accelerating
flow of fluid through at least a portion of a downhole passageway
wherein the centrifugal acceleration occurs at an increasing rate.
A fourth aspect of the invention involves establishing in at least
a portion of a downhole well passageway annular fluid flow with the
annular flow path having a cross-sectional area of flow with an
average radius greater than 75% of the passageway radius.
(Passageway radius refers to one-half of the ID of the housing
defining the passageway). The average radius of fluid flowing
through a passageway with an open (unobstructed) cross-sectional
area of flow, for example (as the term average is used herein)
would be 50% of the passageway radius. When the term "average"
radius is used, the average of all of the distances out from center
of the passageway at which fluid flows is meant. No account is
intended to be taken, in speaking of an "average" radius, of the
fact that a greater volume of fluid flows at a greater radius. A
fifth aspect of the invention includes gradually establishing
annular fluid flow, preferably prior to or during centrifugal
acceleration, in at least a portion of a downhole passageway.
Various combinations of the above embodiments can be practiced. In
one preferred embodiment at least two separated fluid streams
include a predominately liquid stream and a predominately gas
stream. Embodiments of the tool have shown an ability to separate
out from a liquid/gas mixed phase a liquid stream that contains
less than 5% gas by volume in the liquid stream.
Preferred embodiments have also shown an ability in tests to
separate out at least one fluid stream with a head pressure loss
through the tool of less than 10% of the tool to wellbore pressure
differential.
In the disclosed embodiment the centrifugal accelerating occurs
subsequent to the establishment of annular flow. This is not
totally necessary. The embodiment disclosed sequentially performed
the steps of establishing annular flow, centrifugally accelerating
and then receiving into a chamber of gradually expanding
cross-sectional area of flow. The embodiment performed well.
However, one of skill in the art would realize that the stages
could be overlapped or the steps could be performed to a certain
extent simultaneously.
The invention includes apparatus for separating fluids flowing in a
downhole passageway in a well. One aspect of the apparatus includes
a pump attached at the surface to tubing attached to a downhole
well assembly where at least a portion of the downhole assembly
defines a fluid passageway. At least one vane is attached within a
passageway defined by at least a portion of the downhole assembly,
the vane passageway being in fluid communication with the pump.
Means are provided, in fluid communication with the vane
passageway, for separating centrifugally accelerated fluid by
density into at least two fluid streams.
In regard to means for separating centrifugally accelerated fluid,
the prior art teaches a great variety of alternate designs for
separating centrifugally accelerated fluids into at least two
streams. The selection of the most appropriate means is a matter of
design choice. The choice would likely relate to the prime uses for
the device. The instant structure disclosed for performing the
separation should be recognized as just one of many different
designs known. Selection of individual means is best left to
estimates of the prime use for the apparatus and the prime use for
the separated streams.
A further aspect of the apparatus of the invention includes at
least one vane attached within a passageway defined by at least a
portion of a downhole well assembly, together with a chamber in
fluid communication with the vane passageway where the chamber
defines a flow path having a cross-sectional area of flow that
gradually increases. A third aspect of the apparatus of the present
invention includes at least one vane attached within a passageway
defined by at least a portion of downhole assembly where the vane
has a pitch angle graduating from low to high in the direction of
flow. A fourth aspect of the apparatus includes a portion of a
downhole assembly defining an annular passageway. Preferably the
annular passageway defines a flow path having a cross-sectional
area of flow with an average radius greater than 75% of the annular
passageway radius. A fifth aspect of the invention includes a
portion of a downhole assembly defining an annular passageway
wherein the annular passageway has gradually increasing annularity
in a direction of fluid flow.
Various combinations of the above apparatus embodiments or aspects
may be constructed. In one preferred embodiment the vane passageway
is located in the downhole assembly downstream of the entry to the
annular passageway. Further, in preferred embodiments the apparatus
is less than three feet long; the annular passageway of gradually
increasing annularity is achieved by locating a diverging tapered
barrier, or cone, within a passageway; and the chamber having an
increasingly larger cross-sectional area of flow is achieved by
locating a tapered barrier, or cone, in that passageway, the taper
converging in the direction of flow. In general, as the
cross-sectional area of a tapered barrier or cone decreases, the
cross-sectional area of flow in a passageway surrounding the
barrier increases, and vice versa.
A further aspect of the present invention includes a method for
operating a downhole assembly with tubing, preferably coiled
tubing, that comprises pumping a fluid mixture down tubing to a
downhole assembly, separating the fluid mixture downhole by density
into at least two fluid streams and using at least one fluid stream
with a downhole assembly tool. In preferred embodiments the
downhole assembly tool might be a downhole assembly motor or a
downhole assembly jetting tool. The method might also include
venting at least one fluid stream to the wellbore. In some
embodiments the separating of fluids will separate the fluid
mixture into a predominately liquid stream and a predominately gas
stream. The invention also includes apparatus for use downhole in a
well comprising tubing, preferably coiled tubing, attached to a
downhole assembly, a pump attached at the surface to the tubing and
a fluid separator associated with the downhole assembly, the fluid
separator being operable to separate by density the fluid mixture
pumped down the tubing into at least two fluid streams. Preferably
the apparatus includes a tool associated with a downhole assembly
in fluid communication with at least one separated fluid stream.
The tool may comprise a downhole motor or a downhole jetting tool.
Preferably the fluid separator is a centrifugal separator.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than set
forth above will become apparent when consideration is given to the
following detailed description thereof. Such description makes
reference to the annexed drawings wherein:
FIGS. 1A and 1B illustrate a preferred embodiment of a fluid
separator in accordance with the present invention, in cutaway.
FIG. 2 is an elevational view of a portion of the preferred
embodiment of the fluid separator, the portion illustrating
vanes.
FIGS. 3A, 3B, 3C and 3D illustrate dimensions of the preferred
embodiment.
FIGS. 4A and 4B illustrate apparatus and method of use of the
present invention.
FIGS. 5 and 6 comprise charts of shop test results.
FIG. 7 is a table of numerical simulation data.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the instant apparatus, which was designed
particularly for the separation of a liquid/gas mixture downhole
and for test purposes, is illustrated in FIGS. 1-3. The embodiment
comprises a cylindrical outer housing 1, as illustrated in FIG. 1.
The cylindrical outer housing 1 has cylindrical bore 2 and a
tapered barrier, or conical flow diverter 3, at the entrance to
housing 1 creating a flow path, left to right, of gradually
increasing annularity. A set of turning vanes 8, illustrated in
FIG. 2, are attached to a body portion 9 of a base element located
within passageway 4 defined by bore 2 of housing 1. The base
element includes entry conical flow diverter 3, a body portion 9
having vanes 8 and transition cone 5, also referred to as a tapered
barrier, located downstream of turning vanes 8. Transition cone 5
creates a flow path of gradually increasing cross-sectional area.
Turning vanes 8 introduce swirl to, or centrifugally accelerate,
fluid flowing through passageway 4 in housing 1 from left to right.
The vanes are structured with an increasing pitch angle to increase
the rate of centrifugal acceleration in the direction of flow.
Transition cone 5, downstream of turning vanes 8 (in the preferred
embodiment there are five turning vanes) gradually increases the
cross-sectional area of flow of the centrifugally accelerated
fluid. FIG. 7 illustrates the results of a numerical simulation of
the effect of increasing the flow path area. Interesting results
can be seen in the swirl direction figure and acceleration
figure.
A first fluid or lighter fluid extraction port 6 is centered
downstream in housing 1 for collecting the lighter fluid stream
which would migrate by density toward the center of the passageway.
Bypass sub 7 routes the heavier fluid stream which would migrate
toward the outer periphery of bore 2 onward to the rest of the
downhole assembly. Bypass sub 7 also permits venting the first
fluid to the wellbore through vent ports 13. Alternate embodiments
might retain the lighter fluid and route it along a path parallel
to the heavier fluid phase.
Extraction port 6 and bypass sub 7 form one means for separating
centrifugally accelerated fluids, such as gas and liquid, by
density into at least two streams. Those familiar with centrifugal
separators will be familiar with other design choices for
separating into two streams of centrifugally accelerated fluid. The
intended application should dictate the design choice of the
separation means.
The "annularity" of the downhole passageway increases, and
increases smoothly and gradually, in the disclosed embodiment as
fluid flows over diverter 3 from left to right. A passageway of
increasing annularity is created, being a passageway whose
cross-sectional area of flow has an increasing average radius. The
notion of "average" radius is discussed above.
The flow path through turning vanes 8 disclosed in FIGS. 1A and 1B
comprises a relatively narrow annular passageway. The maximum
dimensions of the passageway are limited by the general
restrictions upon the design of the downhole tool. The annular
passageway tends to maximize the average radius at which swirl, or
centrifugal acceleration, is induced so that correspondingly the
annular velocity imparted to the fluid tends to be maximized. Tests
have shown that accelerations of between 1,000-2,000 gs can be
achieved over the design range of flow conditions for embodiments
such as that illustrated. Higher acceleration should result in more
rapid phase separation. The average radius at which swirl is
induced, indicated as radius 11 in FIGS. 1A and 1B, is preferably
greater than 75% of the radius of the annular passageway. The
radius of the passageway is the distance between axial center line
10 and the inside of housing 1 defining bore 2. This radius is
identified as radius 12 in the drawing in FIGS. 1A and 1B.
FIGS. 3A-3D illustrate relative dimensions of a preferred
embodiment for a downhole separator turning vane module. The
preferred material would be stainless steel.
FIG. 2 illustrates the pitch angle of the vanes of a preferred
embodiment of the present invention. If the pitch angle is defined
as the angle between a tangent to the vane and the longitudinal
direction of flow through the passageway, e.g. line 10, then FIG. 2
illustrates that the vanes of the preferred embodiment have an
initial pitch angle of approximately 0.degree. and a final pitch
angle of approximately 60.degree.. The turning vane profile
comprises a variable pitch helix offering an essentially axial flow
direction at entry. The vane defines a high discharge angle and
requires an axial length of only approximately 1/10th of the
overall length of the tool. The vane of the preferred embodiment
has been shown to generate high swirl rates, or high centrifugal
acceleration, with minimal pressure drop. Prior art devices teach
to the contrary, namely full length low pitch vanes which span
nearly the full diameter of the device and suffer from higher
pressure drops, greater overall length and lower separation
efficiencies.
Concentric extraction port 6, as illustrated in FIGS. 1A and 1B
channels the fluid of lesser density, such as gas, out of the fluid
phase separation chamber, without an initial direction change. This
enhances stability and minimizes remixing of the fluids. The
preferred embodiment vents this lower density fluid or gas to the
wellbore by two identical vent ports 13 which are located
diametrically opposite to each other to avoid lateral thrust on the
tool. Orifice diameter can profitability be varied to accommodate
different operating conditions such as wellbore
temperature/pressure, bottomhole assembly pressure drop, liquid and
gas mass flow rates, etc. Orifice replacement should be a simple
task, external to the tool. Preferably internal surfaces in contact
with fluid flow are machined to a high finish and all direction
changes are gradual. Use of the tapered or conical barriers,
diverter 3 and transition cone 5, accomplish gradual changes in
cross-sectional area of flow in the preferred embodiment. Such
gradual directional changes minimize turbulence, induced pressure
drop and phase remixing.
A computer model was developed and used to design the 13/4 inch
prototype tool illustrated in FIGS. 1-3. Results of the model study
are illustrated in the table of FIG. 7. Shop tests were then
conducted of an actual prototype under flow rate and pressure
conditions suitable for jetting. Shop test results are illustrated
in the graphs of FIGS. 5 and 6. The shop tests established that
basic tool performance was in good agreement with computer
modeling. Shop tests indicated that gas carryover into the liquid
stream and liquid loss with the gas discharge stream could be as
low as 3% of the original gas and liquid volumes respectively. Tool
pressure drop was generally below 25 psi. The overall tool length
of 30 inches proved satisfactory. A larger diameter tool should
permit higher accelerations. The larger diameter should also permit
"over separation" of gas and liquid with extra liquid being dumped
to the wellbore to enhance cuttings transport. Such a tool and
technique can remove existing volume flow rate limitations
associated with downhole motors, which would be particularly useful
in operations such as coiled tubing operations (but also may be
useful with similar operations using tubulars) and may, for
example, make it possible in drilling to independently optimize
both motor performance and cuttings transport more
satisfactorily.
Even though separation efficiency is quite high for the preferred
embodiment, it is clear that multiple stage designs could be
utilized, for instance in the event that gas leaving solution below
a first stage should become unacceptable.
A key aspect of the present invention is illustrated in FIG. 4.
FIG. 4 illustrates a method of using a fluid separator DFS with
tubing, such as coiled tubing CT, in a well bore WB. Bottomhole
assembly BHA locates downhole fluid separator DFS upstream
(considering the direction D of pumped fluid F) of motor M.
Downstream of motor M is further tool unit U. FIG. 4 illustrates
plural fluids F1 and F2 being pumped downhole through tubing CT.
Fluid separator DFS separates the fluids into portions F1 and F2.
FIG. 4 illustrates portion F2 continuing through motor M and
portion F1 being diverted to the annulus of wellbore WB. Upon the
surface coiled tubing CT is reeled from reel RL and injected into
wellbore WB with an injector 1 through well head WH. Fluids F1 and
F2 can be any fluid mixture separable by density. The tubing,
although illustrated as coiled tubing, could be tubulars or jointed
pipe.
While there are shown and described present preferred embodiments
of the invention, it is to be distinctly understood that the
invention is not limited thereto, but may be otherwise variously
embodied and practiced within the scope of the following claims.
ACCORDINGLY,
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