U.S. patent application number 12/810158 was filed with the patent office on 2011-02-03 for compact fluid disposal system and method for surface well testing.
Invention is credited to Francis Allouche.
Application Number | 20110023595 12/810158 |
Document ID | / |
Family ID | 40801585 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110023595 |
Kind Code |
A1 |
Allouche; Francis |
February 3, 2011 |
COMPACT FLUID DISPOSAL SYSTEM AND METHOD FOR SURFACE WELL
TESTING
Abstract
A compact fluid disposal and surface well testing system and
method, including a multiphase meter for flow-metering and sampling
of a received oil/gas/water stream and generating flow information
for the received oil/gas/water stream; a compact gas/liquid
splitter coupled to the multiphase meter and configured for
generating a gas rich stream, and a liquid rich stream from the
oil/gas/water stream based on the flow information from the
multiphase meter; and a free water knock out (FWKO)/holding tank
coupled to the compact gas/liquid splitter for receiving the liquid
rich stream from the compact gas/liquid splitter and degassing the
liquid rich stream and performing oil/water separation on the
liquid rich stream.
Inventors: |
Allouche; Francis; (Nogent
Sur Marne, FR) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE, MD 200-9
SUGAR LAND
TX
77478
US
|
Family ID: |
40801585 |
Appl. No.: |
12/810158 |
Filed: |
December 24, 2008 |
PCT Filed: |
December 24, 2008 |
PCT NO: |
PCT/US08/88314 |
371 Date: |
August 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61016542 |
Dec 24, 2007 |
|
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|
Current U.S.
Class: |
73/152.29 |
Current CPC
Class: |
G01F 15/08 20130101;
E21B 49/08 20130101; G01F 1/74 20130101 |
Class at
Publication: |
73/152.29 |
International
Class: |
E21B 47/10 20060101
E21B047/10 |
Claims
1. A compact fluid disposal and surface well testing system, the
system including: a multiphase meter for flow-metering and sampling
of a received oil/gas/water stream and generating flow information
for the received oil/gas/water stream; a compact gas/liquid
splitter coupled to the multiphase meter and configured for
generating a gas rich stream, and a liquid rich stream from the
oil/gas/water stream based on the flow information from the
multiphase meter; and a free water knock out (FWKO)/holding tank
coupled to the compact gas/liquid splitter for receiving the liquid
rich stream from the compact gas/liquid splitter and degassing the
liquid rich stream and performing oil/water separation on the
liquid rich stream.
2. The system of claim 1, further comprising a wet gas flare
coupled to the compact gas/liquid splitter for receiving the gas
rich stream from the compact gas/liquid splitter.
3. The system of claim 2, further comprising an oil burner coupled
to the compact gas/liquid splitter and the FWKO/holding tank for
receiving the liquid rich stream from the compact gas/liquid
splitter or an oil stream from the FWKO/holding tank via a transfer
pump therebetween.
4. The system of claim 3, wherein the FWKO/holding tank includes a
gas vent for venting gas that is degassed from the liquid rich
stream by the FWKO/holding tank.
5. The system of claim 4, wherein the FWKO/holding tank includes an
output for sending fluids from the liquid rich stream to a rig tank
or pit.
6. The system of claim 3, wherein the FWKO/holding tank further
includes an electro-coalescer for enhancing the purity of the water
separated from the liquid rich stream.
7. The system of claim 6, wherein the FWKO/holding tank further
includes an auto-adjustable floating smart weir for optimizing the
oil/water separation on the liquid rich stream.
8. The system of claim 5, wherein the system is used for a
beginning of a clean up phase of a well and effluent is directly
sent to a holding compartment of the FWKO/holding tank for
degassing purposes or flows through to the compact gas/liquid
splitter to handle gas pockets.
9. The system of claim 5, wherein the system is used for clean up
of a well in development and effluent is pre-separated through the
compact gas/liquid splitter, the liquid rich stream is sent to an
oil/water separation compartment of the FWKO/holding tank for
degassing and oil/water separation, wherein water is extracted from
a bottom of the FWKO/holding tank for disposal, and separated oil
is pumped and burned with the oil burner, and the gas rich stream
is sent to the wet gas flare.
10. The system of claim 5, wherein the system is used to stabilize
flow of a well, wherein the liquid rich stream includes less than
25% of water so that a resulting liquid is directly burnable
through the oil burner and the gas rich stream is sent to the wet
gas flare.
11. A method for fluid disposal and surface well testing system,
the method including: flow-metering and sampling of a received
oil/gas/water stream and generating flow information for the
received oil/gas/water stream with a multiphase meter; generating a
gas rich stream, and a liquid rich stream from the oil/gas/water
stream based on the flow information from the multiphase meter with
a compact gas/liquid splitter coupled to the multiphase meter; and
receiving the liquid rich stream from the compact gas/liquid
splitter and degassing the liquid rich stream and performing
oil/water separation on the liquid rich stream with a free water
knock out (FWKO)/holding tank coupled to the compact gas/liquid
splitter.
12. The method of claim 11, further comprising receiving the gas
rich stream from the compact gas/liquid splitter with a wet gas
flare coupled to the compact gas/liquid splitter.
13. The method of claim 12, further comprising receiving the liquid
rich stream from the compact gas/liquid splitter or an oil stream
from the FWKO/holding tank via a transfer pump with an oil burner
coupled to the compact gas/liquid splitter and the FWKO/holding
tank.
14. The method of claim 13, further comprising venting gas that is
degassed from the liquid rich stream with a gas vent of the
FWKO/holding tank.
15. The method of claim 14, further comprising sending fluids from
the liquid rich stream to a rig tank or pit with an output of the
FWKO/holding tank.
16. The method of claim 13, further comprising enhancing the purity
of the water separated from the liquid rich stream with an
electro-coalescer of the FWKO/holding tank.
17. The method of claim 16, further comprising optimizing the
oil/water separation on the liquid rich stream with an
auto-adjustable floating smart weir of the FWKO/holding tank.
18. The method of claim 15, further comprising beginning of a clean
up phase of a well, including directly sending effluent to a
holding compartment of the FWKO/holding tank for degassing purposes
or flowing effluent through to the compact gas/liquid splitter to
handle gas pockets.
19. The method of claim 15, further comprising performing clean up
of a well in development, including pre-separating effluent through
the compact gas/liquid splitter, sending the liquid rich stream to
an oil/water separation compartment of the FWKO/holding tank for
degassing and oil/water separation, extracting water from a bottom
of the FWKO/holding tank for disposal, pumping separated oil for
burning with the oil burner, and sending the gas rich stream to the
wet gas flare.
20. The method of claim 15, further comprising stabilizing flow of
a well, wherein the liquid rich stream includes less than 25% of
water, including directly burning the resulting liquid through the
oil burner, and sending the gas rich stream to the wet gas flare.
Description
CROSS REFERENCE TO RELATED DOCUMENTS
[0001] The present invention claims benefit of priority to U.S.
Provisional Patent Application Ser. No. 61/016,542 of Francis
ALLOUCHE, entitled "COMPACT FLUID DISPOSAL SYSTEM AND METHOD FOR
SURFACE WELL TESTING," filed on Dec. 24, 2007, the entire content
of which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to well testing, and
more particularly to a compact fluid disposal system and method for
surface well testing.
[0004] 2. Discussion of the Background
[0005] In surface well testing, the three main objectives are to
measure the volumetric flow-rate of individual phases, obtain
samples and determine characteristics of the main fluids, and
disposal off the effluents. In recent years, metering technology
has been developed to provide individual flow-rates without needing
any separation, thanks to the use of multiphase meters that can
measure the flow rate of the oil, gas and water in a oil well
effluent without the need for separation. However, there is still
no available solution to disposal of the effluents without
preliminary separation. For example, a separator is still required
to separate liquid from gas to burn oil and flare gas,
respectively. The separator is also needed when handling the
clean-up phase to extract water from oil, when the resulting liquid
is not burnable.
[0006] Accordingly, even in view of advances in the background art
systems, there is still a need for a compact fluid disposal system
and method for surface well testing.
SUMMARY OF THE INVENTION
[0007] The above and other needs and problems are addressed by the
exemplary embodiments of the present invention, which provide a
method and system for compact fluid disposal and surface well
testing. Accordingly, in exemplary embodiments a novel system and
method for fluid disposal for surface well testing applications are
provided. An exemplary global surface platform employs a multiphase
meter for metering and fluid sampling purposes. Downstream of the
multiphase meter is a disposal system made up of a compact high
pressure gas/liquid splitter and a combined low pressure free water
knock out (FWKO)/holding tank. The exemplary platform can be used
for the beginning of a well clean up phase, for clean up of a well
in development, and to stabilize flow of a well.
[0008] Accordingly, in an exemplary aspect of the present invention
there is provided a compact fluid disposal and surface well testing
system. The system includes a multiphase meter for flow-metering
and sampling of a received oil/gas/water stream and generating flow
information for the received oil/gas/water stream; a compact
gas/liquid splitter coupled to the multiphase meter and configured
for generating a gas rich stream, and a liquid rich stream from the
oil/gas/water stream based on the flow information from the
multiphase meter; and a free water knock out (FWKO)/holding tank
coupled to the compact gas/liquid splitter for receiving the liquid
rich stream from the compact gas/liquid splitter and degassing the
liquid rich stream and performing oil/water separation on the
liquid rich stream.
[0009] In another exemplary aspect of the invention, a method is
provided for a fluid disposal and surface well testing system,
which may be a compact system. The method includes flow-metering
and sampling a received oil/gas/water stream and generating flow
information for the received oil/gas/water stream with a multiphase
meter; generating a gas rich stream, and a liquid rich stream from
the oil/gas/water stream based on the flow information from the
multiphase meter with a compact gas/liquid splitter coupled to the
multiphase meter; and receiving the liquid rich stream from the
compact gas/liquid splitter and degassing the liquid rich stream
and performing oil/water separation on the liquid rich stream with
a free water knock out (FWKO)/holding tank coupled to the compact
gas/liquid splitter.
[0010] Still other aspects, features, and advantages of the present
invention are readily apparent from the following detailed
description, by illustrating a number of exemplary embodiments and
implementations, including the best mode contemplated for carrying
out the present invention. The present invention is also capable of
other and different embodiments, and its several details can be
modified in various respects, all without departing from the spirit
and scope of the present invention. Accordingly, the drawings and
descriptions are to be regarded as illustrative in nature, and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The embodiments of the present invention are illustrated by
way of example, and not by way of limitation, in the figures of the
accompanying drawings and in which like reference numerals refer to
similar elements and in which:
[0012] FIG. 1 illustrates a typical scenario of gas and liquid
flow-rate evolution against time for a well in development;
[0013] FIG. 2 illustrates a background art surface testing platform
based on a horizontal gravity separator;
[0014] FIG. 3 illustrates a background art flow mixer used as a
slug catcher;
[0015] FIG. 4 illustrates typical performance characteristics of
the flow mixer of FIG. 3;
[0016] FIG. 5 illustrates a background art vortex separator;
[0017] FIGS. 6-8 illustrate a background art low current-high
voltage electro-coalescer; and
[0018] FIGS. 9-17 illustrate an exemplary compact fluid disposal
system and method for surface well testing, according to the
present invention.
DETAILED DESCRIPTION
[0019] Various embodiments and aspects of the invention will now be
described in detail with reference to the accompanying figures.
Still other aspects, features, and advantages of the present
invention are readily apparent from the entire description thereof,
including the figures, which illustrate a number of exemplary
embodiments and implementations. Furthermore, the terminology and
phraseology used herein is solely used for descriptive purposes and
should not be construed as limiting in scope. Language such as
"including," "comprising," "having," "containing," or "involving,"
and variations thereof, is intended to be broad and encompass the
subject matter listed thereafter, equivalents, and additional
subject matter not recited.
[0020] During a well clean-up phase, liquid initially is placed in
temporary or permanent completion and a rate hole comes up at the
surface (referred to as Phase 1). For a well in development, it is
not rare to recover a large volume of completion fluids, which are
non-hydrocarbon fluids or a mixture of fluids which are not
burnable (referred to as Phase 2). The end of the clean-up is
reached when the gas-oil ratio (GOR) is stabilizing (referred to as
Phase 3). At this time the water flow-rate usually drops to zero
(or at least to a low flow-rate). Accordingly, FIG. 1 illustrates a
typical scenario of gas and liquid flow-rate evolution against time
for a well in development and for which a long cleanup phase,
producing large volume of non-hydrocarbons fluids at surface, is
needed before starting the usual flow-periods.
[0021] FIG. 2 illustrates a background art surface testing platform
based on a horizontal gravity separator. In FIG. 2, a surge tank is
usually made of two separate compartments. One is used as a tank
holder for mud or any fluids recovered at the very beginning of the
clean-up. These fluids need to be flashed and degassed through that
tank to be eventually dumped to rig tanks that can be offshore. The
second compartment is traditionally used as a buffer when the oil
flow-rate is very low during the transition zone between the end of
the clean-up and the beginning of the flow-period, but also for
calibration of oil flow-meters. Such calibration is referred to as
"combined meter factor," including both shrinkage and meter
calibration against oil density. In some applications, a steam
exchanger is often used to enhance separation, but also to prevent
gas hydrate formation at the choke level when there is some water
present.
[0022] Background art separation systems include centrifugal
systems that employ internal or external power and that are mainly
designed to separate oil from water with relatively high
efficiency. A flow mixer is a purely static device, including a
tank into which the multiphase flow is fed. Most of the dense part
of the fluid is drained from the bottom of the tank through an
ejector, while the least dense part is drained from the top and
directed via a pipe back to the ejector, where it is mixed with the
dense part of the fluid, according to the ejection ratio. FIG. 3
shows an existing flow mixer used as a slug catcher.
[0023] The performance of such a flow mixer can easily be adopted
to fit various requirements. FIG. 4 illustrates typical performance
characteristics of the flow mixer of FIG. 3. In FIG. 4, the typical
performance characteristics of the flow mixer over time are
illustrated by simulating a square-wave hold-up pattern 402 at the
inlet to the unit and with outlet gas volume fraction (GVF) 404 and
liquid levels 406 also plotted.
[0024] FIG. 5 shows a background art continuous flow separator that
simultaneously separates liquid/liquid, liquid/solid and
liquid/liquid/solid mixtures flowing through the separator at high
flow rates. In FIG. 5, the separator is a continuous flow turbo
machine that generates a strong centrifugal action or vortex
capable of separating light and heavy liquids, such as oil and
water, or any other combination of liquids and solids, at extremely
high flow rates. This separator accomplishes this separation
through the creation of a strong vortex in the flow, as the fluid
flows through the machine. In oil and water mixtures, this vortex
causes the heavier elements (e.g., water) to gravitate to the
outside of the flow and the lighter elements (e.g., oil) to move to
the center, which forms an inner core. If solids are present and
they are heavier than the liquid, they will be drawn to the outside
of the flow and follow the walls of the exit pipe or tube. The
stream exiting the machine will be divided, as shown in FIG. 5,
into two separate streams of the heavier liquid (e.g., water) and
lighter liquid (e.g., oil). As a result, separation is
achieved.
[0025] A vortex separator, while achieving separation, also acts as
its own pump, moving the fluid mixture through the machine. The
open design of the impeller blades makes the separator virtually
non-clogable. The centrifugal force generated by causing the flow
to rotate rapidly in a vortex about the centerline of the impeller
is the fundamental separation mechanism for a vortex separator. A
vortex separator is energy self-sufficient and provides its own
motive force.
[0026] FIGS. 6-8 illustrate a background art low current-high
voltage electrostatic coalescer to make oil-water separation more
efficient and cost-effective, and which is especially designed to
improve separation and the quality of the produced oil and water.
Separators often experience problems with emulsions and capacity
limits. An electrostatic coalescer (which may also be herein
referred to as "electro-coalescer") can enhance the speed and
efficiency of the separation process, by forcing small water
droplets in the oil continuous phase to merge and form larger,
faster sedimenting drops. However, this technology has so far been
unavailable for the turbulent conditions in the inlet
separator.
[0027] The use of an electrostatic coalescer greatly improves both
the oil and produced water quality, as shown in FIGS. 7-8. In
addition, the use of an electrostatic coalescer can provide
increased ability to separate heavy oil, improve produced water
quality, increase production, reduce emulsion breaker consumption,
improve process control, and reduce heating requirements.
[0028] Generally, the exemplary embodiments are directed to a novel
system and method for fluid disposal for surface well testing
applications. An exemplary surface platform employs a multiphase
meter for metering and fluid sampling purposes including
determining flow trends. Downstream of the multiphase meter is a
disposal system made up of a compact high pressure gas/liquid
splitter and a combined low pressure free water knock out
FWKO/holding tank, which will be described in more detail
hereinafter.
[0029] The exemplary platform can be used for the beginning of a
well clean up phase, wherein effluent is directly sent to a holding
compartment of the FWKO/holding tank for degassing purposes or
flows through to the compact gas/liquid splitter to handle gas
pockets.
[0030] The exemplary platform also can be used for clean up of a
well in development, wherein effluent is pre-separated through the
compact gas/liquid splitter, a liquid rich stream is sent to an
oil/water separation compartment of the FWKO/holding tank for
degassing and oil/water separation, water is extracted from a
bottom of the FWKO/holding tank for disposal, and separated oil is
pumped and burned with an oil burner (e.g., an EVERGREEN available
from Schlumberger), and the gas rich stream is sent to a wet gas
flare.
[0031] The exemplary platform can additionally be used to stabilize
flow of a well, wherein the liquid rich stream includes less than
25% of water so that a resulting liquid is directly burnable
through the oil burner and the gas rich stream is sent to the wet
gas flare. The exemplary platform, advantageously, enables a global
foot print reduction between 40-60%, as compared to background art
systems.
[0032] In terms of disposal, the flow envelope is about the same,
and potentially greater than the background art platforms,
especially for large gas flow-rates.
[0033] The term "system" may also be referred to herein as
"apparatus." Various advantages of the exemplary surface platform
in terms of cost, foot-print, flow envelope extensibility, and the
like, are further described. The exemplary platform can include
exemplary components, including the gas/liquid splitter, the
combination FWKO/holding tank, and a wet gas flare. The
FWKO/holding tank also can be referred to as a two phase separator,
i.e., it can separate oil and free water. It is usually a vertical
separator used mainly to extract any free water from oil for
disposal. Any gas entering the FWKO/holding tank is vented off. The
exemplary components are described, for example, in terms of
principle of operation, size, and weight, expected performance, and
the like.
[0034] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and more particularly to FIGS. 9-17 thereof, there
is illustrated an exemplary compact fluid disposal system and
method for surface well testing, according to the present
invention. In FIGS. 9-17, flow-metering and sampling is provided by
a multiphase meter 1902 (e.g., a PHASE-TESTER, or Vx TECHNOLOGY
available from Schlumberger) located upstream or downstream of a
choke manifold 1904 depending on the well head closing pressure. An
oil/gas/water stream 1932 is delivered from a flow head 1906.
Downstream of the choke 1904, there is provided a gas/liquid
splitter (GLSP) system 1908 operating at high pressure (HP) (e.g.,
up to 1400 psig, and with a minimum additional cost up to 2160
psig). The gas/liquid splitter system 1908 receives flow
information 1930 from the multiphase meter 1902 and separates a
multiphase stream 1910 from a well into separate streams, including
a gas rich stream 1912 sent to a wet gas flare 1914, and a liquid
rich stream 1916 sent to a second stage FWKO/holding tank 1918
operating at low pressure (LP) (e.g., 0 to 150 psig) or directly to
an oil burner 1920. The second stage 1918 further includes a gas
venting output 1927, an output 1922 to a rig tank or pit, e.g., for
water to the pit, over board rejection, storage tank or water
treatment system, and an output 1924 to a transfer pump 1926 that
transfers an oil stream 1928 to the oil burner 1920.
[0035] The gas/liquid splitter system 1908 can use the centrifugal
forces of the fluid, but in a further exemplary embodiment external
power, for example, supplied by an electrical motor, and the like,
can be employed. The gas/liquid splitter system 1908 can employ
similar principles as the vortex separator of the background art
(e.g., a Voraxial separator available from Enviro Voraxial
Technology, Inc.) or any other suitable continuous flow separator.
However, unlike the vortex separator of the background art, the
gas/liquid splitter system 1908 is configured for gas/liquid
separation instead of oil/water separation, and advantageously the
requirements in terms of separation efficiency can be much lower
(e.g., it is possible to accept a non-negligible volume of liquid
into the gas exit, and some gas bubbles into the liquid outlet). In
addition, the compactness, i.e., relatively small footprint of the
exemplary vortex-like system can be slightly undersized, as
compared to an application where the separation efficiency has to
be close to 100%. A further advantage is the relatively low
rotation speed of the impeller that can be employed with the
exemplary system, which helps to not induce too much shearing on
the liquid to facilitate the later oil/water separation via a
gravity effect.
[0036] Because of the very short residence time in the exemplary
gas/liquid splitter, controllability of the exemplary system should
also be achieved. A mixing system, for example, based on the
background art flow mixer designs can be placed upstream to dump
slugs and prevent the impeller of the GLSP from water hammering
effects. In addition, some real time flow-metering data coming from
the multiphase meter 1902 can be used to provide an efficient
forward control of the employed control valves. Further, except for
the very low gas flow rates, the wet gas flare 1914 can be capable
of accepting up to 30-40% of liquid, in mass ratio.
[0037] The second stage 1918 can be a vertical tank, operating at
low pressure (e.g., max 150 psig) for cost reasons, but also to
enable degassing of the liquid. The tank 1918 can basically have
the same configuration as known double compartment surge tanks.
However, the second stage 1918 includes some novel differences in
both the design and the mode of operation. For example, a first
compartment (e.g., of 50 BBL capacity) is provided and is
configured as a tank holder for early cleanup (e.g., mud and dirty
fluids in place in the completion and the rate-hole), as shown in
FIG. 17. The function of the first compartment is to hold dirty
fluids for degassing, before rejection into a rig tank (e.g.,
offshore) or eventually for burning later on, if the fluid is
burnable (e.g., offshore and on-shore). The fluid burn-ability also
can be estimated from the multiphase meter in real time
measurements for discriminating oil-based mud (OBM) from oil or
diesel.
[0038] A second compartment (e.g., 50 BBL capacity) is provided and
is configured as an oil/water vertical separator or so called free
water knock-out (FWKO). The purpose of such a compartment is to
extract as clean as possible aqueous fluid (e.g., water or brine)
and send the remaining stream 1924, which is mainly oil with less
than 25% water, to the oil burner 1920 via the transfer pump 1926.
A heating system also is included to raise the liquid temperature
and enhance the oil/water separation by reducing the oil viscosity.
In addition, an optional electro-coalescer system can be employed
(e.g., a background art electrostatic system, such as a VIEC-based
system, available from Aibel) to break emulsions and enhance
separation and enhance the purity of the extracted water.
[0039] Advantageously, as the liquid is being heated in the
oil/water separation stage, there is no need for a steam exchanger,
which is sometimes needed in a conventional setup, as centrifugal
forces applied in the first high pressure stage for gas/liquid
pre-separation are enough to drop the gas carry, even in case of
high liquid viscosity. However, an issue of gas hydrated formation
at the choke manifold level remains, in the case water is present
in the effluent. One option is to combine methanol/glycol injection
(e.g., traditionally used for shifting of the liquid/solid
equilibrium line) with kinetics retardants, and which
advantageously does not require a large volume to get a significant
effect.
[0040] FIGS. 10-12 further detail the exemplary mode of operation
of the exemplary surface platform 1900. In FIG. 10 is shown an
exemplary flow path at the beginning of the cleanup phase, for
example, when the fluids are in place in the completion (e.g.,
including oil-based mud (OBM), water-based mud (WBM), diesel, fresh
water or brine or solid loaded brine). At this stage there is
substantially no pressure or very low pressure and possibly large
liquid surge flow and even slugs. The effluent might be directly
sent to the holding compartment of the second stage 1918 for
degassing purposes or it could also flow through the GLSP-HP
(Gas/Liquid splitter) system 1908 to first safely handle gas
pockets. The gas/liquid separation energy (e.g., via rotation of
the impeller) in that case can be fully provided, for example, by
an electrical motor.
[0041] In FIG. 11 is shown an exemplary flow path after the
uploading sequence of fluids in place in the completion and partly
the rate-hole. This case is specifically addressing large clean-up
for wells in development, for example, when a large volume of water
based fluids (e.g., not burnable) have to be recovered at the
surface. In this case, the effluent is primarily pre-separated
through the gas/liquid splitter (GLSP-HP) system 1908. The liquid
rich stream 1916 is then sent to the oil/water separation
compartment of the FWKO-LP system 1918 for degassing and oil/water
separation. The water (e.g., with water purity basically of the
same order of magnitude as water extracted from a conventional
horizontal gravity separator) then is extracted from the bottom and
disposed in an appropriate manner. The separated oil 1924 (e.g.,
containing up to 25% of water) then is pumped as an oil stream 1928
by the transfer pump 1926 and burned with the oil burner 1920. The
gas rich stream 1912, for example, eventually including a large
quantity of liquid is sent to the wet gas flare 1914.
[0042] In FIG. 12 is shown the situation of an exemplary stabilized
flow-period. At this time, there is normally less than 25% of water
in the liquid rich stream 1916 so that the resulting liquid is
directly burnable through the oil burner 1920. There is also enough
gas and resulting pressure to counteract the back pressure induced
by the oil burner 1920. The gas rich stream 1912 can still be sent
to the wet gas flare 1914.
[0043] The following Table 1 compares the exemplary compact set-up
described with reference to FIGS. 9-12 with the background art
set-up described with reference to FIG. 2. Table 1 provides a
comparison in terms of foot print:
TABLE-US-00001 TABLE 1 Background Invention - Art setup with
Exemplary Foot Print Background Steam Compact Equipment m .times. m
[m2] Art setup Exchanger Setup Multiphase Meter 1 .times. 1 [1] X
Background art horizontal 5.68 .times. 2.24 [12.7] X X separator
Gas/Liquid Splitter 1.5 .times. 1.5 [2.25] X Combined FWKO/Tank 2.6
.times. 2.4 [6.24] X Surge Tank (2 .times. 50 BBL) 2.6 .times. 2.4
[6.24] X X Steam Exchanger 6.5 .times. 2.34 [15.21] X Choke
Manifold 1.84 .times. 1.78 [3.27] X X X Oil Transfer Pump 3.35
.times. 0.85 [2.84] X X X (PMP-EA 4000 BPD) Total 25.05 m2 40.26 m2
15.6 m2
[0044] Based on Table 1, depending on whether or not a steam
exchanger is employed with the conventional system (i.e.,
background art setup), foot-print reduction between about 39% and
about 62%, such as between about 40% and about 60% is achieved with
the compact setup of the invention.
[0045] Thus, the exemplary compact platform includes novel
features, including the combination of the multiphase meter 1902,
gas/liquid splitter system 1908, the wet gas flare 1914, the
combined FWKO/holding tank 1918, and the oil burner 1920. As
previously described, the exemplary gas/liquid splitter system 1908
includes a flow mixer, for example, used to minimize the effect of
sudden changes of gas volume fraction (GVF) and pressure
fluctuations, which typically occurs when the flow is slugging,
while also facilitating the system controllability.
[0046] The size of the liquid volume (or surge flow) in slug flow
conditions is fairly complex to determine, but can be estimated at
around 2 BBL. Typically, for example, a 2 BBL flow mixer is enough
to prevent a multiphase, multi-stage, centrifuge pump from slug
flow. The exemplary embodiments, however, can employ a smaller
mixer capacity (e.g., typically 1 BBL), for example, to increase
the robustness of the gas/liquid splitter system 1908 against slugs
due to low rotation speed and small impeller diameter, to minimize
the slug dampening so that the splitter remains controllable under
GVF and/or high dynamic flow-rate (e.g., this is related to the
speed of control valve actuation downstream of the splitter
outlets), and to provide for compactness.
[0047] FIG. 13 shows the exemplary G/L splitter 2500 of the
gas/liquid splitter system 1908, and which operates on a principle
of operation similar to that of the background art vortex-type
system. For example, similar to the vortex system, the exemplary
G/L splitter 2500 provides for a simple mechanical design with only
one part rotating impeller 2502 and with no dynamic vibration
induced by solid sticking of a rotating chamber, as used in
background art centrifuge systems. In addition, the impeller 2502
design prevents clogging (e.g., due to a large opening area), and
similar kind of flow (e.g., light fluid core with some
re-circulation) can be achieved as with the background art
vortex-type systems. Further, also provided are low electric power
consumption by an electric motor 2504, the possibility to add an
additional solid outlet if needed, and a light phase discharge pipe
with a fixed diameter (e.g., no adjustable weir with complex
cinematic need be employed).
[0048] Differences from the background art vortex-type system
include additional novel features of the G/L splitter 2500, such as
a multiphase mixture inlet 2506 that is tangential (e.g., to
minimize shearing), the electrical motor 2504 provided in an oil
chamber 2508 to obtain a pressure balanced dynamic sealing of a
shaft 2510 (e.g., retain pressure between the oil bath surrounding
the electrical motor and the separation chamber, which may also be
accomplished by a magnetic coupling) to reduce friction, and
increase the life time and prevent leaks, the re-use of parts
already designed for electrical submersible pumping (ESP, e.g.,
electrical motor, and impeller), and an automatic gas/liquid
interface control of the device. In addition, a feedback control
loop to react quickly is provided, including control valve
actuation via electric motorization. The G/L splitter 2500 also is
configured to separate gas from liquid by employing different
impeller and centrifuge forces, as compared to the background art
vortex-type system. A low rotation speed is used for the employed
diameter (e.g., typically 1800 rpm for a 4'' separation chamber),
and with a constant rotation speed to avoid use of a variable
frequency drive (VFD) and thus to advantageously reduce size and
cost. The G/L splitter 2500 further includes gas rich and liquid
rich stream outlets 2512 and 2514, respectively.
[0049] FIGS. 14-15 show an exemplary phase-frequency detector (PFD)
of the exemplary GLSP-HP system 1908, and including a flow mixer
2606 for providing output stream 2608 to the G/L splitter 2500. In
FIGS. 14-15, two motorized control valves 2602 and 2604 are placed
downstream of the gas rich outlet 2512 (producing a stream 1912)
and the liquid rich outlet 2514 (producing a stream 1916),
respectively. In an exemplary embodiment, electrical actuators are
employed instead of pneumatic actuators, advantageously, to obtain
quick reacting valves. An advanced controller system is provided,
for example, based on proportional-integral-derivative (PID)
regulation or a Neural network, and using the real time
flow-measurements delivered by the Vx meter.
[0050] In the exemplary system of FIGS. 14-15, no sub-system for
large size particle or metallic debris collection (e.g., typically
1 mm diameter or bigger) need be employed. However, in further
exemplary embodiments such a system can be employed to protect the
centrifuge from destructive impacts to the impeller, and to prevent
clogging of the liquid rich outlet 2514. In such an exemplary
embodiment, large damaging solids (e.g., solids above 1 mm
diameter) can be captured at the mixer level, by a slight
modification of its design, if need be. The exemplary system of
FIGS. 14-15 further includes a by-pass system 2702 and the
centrifuge 2500 motor housing 2704.
[0051] In an exemplary embodiment, the targeted flow-envelope of
the exemplary system can be the same or larger than that of the
background art systems (e.g., roughly 60 MMSCD & 6000 BLPD or
40 MMSCF & 15,000 BLPD @ 1440 psig).
[0052] In a first approximation, one can write:
G force = R .omega. 2 g ##EQU00001##
[0053] with
[0054] .omega. the rotation speed in rad/s
[0055] R the outer radius (m)
[0056] g the gravity acceleration in m/s.sup.2
[0057] The volume of the separation chamber is defined as:
Vol chamber = .pi. D 2 L 4 ##EQU00002##
[0058] The volume for the liquid ring and gas core will be
approximately and respectively:
Vol liquid = .pi. ( D 2 - D 0 2 ) L 4 and Vol gas = .pi. D 0 2 L 4
##EQU00003##
[0059] with D: The inside separation chamber diameter (m) [0060]
D.sub.0: the gas core diameter
[0061] The residence time of the liquid and the gas in the
separation chamber would respectively be:
T Res Liquid = Vol liquid Q liquid and T Res Gas = Vol gas Q gas
LineCondition ##EQU00004##
[0062] with Q.sub.liquid the liquid volumetric flow-rate (m/s) and
Q.sub.gas.sup.LineCondition the gas volumetric flow-rate at line
conditions (m.sup.3/s)
[0063] The average liquid droplet size entrained into the outlet
gas stream is calculated, as follows (e.g., based on the Stokes
law):
d liquid 2 = 0.5 D 0 T Res Gas 18 .mu. gas ( .rho. liquid - .rho.
gas ) g G force Avg - gas ##EQU00005##
[0064] The same calculation would apply to estimate the average gas
bubble size diameter entrained into the liquid outlet:
d gas 2 = 0.5 ( D - D 0 ) T Res Liquid 18 .mu. Liquid ( .rho.
liquid - .rho. gas ) g G force Avg - liq ##EQU00006## with G force
Avg - gas = 0.25 D 0 .omega. 2 g and G force Avg - Liquid = 0.25 (
D - D 0 ) .omega. 2 g ##EQU00006.2##
[0065] With the geometry and fluid properties reported in the two
next tables, one can estimate (at 1800 rpm) the size of the gas
droplets remaining in the liquid ring and conversely the size of
the liquid droplets remaining in the gas core.
TABLE-US-00002 TABLE 2 Geometry Centrifuge Internal Diameter D 4
Inch Gas Core diameter D.sub.0 3 Inch Tube length L 1 Meter
TABLE-US-00003 TABLE 3 Fluid properties Liquid Live density 750
Kg/m3 Liquid viscosity 10 Cp Gas specific gravity 0.6
Compressibility factor Z 0.99 Gas Temperature 60 deg C. Gas
viscosity 0.02 Cp
TABLE-US-00004 TABLE 4 Rotation speed 1800 rpm Qliquid (BLPD) 5000
15000 5000 15000 Qgas (MMSCFD) 10 10 60 60 Pressure (barg) 16 16
100 100 Vliquid (m/s) 2.6 7.8 2.6 7.8 Vgas (m/s) 49.2 49.2 49.7
49.7 Tresidence-liq (sec) 0.38 0.128 0.38 0.128 Tresidence-gas
(sec) 0.02 0.02 0.02 0.02 Tresidence-liq eqv 1 g (sec) 62 20 62 20
Tresidence-gas eqv 1 g (sec) 1.4 1.4 1.39 1.4 max gas droplet dia
into 71 123 74 128 liquid phase (microns) max liquid droplet dia
into 36 36 38 38 gas phase (microns) Vaxial/Vradial for gas 6.8 6.8
6.9 6.9 Vaxial/Vradial for liquid 0.36 1.08 0.36 1.08 Gforce
@gas/liquid interface 138
[0066] The above droplets sizes are not used to determine the
separation efficiency, but rather for enabling one to qualitatively
compare the separation efficiency of the invention's exemplary
system with the background art horizontal gravity separator.
Typically in the background art horizontal separator, the velocity
of the liquid and the gas are respectively 0.05 m/s and 0.5 m/s at
maximum capacity. With such velocities and the separator geometry
and its internal characteristics, one can estimate, for example, by
using Stokes law, that the liquid droplet sizes leaving the
exemplary separator from the gas outlet would be around 30 microns
or less. In the same manner, one can estimate that the size of the
gas droplets in the liquid leaving the exemplary separator from the
oil outlet would be around 400-500 microns (e.g., under the
assumption of a 10 cp oil viscosity) for 1 minute retention
time.
[0067] Comparing these droplet size numbers, one could determine
that the exemplary splitter can be able to better extract gas from
liquid (e.g., lower carry-under). On the other hand, the carry-over
would be pretty much the same. However, one can expect to have a
much larger carry-over because of the flow re-circulation inside
the gas core (e.g., as experimentally observed with a similar type
of splitter used to separate oil from water). This re-circulation
will increase the friction forces at the gas/liquid interface and
would probably tend to re-atomize some part of the liquid into the
gas core.
[0068] To be controllable, the gas/liquid interface needs to stay
in between acceptable limits. For example, the radius of the
interface has to be kept larger than the radius of the gas core
extraction tube and lower than the radius of the separation chamber
to avoid sending a large amount of gas into the liquid leg.
[0069] FIG. 16 shows an exemplary sensor system 2800 to locate the
gas/liquid interface, for example, based on capacitive
measurements. In FIG. 16, the exemplary sensor system 2800
includes, at an end of the separation tube 2500, shown in FIG. 13,
two annular perforated support plates 2802 supporting capacitive
electrodes or armors 2804. The separation tube 2500 includes a
separation chamber housing 2806. The housing 2806 and the gas rich
stream outlet (also referred to herein as "light phase extraction
pipe") 2512 are used as a support for the electrodes 2804. This
creates 4 cylindrical capacitive cells 2808, as shown in FIG.
16.
[0070] As shown in FIG. 16, the exemplary sensor system 2800 can be
configured with the following exemplary geometrical data, including
a length of the capacitor armor 2804 of 50 mm, a gap between R2 and
R3 of 5 mm, a gap between R1 and R2 of 3 mm, and a gap between R3
and R4 of 3 mm. Accordingly, one can compute the order of magnitude
of capacity to be measured based on the following table, as
follows.
TABLE-US-00005 TABLE 5 Fluid .epsilon..sub.r C.sub.liq (pf) C (pf)
C.sub.gas (pf) Gas 1 -- 18 16 Oil 2 110 36 -- Salty water 80 4405
1455 --
[0071] Assuming that the capacitor C.sub.liq will be full of liquid
and C.sub.gas full of gas (e.g., which can be cross-checked by
comparing C.sub.liq, C.sub.gas, and C), the gas/liquid interface
will be at radius R, so that R3<R<R4, and the following
exemplary algorithm can be employed:
[0072] Measure C.sub.liq
[0073] Calculate
r - liq = C liq 2 .pi. 0 H ln ( R 4 R 3 ) ##EQU00007##
[0074] Measure C.sub.gas
[0075] Calculate
r - gas = C gas 2 .pi. 0 H ln ( R 2 R 1 ) ##EQU00008##
[0076] Measure C
[0077] Calculate the position of the gas liquid/interface R:
C = C 1 C 2 C 1 + C 2 with C 1 = 2 .pi. 0 r - liq H ln ( R 3 R )
& C 2 = 2 .pi. 0 r - gas H ln ( R R 2 ) ##EQU00009##
[0078] So that:
ln R = [ 2 .pi. 0 r - liq r - gas H C ( r - liq - r - gas ) ] - ( r
- gas ln R 3 - r - liq ln R 2 ) ##EQU00010##
[0079] FIG. 17 further illustrates the combined FWKO/holding tank
1918 used as the exemplary low pressure second stage and using the
external geometry, for example, of a background art double
compartment (e.g., 2.times.50 BBL) surge tank. The novel features
include the internal design, and the way the vessel capacity is
used. In background art operation, there is one compartment
(eventually both) used as a holding tank for mud and dirty fluids
recovered at the beginning of the clean-up phase. This provides
retention time and enables the fluid degassing, which is mandatory
in case of rejection into rig tanks, for example. The second
compartment is traditionally used for shrinkage and oil flow meter
calibration (e.g., using the combined meter factor method), but
also as buffer for oil.
[0080] In the exemplary compact system of the invention, a first
compartment 2902 also is employed for early cleanup fluids
collection and degassing. In an exemplary embodiment, a volume of
50 BBL for the first compartment 2902 is sufficient to hold a
volume of fluid initially in place in the temporary completion and
the rate hole (e.g., 3000 ft long of 31/2'' ID tubing and which
gives a 35 BBL volume). In extreme cases, where the volume to be
recovered is larger than the compartment volume, the fluids can be
sent to a rig tank, with the surge tank compartment 2902 being
configured to provide a buffer capacity, while still enabling
degassing. Accordingly, the first compartment 2902 includes inlet
2904 (e.g., for diesel, OBM, WBM, completion fluid, solids from
wellbore cleanup) and outlets 2906 (e.g., for degassed diesel, OBM,
WBM, completion fluid, solids from wellbore cleanup for rig tank
storage, pit or burning via the oil burner), 2908 (e.g., solid
drain for holding tank) and 2910 (e.g., solid drain for FWKO), as
shown in FIG. 17.
[0081] A second compartment 2912 is configured as a vertical
oil/water separator (e.g., free water knock out). The separation
stage 2912 enables one to extract the water volume with an
oil-in-water content similar to what could be obtained from the
background art horizontal separator. The compartment 2912 also can
be used as a buffer for oil in the transition zone between the end
of the clean-up and the flow period, when the oil flow-rate can be
very low and below the minimum flow-rate required by the oil burner
1920. In an exemplary embodiment, in order to optimize the combined
oil buffer and oil/water separation compartment 2912 and to
unobtrusively monitor liquid levels, there is provided an
auto-adjustable floating smart weir 2914. The auto-adjustable
floating smart weir 2914 essentially comprises a radial collector
connected to a flexible tube/bellow, wherein one end is attached to
outlet 2926 of the compartment 2912. The auto-adjustable floating
smart weir 2914 is positioned just below the gas/liquid interface,
and adjusts automatically regardless of the position of the
gas/liquid interface on the oil/water interface. In addition,
inlet/outlet 2918 for steam heating (e.g., 10 Barg, 130.degree.
C.), bellows 2920, an optional electro-coalescer 2916 (e.g., an
electro-static type), outlets 2922 (e.g., for gas venting 1927),
2926 (e.g., for sending oil to the oil burner via the transfer pump
1926), and 2928 (e.g., for sending water to the pit, over board
rejection, storage tank or water treatment system), and inlet 2924
(e.g., for liquid (oil/water) from the gas/liquid splitter liquid
rich stream 1916) can be provided, as shown in FIG. 17.
[0082] In terms of oil/water separation efficiency, the combined
oil buffer and oil/water separation compartment 2912 is at least as
efficient as the background art horizontal separators. For example,
one can use settling theory to compare the oil/water separation
capability of the FWKO 2912 with the background art horizontal
separator. Specifically, with a density contrast of 200 Kg/m.sup.3
between oil and water (e.g., .rho..sub.oil=800 Kg/m.sup.3 and
.rho..sub.water=1000 Kg/m.sup.3), one can compute the following
minimum oil droplet size able to be raised up to the interface, as
shown in Table 6.
TABLE-US-00006 TABLE 6 Water Flow-rate 2000 4000 6000 Horizontal
Separator 150 mic 213 mic 261 mic FWKO 154 mic 218 mic 267 mic
[0083] Based on Table 6, one can conclude that the vertical FWKO
2912 can extract water with the same purity as the background art
horizontal separator, because although a vertical vessel is less
efficient than a horizontal vessel, the increased size of the
volume of the vertical vessel is much larger than that of the
horizontal vessel.
[0084] The exemplary operating mode of the FWKO 2912 can include an
oil/water interface (e.g., when present) being maintained
constantly at approximately one third of the bottom of the vessel,
and with the total liquid level (e.g., oil) varying between a low
and a high level (e.g., so as to be able to act as an oil buffer).
In addition, the separation compartment 2912 can be heated via a
low cost steam circulation coil or heat exchanger 2930 (e.g.,
employing SS316 1/2'' diameter tubing and approximately 25 meter
long). This heating capability, advantageously, can reduce the oil
viscosity and help the oil/water separation, especially for low oil
types (e.g., low API cases).
[0085] The following section provides some estimates of the heating
capability of the coil 2930. Assuming the following values:
[0086] Inlet liquid temperature: T.sub.fuild.sup.inlet=40 degC
[0087] Steam temperature: T.sub.steam=130 degC
[0088] Steam pressure: P.sub.steam=10 barg
[0089] One can compute the temperature increase .DELTA.T of the
oil-water mixture heated by the serpentine (e.g., clean tube), as
shown in Table 7.
TABLE-US-00007 TABLE 7 .DELTA.T (deg C.) Liquid Flow-rate Water Cut
(mixture) (BLPD) 95% 75% 50% 25% 1000 57 61 66 72 2000 36 39 44 50
3000 26 28 32 38 4000 20 22 26 30 5000 16 18 21 25
[0090] In an exemplary embodiment, the thermal energy transferred
from the steam to the liquid is 2.6 MBTU (753 kW), as compared to
the heat provided with a conventional steam exchanger of 4.3 MBTU,
and while also heating the gas.
[0091] As shown in FIG. 17, while not included as standard
equipment, but rather as an option (e.g., also not included in the
cost estimation above), the heating system 2930 can be combined
with the electro-coalescer module 2916 (e.g., a background art
electrostatic system) to deal with difficult emulsion cases.
[0092] Table 8 below summarizes the functions of the tank in the
background art set up and the exemplary invention compact
set-up.
TABLE-US-00008 TABLE 8 Background Art Setup Exemplary Compact Setup
Compartment 1 Holding tank for mud and dirty fluids Holding tank
for mud and dirty fluids Mud and dirty fluid degassing Mud and
dirty fluid degassing Compartment 2 During Clean-up During Clean-up
Holding tank for mud and dirty fluids Liquid degassing Mud and
dirty fluid degassing Oil buffer for burning via the oil burner Oil
buffer for burning via the oil burner (boosted with a transfer
pump) (boosted with a transfer pump) Water extraction from liquid
During Flow period Use for combined shrinkage effect and oil meter
calibration
[0093] Thus, the exemplary embodiments are directed to an exemplary
surface testing platform employing a multiphase meter for
flow-metering and sampling, and reducing the global foot-print from
about 40 to about 60%. The overall estimated cost is significantly
of the same order of magnitude as background art platforms based on
the horizontal gravity separator. In terms of flow-rate capacity,
the exemplary platform is able to handle up to 60 MMSCFD for gas
and 15,000 BLPD for liquid at a 1440 psig downstream choke pressure
(e.g., a slightly larger operating envelope than a background art
platform, in terms of disposal).
[0094] The exemplary platform introduces novel components,
including a compact gas/liquid splitter based on a vortex
technology (e.g., centrifugation via an impeller and separation in
a fixed wall chamber), a wet gas flare having a capability to
accept up to 30-40% of liquid in mass ratio, and a combined holding
tank/FWKO smart system. Gas/liquid pre-separation can be made at a
maximum pressure of 1440 psig. However, this maximum pressure can
be upgraded to 2160 psig with a reasonable extra cost (e.g., by
replacing 600 RF flanges with RTJ Class 900 flanges), boosting the
gas capacity by a factor 1.5 (e.g., 90 MMSCFD), and while
maintaining the same foot-print.
[0095] The exemplary gas/liquid splitter is based on a simplified
centrifuge system, having a small diameter and low rotation speed,
and thus being more reliable than background art systems based on
large cylinders rotating at high speed. In addition, the low
rotation speed can minimize the liquid shearing, while not creating
very fine dispersed droplets into the continuous phase.
[0096] The gas/liquid splitter system has a volume of 1 BBL while
providing a low hydrocarbon inventory at high pressure and while
improving safety. For high gas rate applications, two gas/liquid
splitters can be installed in parallel to handle up to 180 MMSCFD
(e.g., in such a case, an 88 mm multiphase meter can be
employed).
[0097] The exemplary compact platform can extract water with the
same oil-in-water content as background art platforms employing a
steam exchanger. However, with the heating at choke manifold level
being no longer able to ensure help for gas hydrate prevention, in
further exemplary embodiments, a combination of methanol/glycol and
kinetic retardant injection, instead of heating, can be
employed.
[0098] An exemplary way to manage the cleanup of this invention,
especially the uploading of the fluids in place in the completion
and the rate-hole when there is a lack of pressure, will foster the
use of this technology in industry. An additional
electro-coalescing system can be employed and can significantly
improve the purity of the extracted water during the clean-up
phase, facilitating the following water polishing step (if
needed).
[0099] All or a portion of the devices and subsystems of the
exemplary embodiments can be conveniently implemented by the
preparation of application-specific integrated circuits or by
interconnecting an appropriate network of conventional component
circuits, as will be appreciated by those skilled in the electrical
art(s). Thus, the exemplary embodiments are not limited to any
specific combination of hardware circuitry and/or software. In
addition, one or more general purpose computer systems,
microprocessors, digital signal processors, micro-controllers, and
the like, can be employed and programmed according to the teachings
of the exemplary embodiments of the present inventions, as will be
appreciated by those skilled in the computer and software arts.
Appropriate software can be readily prepared by programmers of
ordinary skill based on the teachings of the exemplary embodiments,
as will be appreciated by those skilled in the software art(s).
[0100] While the invention(s) have been described in connection
with a number of exemplary embodiments, and implementations, the
inventions are not so limited, but rather cover various
modifications, and equivalent arrangements, which fall within the
purview of the appended claims.
* * * * *