U.S. patent application number 12/355018 was filed with the patent office on 2009-07-30 for apparatus and methods for improved fluid compatibility in subterranean environments.
Invention is credited to Melissa Allin, Dennis Gray, Dealy T. Sears.
Application Number | 20090188312 12/355018 |
Document ID | / |
Family ID | 40897862 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090188312 |
Kind Code |
A1 |
Sears; Dealy T. ; et
al. |
July 30, 2009 |
Apparatus and Methods for Improved Fluid Compatibility in
Subterranean Environments
Abstract
A device for and method of testing fluid compatibility may
include placing a first fluid in a fixed-volume testing chamber and
placing a second fluid in a sample chamber. The method may also
include heating the fixed-volume testing chamber to about a
temperature of a subterranean environment and pressurizing the
fixed-volume testing chamber to about a pressure of the
subterranean environment. The method may further include
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a first rheology
value of the fluid within the fixed-volume testing chamber, moving
a portion of the second fluid from sample chamber into the
fixed-volume testing chamber, and determining, at a temperature and
pressure of about the temperature and pressure of the subterranean
environment, a second rheology value of the fluid within the
fixed-volume testing chamber.
Inventors: |
Sears; Dealy T.; (Comanche,
OK) ; Allin; Melissa; (Comanche, OK) ; Gray;
Dennis; (Comanche, OK) |
Correspondence
Address: |
JOHN W. WUSTENBERG
P.O. BOX 1431
DUNCAN
OK
73536
US
|
Family ID: |
40897862 |
Appl. No.: |
12/355018 |
Filed: |
January 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11524060 |
Sep 20, 2006 |
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12355018 |
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11211974 |
Aug 24, 2005 |
7128149 |
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11524060 |
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Current U.S.
Class: |
73/152.22 ;
73/152.27 |
Current CPC
Class: |
G01N 11/14 20130101;
C09K 8/42 20130101 |
Class at
Publication: |
73/152.22 ;
73/152.27 |
International
Class: |
E21B 47/06 20060101
E21B047/06 |
Claims
1. A method of testing fluid compatibility, comprising: placing a
first fluid in a fixed-volume testing chamber; placing a second
fluid in a sample chamber; heating the fixed-volume testing chamber
to about a temperature of a subterranean environment; pressurizing
the fixed-volume testing chamber to about a pressure of the
subterranean environment; determining, at a temperature and
pressure of about the temperature and pressure of the subterranean
environment, a first rheology value of the fluid within the
fixed-volume testing chamber; moving a portion of the second fluid
from the sample chamber into the fixed-volume testing chamber; and
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a second rheology
value of the fluid within the fixed-volume testing chamber.
2. The method of claim 1, comprising heating the sample chamber to
about the temperature of the subterranean environment.
3. The method of claim 1, comprising pressurizing the sample
chamber to about the pressure of the subterranean environment.
4. The method of claim 1, wherein the first fluid is a drilling
fluid and the second fluid is a spacer fluid.
5. The method of claim 1, wherein the first rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises approximately 100% first fluid.
6. The method of claim 1, wherein the second rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises approximately 95% first fluid and 5% second fluid.
7. The method of claim 1, wherein the first rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises approximately 100% first fluid; and wherein the second
rheology value is determined when the fluid within the fixed-volume
testing chamber comprises a portion of the first fluid and a
portion of the second fluid.
8. The method of claim 1, wherein the first rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises a percentage of the first fluid and a percentage of the
second fluid; and wherein the second rheology value is determined
when the fluid within the fixed-volume testing chamber comprises a
smaller percentage of the first fluid and a larger percentage of
the second fluid.
9. The method of claim 1, comprising: emptying the fixed-volume
testing chamber and the sample chamber; and repeating all steps
with the first fluid taking the place of the second fluid and the
second fluid taking the place of the first fluid.
10. The method of claim 1, comprising: moving a second portion of
the second fluid from the sample chamber into the fixed-volume
testing chamber; and determining, at a temperature and pressure of
about the temperature and pressure of the subterranean environment,
a third rheology value of the fluid within the fixed-volume testing
chamber.
11. The method of claim 10, wherein the third rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises approximately 75% first fluid and 25% second fluid.
12. The method of claim 10, comprising: moving a third portion of
the second fluid from the sample chamber into the fixed-volume
testing chamber; and determining, at a temperature and pressure of
about the temperature and pressure of the subterranean environment,
a fourth rheology value of the fluid within the fixed-volume
testing chamber.
13. The method of claim 12, wherein the fourth rheology value is
determined when the fluid within the fixed-volume testing chamber
comprises approximately 50% first fluid and 50% second fluid.
14. A method of testing fluid wettability, comprising: placing a
first fluid in a fixed-volume testing chamber; placing a second
fluid in a sample chamber; heating the fixed-volume testing chamber
to about a temperature of a subterranean environment; pressurizing
the fixed-volume testing chamber to about a pressure of the
subterranean environment; determining, at a temperature and
pressure of about the temperature and pressure of the subterranean
environment, a first rheology value of the fluid within the
fixed-volume testing chamber; determining, at a temperature and
pressure of about the temperature and pressure of the subterranean
environment, a first wettability value of the fluid within the
fixed-volume testing chamber; moving a portion of the second fluid
from the sample chamber into the fixed-volume testing chamber;
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a second rheology
value of the fluid within the fixed-volume testing chamber; and
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a second wettability
value of the fluid within the fixed-volume testing chamber.
15. The method of claim 14, comprising heating the sample chamber
to about the temperature of the subterranean environment.
16. An apparatus for testing fluid compatibility, comprising: a
fixed-volume testing chamber; a sample chamber in fluid
communication with the fixed-volume testing chamber; a heating
element for heating the fixed-volume testing chamber to about a
temperature of a subterranean environment; a stepper motor for
pressurizing the fixed-volume testing chamber to about a pressure
of the subterranean environment; and a viscometer for determining
rheology within the fixed-volume testing chamber.
17. The apparatus of claim 16, comprising a potentiometer for
determining wettability within the fixed-volume testing
chamber.
18. The apparatus of claim 16, comprising a controller for
regulating pressure of the sample chamber.
19. The apparatus of claim 16, comprising an actuator for continual
testing.
20. The apparatus of claim 16, comprising a casing; wherein the
fixed-volume testing chamber and the sample chamber are generally
contained within the casing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn. 119(e) from U.S. Provisional Patent Application No.
60/603,947, entitled "Apparatus And Methods For Improved Fluid
Displacement In Subterranean Formations," and filed on Aug. 24,
2004, the disclosure of which is incorporated herein by reference
in its entirety.
[0002] This application is a continuation in part of commonly-owned
U.S. patent application Ser. No. 11/524,060, filed Sep. 20, 2006,
entitled Apparatus and Methods for Improved Fluid Displacement in
Subterranean Formations" by James F. Heathman, et al., which is a
divisional patent application of commonly-owned U.S. Pat. No.
7,128,149, filed Aug. 24, 2005, entitled "Apparatus and Methods for
Improved Fluid Displacement in Subterranean Formations," by James
F. Heathman, et al., which are both incorporated by reference
herein for all purposes.
[0003] This application is also related to U.S. Pat. No. 7,128,142,
filed Aug. 24, 2005, entitled "Apparatus and Methods for Improved
Fluid Displacement in Subterranean Formations," the entirety of
which is herein incorporated by reference.
BACKGROUND
[0004] The drilling of well bores in subterranean formations
commonly involves pumping a "drilling fluid" into a rotated drill
string to which a drill bit is attached. The drilling fluid
typically exits through openings in the drill bit, inter alia, to
lubricate the bit and to carry cuttings up an annulus between the
drill string and the well bore for disposal at the surface. One
type of drilling fluid is an emulsion of substances that define a
non-aqueous external phase and an aqueous internal phase. In this
drilling fluid a non-aqueous "oleaginous" external phase (e.g., oil
or synthetic polymers) may be used to inhibit swelling of
water-sensitive drill cuttings (e.g., shale). Typical oil-based
drilling fluids contain some amount of an internal aqueous phase.
The emulsion often may be prepared by using an aqueous
(water-based) internal phase comprising salts (e.g., calcium
chloride). These oil- or synthetic-based drilling fluids also
typically include chemical emulsifying agents that act to form
oleaginous external phase emulsions, also known as "invert"
emulsions. These chemical emulsifying agents also promote the
oil-wetting of surfaces. This oil-wetted state promotes lubrication
of the drill bit and further stabilization of formation
materials.
[0005] After drilling is completed, a casing string commonly is
cemented in the well bore as part of completing the well. One type
of cementing operation includes placing a cement composition
through the casing string and into the annulus to displace the
drilling fluid from the annulus to the surface (however, flow in
the opposite direction may occur in some operations, such as in
reverse circulating or reverse cementing). A successful cementing
operation also includes bonding the cement composition with the
outer surface of the casing string and the inner surface of the
well bore defining the annulus.
[0006] The bond formed between the cement composition and the outer
surface of the casing string as well as the inner surface of the
well bore may not be optimal if the casing string and well bore
surfaces are not conducive to bonding with the cement composition.
For example, the non-aqueous portion of the drilling fluid may coat
the casing string and well bore surfaces. This may interfere with
the bonding of the cement composition to the surfaces, because the
aqueous cement composition generally will not bond readily with the
non-aqueous substances that may coat the surfaces. If improper or
incomplete bonding occurs at either of these surfaces, a thin
region called a "micro-annulus" may be formed. Formation of a
micro-annulus may lead to the loss of zonal isolation of the well
bore, and undesirable fluid migration along the well bore casing
string. Further, casing lifetime may be compromised if migrating
fluids are corrosive.
[0007] Conventional attempts to solve this problem have involved
displacement of the drilling fluid from the annular space between
the formation and casing string, or between an inner casing and an
outer casing strings so as to water-wet the formation and/or casing
surfaces. Accordingly, it often may be desirable for the
displacement fluid to invert the emulsion within the drilling
fluid, while water-wetting the formation and/or casing
surfaces.
[0008] A displacement fluid may be pumped ahead of the cement
composition to create water-wet surfaces. Certain embodiments of
such displacement fluids may cause a non-aqueous (hereafter
"oleaginous") external drilling fluid to invert, such that the
aqueous internal phase becomes external, and the oleaginous phase
becomes internal. Fluids that cause this inversion may be referred
to as "inverter fluids," and often may be suitable for use as
displacement fluids. Examples of suitable inverter fluids include,
inter alia, spacers and/or preflushes. Other nonlimiting examples
of suitable inverter fluids include settable fluids and other
compositions that comprise cementitious components such as
hydraulic cements. Other nonlimiting examples of suitable inverter
fluids are disclosed in, for example, U.S. Pat. Nos. 6,138,759,
6,524,384, 6,666,268, 6,668,929, and 6,716,282, the entire
disclosures of which are incorporated herein by reference.
[0009] Conventional inverter fluids typically comprise an aqueous
base fluid, viscosifying agents, and fluid loss control additives.
Certain inverter fluids also may comprise, inter alia, weighting
agents, surfactants, and salts. The weighting agents may be
included in an inverter fluid, inter alia, to increase its density
for well control, and to increase the buoyancy effect that the
inverter fluid may impart to the drilling fluid and filter cake
that may adhere to the walls of the well bore. Viscosifying agents
may stabilize the suspension of particles within the inverter
fluid, and may control fluid loss from the inverter fluid. The
presence of a surfactant in the inverter fluid may enhance the
chemical compatibility of the inverter fluid with other fluids
(e.g., the drilling fluid, and/or a cement composition that
subsequently may be placed against the formation) and may water-wet
downhole surfaces, thereby improving bonding of the cement
composition to surfaces in the formation, and may facilitate
improved removal of well bore solids. A salt may be included in the
inverter fluid, inter alia, for formation protection, improved
compatibility among fluids in the formation, and to desirably
affect wettability.
[0010] Inverter fluids also may be used to displace
oleaginous-external/aqueous-internal fluids from cased hole or open
hole well bores in operations other than cementing. One example
involves replacement of these inverter fluids with a completion
fluid (e.g., a solution of calcium chloride or bromide). This
operation may be conducted to clean the well bore for further
operations, such as perforation of the casing or, in the case of an
open hole, the onset of production of the well. In this case, the
inverter fluid may serve to displace the previous fluid and leave
the formation surfaces in a water-wet state.
[0011] The use of inverter fluids in cementing and other
subterranean operations often may be problematic, because of, inter
alia, difficulties in identifying a specific inverter fluid
composition that may desirably invert a particular drilling fluid
composition in a manner so as to water-wet the annulus to a desired
degree. Conventional attempts to identify specific inverter fluid
compositions that may desirably invert a particular drilling fluid
composition in a desired manner, at the temperature and pressure to
which both fluids may be exposed in a subterranean environment,
often have involved a multi-step process that may fail to identify
incompatibilities between components of the fluids at the
anticipated subterranean conditions. Commonly, a proposed inverter
fluid composition has been pre-conditioned to the anticipated
temperature and pressure using a high-pressure, high-temperature
apparatus, then cooled, de-pressurized, and removed from the first
apparatus, and placed in a testing apparatus at atmospheric
pressure and only slightly elevated temperature, along with a
sample of the drilling fluid that is to be inverted. This method is
problematic because it may mask certain changes or conditions
(e.g., cloud point changes, solubility changes, and the like) that
may result in an incompatibility between the fluids and/or that may
indicate that the proposed inverter fluid composition will not
invert a particular drilling fluid composition in a desired manner
at the desired temperature and pressure.
[0012] The accepted industry standard is to test compatibility of
fluids at 180.degree. to 190.degree. F. and at atmospheric
pressure, and assume that all greater pressures and temperatures
will be covered. Currently, the American Petroleum Institute (API)
recommends testing the rheologies of the following fluid ratios:
100% mud; 95% mud, 5% spacer; 75% mud, 25% spacer; 50% mud, 50%
spacer; 25% mud, 75% spacer; 5% mud, 95% spacer; and 100% spacer.
This normally requires that seven different fluids be prepared and
then measured. This allows for cooling of the fluids during mixing,
which may alter the outcome of the tests. Pending API Recommended
Practice 10B-2 recommends starting at 100% mud and slowly mixing
spacer at all ratios possible. However, this pending standard
indicates atmospheric pressure and ambient temperature.
SUMMARY
[0013] The present invention relates generally to subterranean
operations involving multiple fluids within a subterranean
environment. More particularly, the present invention relates to
apparatus and methods for determining fluid compatibility in
certain subterranean operations.
[0014] In one embodiment, a method of testing fluid compatibility
may comprise placing a first fluid in a fixed-volume testing
chamber, placing a second fluid in a sample chamber, heating the
fixed-volume testing chamber to about a temperature of a
subterranean environment, pressurizing the fixed-volume testing
chamber to about a pressure of the subterranean environment;
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a first rheology
value of the fluid within the fixed-volume testing chamber, moving
a portion of the second fluid from sample chamber into the
fixed-volume testing chamber, and determining, at a temperature and
pressure of about the temperature and pressure of the subterranean
environment, a second rheology value of the fluid within the
fixed-volume testing chamber.
[0015] In another embodiment, a method of testing fluid wettability
may comprise placing a first fluid in a fixed-volume testing
chamber, placing a second fluid in a sample chamber, heating the
fixed-volume testing chamber to about a temperature of a
subterranean environment, pressurizing the fixed-volume testing
chamber to about a pressure of the subterranean environment,
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a first rheology
value of the fluid within the fixed-volume testing chamber,
determining, at a temperature and pressure of about the temperature
and pressure of the subterranean environment, a first wettability
value of the fluid within the fixed-volume testing chamber, moving
a portion of the second fluid from sample chamber into fixed-volume
testing chamber, determining, at a temperature and pressure of
about the temperature and pressure of the subterranean environment,
a second rheology value of the fluid within the fixed-volume
testing chamber, and determining, at a temperature and pressure of
about the temperature and pressure of the subterranean environment,
a second wettability value of the fluid within the fixed-volume
testing chamber.
[0016] In one embodiment an apparatus for testing fluid
compatibility may comprise a fixed-volume testing chamber, a sample
chamber in fluid communication with the fixed-volume testing
chamber, a heating element for heating the fixed-volume testing
chamber to about a temperature of a subterranean environment, a
stepper motor for pressurizing the fixed-volume testing chamber to
about a pressure of the subterranean environment, and a viscometer
for determining rheology within the fixed-volume testing
chamber.
[0017] The features and advantages of the present invention will be
readily apparent to those skilled in the art upon a reading of the
description of the preferred embodiments, which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete understanding of the present disclosure and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings,
wherein:
[0019] FIG. 1 is a schematic and block diagram for an embodiment of
an apparatus of the present invention.
[0020] FIG. 2 is a schematic circuit diagram of a particular
implementation of a circuit for testing fluid in accordance with
the present invention.
[0021] FIG. 3 is a schematic and block diagram for an embodiment of
an apparatus of the present invention.
[0022] FIG. 4 is a flow chart illustrating an embodiment of a
method of the present invention.
[0023] FIG. 5 is a flow chart illustrating an embodiment of a
method of the present invention.
[0024] FIG. 6 is a side view of an apparatus in accordance with one
embodiment of the present invention.
[0025] FIG. 7 is a side view of an apparatus in accordance with
another embodiment of the present invention.
[0026] While the present invention is susceptible to various
modifications and alternative forms, specific embodiments thereof
have been shown in the drawings and are herein described. It should
be understood, however, that the description herein of specific
embodiments does not limit the invention to the particular forms
disclosed, but on the contrary, covers all modifications,
equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the appended claims.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] The present invention relates generally to subterranean
operations involving multiple fluids within a subterranean
environment. More particularly, the present invention relates to
apparatus and methods for determining fluid compatibility in
certain subterranean operations.
[0028] In certain embodiments of the present invention, methods are
provided for determining a suitable composition for a displacement
fluid. In certain embodiments of the present invention, the
displacement fluid may be an inverter fluid. Certain embodiments of
the methods of the present invention comprise using an apparatus of
the present invention to measure a value of a parameter related to
the electrical conductivity and/or rheological compatibility of an
initial mixture of (1) a test fluid having a composition nominally
equivalent to the oleaginous external/aqueous internal fluid in the
well and (2) part of a selected inverter fluid. In certain
embodiments, this may be done while simulating downhole conditions
for temperature and pressure. Certain embodiments of the methods of
the present invention also comprise adding a further portion of the
selected inverter fluid to the initial mixture, until the measured
value of the parameter indicates the test fluid has inverted from
an oleaginous-external/aqueous-internal state to an
aqueous-external/oleaginous-internal state. An alternative
embodiment tests the compatibility of various mixtures, such as
those set by the American Petroleum Institute (API).
[0029] Referring now to FIG. 1, illustrated therein is a schematic
and block circuit diagram for an embodiment of an apparatus of the
present invention. A fluid whose electrical conductivity and/or
rheological compatibility are to be tested is identified by the
reference numeral 100. Fluid 100 may be placed in fixed-volume
testing chamber 102. Generally, fixed-volume testing chamber 102 is
a pressure vessel. In certain embodiments of the present invention,
fixed-volume testing chamber 102 may be designed to withstand a
pressure of up to about 30,000 psi or greater at a temperature of
up to about 400.degree. F. or greater. For example, fixed-volume
testing chamber 102 may be a modified HPHT consistometer. In some
embodiments, a top port in fixed-volume testing chamber 102 may be
about 2 to 3 inches below a bottom of the lid, and slurry may
completely fill the chamber. Optional tube 104 may be placed in the
top port inside fixed-volume testing chamber 102 with a right angle
to take the top of tube 104 to the bottom of the lid allowing for a
more complete transfer, as indicated in FIGS. 6 and 7. Tube 104 may
allow fluid to be removed from just below the lid. In certain other
embodiments of the present invention, fixed-volume testing chamber
102 may be designed to withstand greater pressures at the same, or
greater, temperature. In certain preferred embodiments of the
present invention, fixed-volume testing chamber 102 includes a
stainless steel test cell with insulated electrodes and a silicone
encased heating jacket.
[0030] Within fixed-volume testing chamber 102, paddle 106 may be
disposed in fluid 100. In certain embodiments of the present
invention, paddle 106 may comprise a blender blade assembly. In
certain embodiments of the present invention, such blender blade
assembly may be a blade assembly typical of those used in
high-temperature, high-pressure cement consistometers. Paddle 106
may be rotated by electric motor 108, which, in certain embodiments
of the present invention, may comprise an AC or DC electric motor.
In certain embodiments of the present invention, electric motor 108
may be a direct drive motor, wherein a drive shaft (not shown)
penetrates fixed-volume testing chamber 102. In certain embodiments
of the present invention, electric motor 108 may be a magnetic
drive motor, wherein a drive shaft (not shown) does not penetrate
fixed-volume testing chamber 102, but instead drives a drive
sprocket or pulley 109 to rotate paddle 106. When a magnetic drive
motor is used, it may be capable of variable speed operation, and
rheological readings may be obtained at three or more speeds. In
certain preferred embodiments of the present invention, the speed
of electric motor 108 may be indicated in revolutions per minute
(rpm) on an indicator (not shown). When fluid 100 within
fixed-volume testing chamber 102 comprises a mixture of fluids
(such as, for example, a test fluid, a portion of an inverter fluid
to be tested, and any added substances), the stirring rate achieved
using electric motor 108 and paddle 106 may be sufficient to
quickly homogenize fluid 100, but not be so high that excessive
shear may affect readings and surfactant performance. Stirring may
cease for each fluid addition, and be restarted for rheological
determinations.
[0031] Thermocouple 112 may be disposed within fixed-volume testing
chamber 102, such that at least a portion of thermocouple 112 is
immersed in fluid 100. Two electrodes 114, 116 are immersed in
fluid 100 and connected to respective portions of the remaining
electrical circuit shown in FIG. 1. Electrodes 114, 116 are mounted
through, and insulated from electrical contact with, the side wall
of fixed-volume testing chamber 102, and are spaced
circumferentially (e.g., about 90.degree., but other spacing may be
used). As fixed-volume testing chamber 102 generally will comprise
metal, electrodes 114, 116 cannot be allowed to contact the
metallic walls of fixed-volume testing chamber 102, because
contacting the walls may result in erroneous operation. Electrodes
114, 116 may be made of any suitable conductive metals, including,
inter alia, iron, brass, nickel or stainless steel. The size of the
electrode surface is not critical; in certain preferred embodiments
of the present invention, the size of the electrode surface may be
about 0.2 square inches. Electrode 114 may connect to one terminal
of power source 118, and electrode 116 may connect to potentiometer
120 connected to another terminal of power source 118. Voltmeter
122 may be connected across potentiometer 120 to read a voltage
across potentiometer 120 in response to the conductivity of current
through fluid 100 from one electrode to the other. In certain
embodiments of the present invention wherein a measurement of the
gel strength is made, paddle 106 may be rotating at about 1/4 of
one degree per minute. In certain embodiments of the present
invention wherein a measurement of the apparent viscosity is made,
paddle 106 may be rotating at about 150 rpm. As will be noted later
with reference to FIG. 3, certain embodiments of the present
invention may employ ammeter 124 (shown in FIG. 2) instead of
voltmeter 122, wherein ammeter 124 may have the same effect as the
use of voltmeter 122, if the voltage across potentiometer 120 is
rectified and conditioned by components 126 in FIG. 2 connected to
ammeter 124.
[0032] The pressure within fixed-volume testing chamber 102 is
indicated by pressure indicator 110, and may be controlled by a
variety of means. Generally, the pressure within fixed-volume
testing chamber 102 will increase as fixed-volume testing chamber
102 is heated to a desired temperature. Additional pressurization
of fixed-volume testing chamber 102 may be achieved by injecting a
fluid from fluid supply 128 into fixed-volume testing chamber 102
via pump 130. This may be done manually or automatically. When a
fluid is injected into fixed-volume testing chamber 102 manually,
the pressure on pressure indicator 110 may be visually observed,
and pressure control valve 132 may be manually opened to permit
fluid to be pumped into fixed-volume testing chamber 102 through
pump 130. In the embodiment illustrated in FIG. 1, the pressure
within fixed-volume testing chamber 102 may be automatically
controlled. In certain of these embodiments wherein the pressure is
automatically controlled, pressure indicator 110 comprises a
pressure transmitter that sends signal 134 to pressure controller
136. Pressure controller 136 then may compare the pressure in
fixed-volume testing chamber 102 to a pressure set point, and may
send signal 138 to pressure transducer 140, which may send signal
142 to pressure control valve 132, thereby modulating pressure
control valve 132 (e.g., opening it) to permit pump 130 to inject
fluid from fluid supply 128 into fixed-volume testing chamber 102,
until the pressure in fixed-volume testing chamber 102 reaches a
desired value. Signal 138 may be an electrical signal, while signal
142 may be a pneumatic signal. Bleeder valve 144 optionally may be
provided on the piping between pump 130 and fixed-volume testing
chamber 102. A wide variety of valves may be suitable for use as
pressure control valve 132. A wide variety of controllers may be
suitable for use as pressure controller 136. In certain embodiments
of the present invention, pump 130 may be a pneumatic operated
piston pump. An example of a suitable diaphragm pump is
commercially available from Sprague Corp. In certain embodiments of
the present invention (not shown), pump 130 may be relocated such
that fluid supply 128 is located between pump 130 and fixed-volume
testing chamber 102. In these embodiments, fluid supply 128 may
comprise a pressure vessel, and pump 130 may cause fluid supply 128
to be pressurized to a desired pressure. In certain embodiments,
fluid supply 128 also may comprise a heating element, such as an
external heating jacket, internal heating coils, or the like, that
may heat fluid supply 128 to a desired temperature. Where fluid
supply 128 is used to pressurize fixed-volume testing chamber 102,
the fluid within fluid supply 128 generally will have a composition
that closely resembles the composition within fixed-volume testing
chamber 102 (e.g., where fluid 100 within fixed-volume testing
chamber 102 comprises a particular mixture of inverter fluid and
drilling fluid, the fluid within fluid supply 128 may have a
composition similar, or identical, to that of the particular
mixture of inverter fluid and drilling fluid).
[0033] The temperature within fixed-volume testing chamber 102 may
be controlled by a variety of means. In the embodiment illustrated
in FIG. 1, heating element 146 may be disposed within fixed-volume
testing chamber 102. In certain embodiments of the present
invention, heating element 146 comprises electrical heating coils.
In the embodiment illustrated in FIG. 1, heating element 146
receives electrical current from power supply 148 via conduit 150.
Temperature controller 152 receives signal 154 from thermocouple
112 that indicates the present temperature within fluid 100 in
fixed-volume testing chamber 102, compares the indicated
temperature to the desired temperature, and sends signal 156 to
power supply 148 that modulates the amount of current supplied by
power supply 148 so as to elevate, or decrease, the indicated
temperature. Signals 154 and 156 may be electrical signals. A wide
variety of controllers may be suitable for use as temperature
controller 152.
[0034] In certain embodiments of the present invention, receiving
tank 158 (shown in FIG. 3) may be provided, and may be connected to
fixed-volume testing chamber 102 to receive fluid 100 that may be
discharged from fixed-volume testing chamber 102. In certain
embodiments of the present invention wherein receiving tank 158 is
provided, receiving tank 158 generally will be a pressure vessel,
and may comprise a cooling element (not shown), such as cooling
coils, or the like, along with a number of optional elements such
as a temperature indicator (not shown), a pressure controller (not
shown), and the like.
[0035] Referring now to FIG. 3, a schematic diagram of a circuit
for testing a fluid in accordance with one embodiment of the
present invention is illustrated. One type of power source 118 is a
24-Vac source such as, for example, a STANCOR P8616 transformer
from Newark Electronics. A 24-Vac source is preferred, inter alia,
for safety purposes, but other alternating current power sources
may be used. Direct current sources also may be used, though they
are not preferred because electrophoretic mobility of ionic species
may cause plating at the electrodes, which may result in the loss
of the signal, or interference that may lead to inaccurate
measurement. Transformer 192 may be energized through on/off switch
160 (shown in FIG. 2) connectible to a suitable primary power
supply (e.g., a conventional power main).
[0036] Potentiometer 120, such as, for example, a Bourns
3S00s-2-102, sets the span of readings described below. In the
circuit illustrated in FIG. 2, an ammeter 124 (e.g., Monnteck
25-DUA-200-U from Allied) is used instead of a voltmeter. As noted
earlier with reference to FIG. 1, the use of an ammeter 124 may
have the same effect as the use of voltmeter 122, if the voltage
across potentiometer 120 is rectified and conditioned by components
126 connected to ammeter 124. Also shown in FIG. 2 is an optional
on/off indicating lamp 162 that illuminates when switch 160 is
closed to place the circuit in an operative state for testing in
accordance with the present invention.
[0037] FIG. 2 also illustrates an example of a heating element
control circuit that may be used in the apparatus of the present
invention. Temperature controller 152 may send a signal to power
supply (e.g., solid state relay) 148 that energizes, or
de-energizes the relay on and allows power to be sent to the
heating element through heat control switch (e.g., providing
heat).
[0038] The apparatus shown in FIGS. 1-2 measure the surface-acting
properties of the fluid 100 by measuring the voltage drop across
potentiometer 120 (measured either directly as a voltage in FIG. 1
or as a resulting current in FIG. 2). Normally, oleaginous-external
drilling fluids are not electrically conductive, in contrast to
aqueous-based inverter fluids, which are conductive. When
electrodes 114, 116 are coated with a stable, oleaginous-external
drilling fluid, the voltage drop across potentiometer 120 is zero
because no current (or an undetectable current) flows between
electrodes 114, 116. The maximum voltage drop, which may be
obtained when using a conductive inverter fluid by itself as fluid
100, will be some value above zero.
[0039] Referring now to FIG. 3, illustrated therein is an
alternative embodiment of an apparatus of the present invention. As
illustrated in FIG. 3, an inverter fluid reservoir may be provided,
and depicted by the reference numeral 164. Generally, inverter
fluid reservoir 164 is a pressure vessel. In certain embodiments of
the present invention, inverter fluid reservoir 164 may be designed
to withstand a pressure of up to about 30,000 psi or greater at a
temperature of up to about 400.degree. F. or greater. In certain
other embodiments of the present invention, inverter fluid
reservoir 164 may be designed to withstand greater pressures at the
same, or greater, temperature. In certain embodiments of the
present invention, inverter fluid reservoir 164 may comprise
heating element 166. Inverter fluid reservoir 164 may be
pressurized by pump 168, which is supplied with inverter fluid (or
another compatible fluid) through reservoir 170. When a quantity of
inverter fluid is desired to be introduced into fixed-volume
testing chamber 102 (which generally will already comprise a
drilling fluid to be tested, and which will, in certain embodiments
of the present invention, already be at elevated temperature and
pressure), valves 132, 172, 174, and 176 may be opened (if each is
not already in an open position), and a desired amount of inverter
fluid may be introduced into fixed-volume testing chamber 102. In
some embodiments, a spacer fluid may enter the bottom of
fixed-volume testing chamber 102, as indicated in FIG. 1, to take
advantage of the typical situation where the spacer is heavier than
the corresponding drilling fluid.
[0040] As illustrated in FIG. 3, receiving tank 158 may be provided
to receive fluid from flowing out of fixed-volume testing chamber
102 when the inverter fluid is being injected. Generally, receiving
tank 158 is a pressure vessel. In certain embodiments of the
present invention, receiving tank 158 may be designed to withstand
a pressure of up to about 30,000 psi or greater at a temperature of
up to about 400.degree. F. or greater. In certain other embodiments
of the present invention, receiving tank 158 may be designed to
withstand greater pressures at the same, or greater, temperature.
Generally, valve 179 may be included in the flow line between
receiving tank 158 and fixed-volume testing chamber 102, so as to
isolate receiving tank 158 from fixed-volume testing chamber 102
when desired. In certain embodiments of the present invention,
receiving tank 158 may comprise cooling element 180 (e.g., cooling
coils). The cooling of the fluid in receiving tank 158 allows a
portion of the fluid to be removed from receiving tank 158 for
evaluation of the fluid at atmospheric pressure and temperatures
less than about 190.degree. F., and also for future testing.
[0041] Optionally, as illustrated in FIG. 3, a surfactant reservoir
may be provided, and depicted by the reference numeral 182.
Generally, surfactant reservoir 182 is a pressure vessel. In
certain embodiments of the present invention, surfactant reservoir
182 may be designed to withstand a pressure of up to about 30,000
psi or greater at a temperature of up to about 400.degree. F. or
greater. In certain other embodiments of the present invention,
surfactant reservoir 182 may be designed to withstand greater
pressures at the same, or greater, temperature. In certain
embodiments of the present invention, surfactant reservoir 182 may
comprise heating element 184. Surfactant reservoir 182 may be
pressurized by pump 186, which may be supplied with surfactant (or
another compatible fluid) through reservoir 188. When a quantity of
surfactant is desired to be introduced into fixed-volume testing
chamber 102, valves 132, 174, 176, and 190 may be opened (if each
is not already in an open position), and a desired amount of
surfactant may be introduced into fixed-volume testing chamber
102.
[0042] Generally, a calibrating procedure may be performed before
the apparatus of the present invention is used. Before a test is
run, the voltage or current relative to potentiometer 120 may be
measured using meter 122/124 and only the
oleaginous-external/water-internal drilling fluid used as fluid
100. This reading should be zero since fluid 100 should be
nonconductive. A non-zero reading indicates the instrument is
malfunctioning (e.g., an electrical short occurring through the
instrument or electrodes 114, 116) or the
oleaginous-external/aqueous-internal fluid is contaminated with
water in the external phase. Alternatively, calibration may be done
first with the proposed inverter fluid and then with the
non-aqueous fluid. Next, after thoroughly cleaning testing chamber
102, the electrical parameter (voltage or current) may be measured
with only the proposed inverter fluid (e.g., no drilling fluid is
present) as fluid 100. This should give a non-zero reading through
meter 122/124, which corresponds to a maximum voltage drop because
the aqueous-based inverter fluid is electrically conductive.
Potentiometer 120 may be adjusted until a desired maximum reading
is obtained. Potentiometer 120 should not be adjusted after this
setting is obtained. Once the zero value of potentiometer 120 and
the maximum span value of potentiometer 120 have been determined
using suitable calibrating fluids, the precise moment when the
actual drilling fluid to be tested undergoes an external phase
change, or inversion (thus wettability) may be determined.
[0043] Generally, the composition of the test
oleaginous-external/aqueous-internal fluid may resemble the
particular drilling fluid that may be used in the subterranean
environment. In certain embodiments of the present invention, the
test fluid may be only nominally equivalent to the actual fluid
used (or that may be intended to be used) in the formation. As
referred to herein, the term "nominally equivalent" will be
understood to mean that the test fluid generally has the same
composition as the oleaginous-external/aqueous-internal drilling
fluid used during the drilling procedure, and that the test fluid
generally also may be pre-conditioned to a comparable temperature
and pressure to which the actual downhole fluid may be exposed.
Though the term "nominally equivalent" includes, but is not limited
to, exact identity between the fluids, the term also embraces
slight differences in the test fluid and the drilling fluid (e.g.,
wherein the test fluid and the drilling fluid have different
electrolyte contents). In certain embodiments of the present
invention wherein the apparatus and methods of the present
invention test are used at a well site, the test fluid may comprise
a sample of a batch of the drilling fluid to be placed into the
well bore.
[0044] The initial inverter fluid compositions to be tested against
the test oleaginous-external/aqueous-internal fluid may be chosen
by experience in dealing with the inverter fluids as known by one
skilled in the art, with the benefit of this disclosure.
[0045] Generally, the drilling fluid to be used in the test will be
preconditioned by increasing its pressure and temperature according
to a desired schedule, until the drilling fluid reaches the
temperature and pressure to which it is expected to be exposed in
the subterranean environment. In certain embodiments of the present
invention, this will be the particular well's bottom hole
circulating temperature and pressure. In certain embodiments, the
preconditioning schedule will approximate the variations in
temperature and pressure to which the drilling fluid will be
exposed during at least a portion of its passage through the
subterranean environment. The drilling fluid may be preconditioned
within the apparatus of the present invention, or within any other
suitable apparatus. In certain embodiments of the present
invention, the various selected fluids to be used in the test
(e.g., the drilling fluid, the inverter fluid, and other fluids)
may be placed in an apparatus of the present invention, and
preconditioned therein by increasing their pressure and temperature
according to a desired schedule, until the fluids reach the
temperature and pressure to which the determined inverter fluid is
expected to be exposed in the subterranean environment (e.g., the
particular well's bottom hole circulating temperature and
pressure). In certain embodiments, the preconditioning schedule
will approximate the variations in temperature and pressure to
which the fluids will be exposed during at least a portion of their
passage through the subterranean environment. Such preconditioning
generally ensures the fluids are stable and all chemicals have been
conditioned.
[0046] After the calibration procedure described above has been
performed on potentiometer 120, and the drilling fluid and/or other
fluids to be tested have been preconditioned to a desired extent as
described above, the actual testing of the combination of inverter
fluid and oleaginous-external/water-internal drilling fluid may be
performed, using one or both of two procedures, as well as other
suitable procedures. The particular one(s) chosen may be based upon
prior knowledge of the drilling fluid system, and the inverter
fluids, including the behavior of the various surfactants. During
this procedure, viscosity spikes that may occur at specific
drilling fluid-to-inverter fluid and drilling fluid-to-surfactant
ratios also may be observed and reported.
[0047] In one procedure, the drilling fluid to be tested and the
selected inverter fluid may be mixed in a desired ratio (e.g.,
50:50). The selected inverter fluid may or may not contain one or
more surfactants when mixed with the drilling fluid. After the
mixture is made homogenous by mixing with paddle 106, and while
stirring of the mixture continues, one or more selected surfactants
may be injected into this embodiment of fluid 100, and the
electrical behavior may be observed through the response of meter
122/124. As the concentration of surfactants increases within this
mixture, the reading from meter 122/124 will start to increase as
the surfactants begin to invert the oleaginous-external drilling
fluid and clean the surfaces of electrodes 114, 116. During this
transition process, when the mixture of the inverter fluid and the
drilling fluid is in a bicontinuous phase (often referred to as a
Winsor Type III emulsion), the readings from meter 122/124 may
fluctuate, dropping to a stable minimum value at equilibrium when
the mixture homogenizes and the oil recoats the electrodes.
Eventually, the reading from meter 122/124 will reach a maximum
value equal to, or slightly greater than, that recorded for 100%
inverter fluid (e.g., wherein drilling fluid is absent) as the
fluid 100, thus indicating the electrodes are completely
water-wetted and the mixture is 100% water-external (e.g., the
drilling fluid has been inverted). The maximum reading may be
slightly above that obtained with 100% spacer (e.g., due to salts
dissolved in the aqueous phase of the drilling fluid). To ensure
that inversion has actually occurred, the maximum reading should
remain stable for a suitable length of time, such as twenty
minutes. If the reading decreases, the appropriate surfactant(s)
may again be added and the electrical response monitored until an
electrically stable fluid has been obtained. Once the electrically
stable fluid has been obtained, the concentration of the injected
inverter fluid ingredient(s) (e.g., the one or more surfactants in
this example) in the total mixture in fixed-volume testing chamber
102 may be determined. This total mixture includes the measured
initial mixture (e.g., the initial mixture of drilling fluid and
inverter fluid, in this example) plus the measured added portion of
the injected inverter fluid ingredients (e.g., the one or more
surfactants in this example). The concentration of the injected
inverter fluid ingredients in only the total inverter fluid itself
also may be readily determined. This concentration may be readily
determined because the volume of inverter fluid in the initial
mixture is known and the volume of added inverter fluid ingredients
(e.g., surfactants) is known from the injection. The procedure
described above is, of course, capable of numerous modifications,
including, inter alia, embodiments wherein the testing is performed
by mixing the drilling fluid to be tested along with a selected
inverter fluid that already comprises a desired amount of
surfactants.
[0048] In the second, alternative procedure, the inverter fluid
initially may be prepared with one or more surfactants. Instead of
injecting surfactant into an initial mixture of drilling fluid and
inverter fluid, the drilling fluid may be present in fixed-volume
testing chamber 102 without the inverter fluid, and then an
inverter fluid may be injected into the drilling fluid, so as to
determine the volume of inverter fluid required to invert the
drilling fluid to a desired degree. The reading on meter 122/124
may be observed, and once the maximum reading is obtained for the
suitable time period, the electrically stable fluid has been
obtained, thereby identifying the ratio of the inverter fluid to
the drilling fluid. That is, the total volume of the selected
inverter fluid in the initial mixture (if any) and the added
further portion of the selected inverter fluid are known or
determined and the ratio of the final volume of the inverter fluid
to the initial volume of the test
oleaginous-external/aqueous-internal fluid in the initial mixture
may be determined. The procedure described above is, of course,
capable of numerous modifications.
[0049] Having used the apparatus of the present invention to
determine parameters of the drilling fluid and inverter fluid, a
number of determinations may be made. For example, depending on the
viscosity profile of the drilling fluid, inverter fluid, and
mixtures thereof, it may be desirable to adjust the surfactant such
that the inversion from oleaginous-external to water-external
occurs at some specified drilling fluid-to-inverter fluid ratio.
For example, synthetic drilling fluids typically have a low yield
point; therefore, when the phase change occurs, the now
water-wetted solids of the drilling fluid may settle severely. This
may lead to bridging in downhole casing tools and in the annulus
when fluid velocities are insufficient to provide support. This
also may lead to annular solids bed deposition on the low side of
an inclined or horizontal well bore.
[0050] Conversely, some drilling fluid systems viscosify severely
when inverted, especially in the presence of an aqueous spacer.
Depending on where the viscosity peak occurs, it may be desirable
to shift the drilling fluid-to-inverter fluid ratio such that
inversion occurs away from the viscosity peak by adjusting the
surfactant. The injection procedure wherein one or more surfactants
are injected (rather than the entire inverter fluid) is best suited
to pinpointing the critical surfactant concentration. Once that
surfactant concentration is known, the inverter fluid injection
procedure may be repeatedly used with alternate surfactant
concentrations to find a drilling fluid-to-spacer ratio where
inversion occurs but with a lower viscosity spike.
[0051] A properly designed inverter fluid should have adequate
Theological properties to support solids released from the drilling
fluid system. In the case of a drilling fluid system that loses
solids-carrying capacity when it is inverted, it may be more
desirable to adjust (typically reduce) the surfactant loading such
that a higher percentage of inverter fluid is required to cause the
external phase of the resulting mixture to become water-wet. This
will result in more solids-carrying capacity, thus reducing the
risk of dropping solids as described above.
[0052] In one embodiment of a method of the present invention, a
method of designing an inverter fluid is provided that comprises
designing an inverter fluid that intermixes with the
oleaginous-external/aqueous-internal fluid to cause the
oleaginous-external/aqueous-internal fluid (or at least a coating
of this fluid on the outer surface of the tubular string or on the
wall of the well bore) to invert. Designing the inverter fluid
includes testing a selected inverter fluid with a test fluid having
a composition nominally equivalent to the composition of the
oleaginous-external/aqueous-internal fluid.
[0053] Once the desired inverter fluid has been designed, certain
embodiments of the methods of the present invention further
comprise making a quantity of the designed inverter fluid to be
placed in the annulus of the well. This quantity may be placed in
the well for inverting the oleaginous external/aqueous-internal
fluid actually in the well on at least a portion of one or more
surfaces of the annulus. One technique for placing the inverter
fluid includes pumping the quantity of inverter fluid in the well
along with a quantity of a cement composition such that the present
invention also encompasses a method of cementing a well in addition
to merely water wetting the well. In this application, the inverter
fluid precedes the cement composition such that the pumped inverter
fluid displaces at least part of the
oleaginous-external/aqueous-internal fluid in the annular region
and inverts the coating of oleaginous-external/aqueous-internal
fluid sufficient to remove the coating ahead of the cement
composition. At least part of the pumped inverter fluid may be
subsequently displaced by the cement composition to obtain bulk
cement displacement, but without an undesirable micro-annulus.
Pumping of the fluids may be performed in a conventional or
otherwise known manner (such as reverse-circulating or reverse
cementing, for example).
[0054] Another technique for placing the inverter fluid includes
pumping the quantity of inverter fluid in the well followed by a
quantity of a completion fluid. Examples of completion fluids may
include, for example, fresh water, along with aqueous salt
solutions (e.g., brines). A broad variety of aqueous salt solutions
may be suitable for use as completion fluids in certain
embodiments, including, for example, solutions that comprise
calcium chloride, sodium chloride, potassium chloride, calcium
bromide, zinc bromide, and formate completion brines (e.g., cesium
formate, potassium formate, and the like); other aqueous salt
solutions also may be suitable. In this technique, displacing and
inverting with the inverter fluid, and ultimately replacing the
oleaginous-external fluid and the inverter fluid with the
completion fluid prepares the well bore for future operations.
[0055] The testing and the making steps referred to above may be
performed at the well or elsewhere (e.g., at a laboratory for the
former and a manufacturing facility for the latter). The testing is
in accordance with further aspects of the present invention
described below. Making the designed inverter fluid may be
performed in a conventional manner given a particular design
obtained from the testing of the present invention. For example, in
certain embodiments, the aqueous inverter fluid may be prepared at
the well site. Mixing water may be measured into a field blender.
Defoaming agents may be added, followed by a pre-blended dry
material comprised of viscosifying agents and selected clays.
Barite or other weighting agents may be added to adjust the
specific gravity of the inverter fluid to a value usually slightly
greater than that of the drilling fluid. Selected surface active
agents (surfactants) may be added in sufficient quantity to perform
the tasks of inverting the oil-based fluid and leaving well bore
surfaces in a water-wet condition.
[0056] The process of testing in accordance with the present
invention leads to a determination of a particular inverter fluid
that may be used for inverting the particular test composition of
oleaginous-external/aqueous-internal fluid against which the
inverter fluid is tested. In the particular application of
displacing and inverting a drilling fluid emulsion in an oil or gas
well at the leading end of a stream of a cement composition being
pumped into the well, the inverter fluid to be determined is
typically in the class of fluids referred to as spacers. Such
spacers typically are combined with one or more surfactants to make
up the complete inverter fluid.
[0057] FIGS. 4 and 5 illustrate certain embodiments of the methods
of the present invention, and now will be described. Referring now
to FIG. 4, a flow chart illustrates one embodiment of the methods
of the present invention, generally referred to as method 400.
Method 400 generally comprises determining a composition of an
inverter fluid that may invert, to a desired degree, a test fluid
that comprises an oleaginous-external/aqueous-internal drilling
fluid. In block 402, a potentiometer (e.g., potentiometer 120 of
FIG. 2) may be calibrated. Calibration of potentiometer 120 may be
performed as discussed above. Subsequent to calibration of
potentiometer, fixed-volume testing chamber 102 may be flushed
(e.g., with water) and allowed to dry, as depicted in block 404 of
FIG. 4. Fixed-volume testing chamber 102 may be flushed and dried,
in some embodiments, so that any residue of the inverter fluid
and/or the test fluid may be removed from the surfaces of
electrodes 114, 116.
[0058] In block 406, the test fluid may be preconditioned. Those of
ordinary skill in the art will appreciate that preconditioning of
the test fluid may be performed prior to, simultaneously with, or
subsequent to the steps depicted in blocks 402 and 404.
Preconditioning of the test fluid may be performed as discussed
above. For example, in some embodiments, preconditioning of the
test fluid may comprise utilizing high temperature, high pressure
equipment that is separate from the apparatus of the present
invention. In other embodiments, preconditioning of the test fluid
may occur in fixed-volume testing chamber 102 of an apparatus of
the present invention depicted in FIG. 1. Preconditioning of the
test fluid may occur in fixed-volume testing chamber 102, for
example, to ensure that meter 122/124 reads zero.
[0059] As depicted in block 408, a determination may be made as to
whether preconditioning of the test fluid occurred in fixed-volume
testing chamber 102. If preconditioning of the test fluid did occur
in fixed-volume testing chamber 102, the execution of the method
400 moves to block 414. If preconditioning of test fluid did not
occur in fixed-volume testing chamber 102, the test fluid may be
added to fixed-volume testing chamber 102, as depicted in block
410. Once in fixed-volume testing chamber 102 the temperature and
pressure of fixed-volume testing chamber 102 may be adjusted, as
depicted in block 412, to the temperature and pressure that the
oleaginous-external/aqueous-internal fluid that is being tested
will encounter in the subterranean environment.
[0060] In block 414 of FIG. 4, an initial mixture may be prepared
by injecting a selected inverter fluid into fixed-volume testing
chamber 102 while mixing, until a desired ratio of inverter fluid
to test fluid (e.g., a 50:50 ratio) is obtained. As previously
discussed, the inverter fluid may or may not contain surfactants.
Furthermore, as discussed above, once the desired ratio of the
inverter fluid to the test fluid is obtained, one or more selected
surfactants may be injected into the initial mixture, as depicted
in block 416, until inversion of the test fluid has been detected
based on the measured electrical parameters. Once inversion has
occurred, a composition of a desired inverter fluid may be
determined because the volume and composition of the inverter fluid
in the initial mixture is known, as well as the amount of the one
or more selected surfactants that were injected into the initial
mixture.
[0061] Referring now to FIG. 5, a flow chart illustrates another
embodiment of the methods of the present invention, generally
referred to as method 500. Method 500 generally comprises
determining a composition of an inverter fluid that may invert, to
a desired degree, a test fluid that comprises an
oleaginous-external/aqueous-internal drilling fluid. In block 502,
a potentiometer (e.g., potentiometer 120 of FIG. 2) may be
calibrated. Calibration of potentiometer 120 may be performed as
discussed above. Subsequent to calibration of potentiometer,
fixed-volume testing chamber 102 may be flushed (e.g., with water)
and allowed to dry, as depicted in block 504 of FIG. 5.
Fixed-volume testing chamber 102 may be flushed and dried, in some
embodiments, so that any residue of the inverter fluid and/or the
test fluid may be removed from the surfaces of electrodes 114,
116.
[0062] In block 506, the test fluid may be preconditioned. Those of
ordinary skill in the art will appreciate that preconditioning of
the test fluid may be performed prior to, simultaneously with, or
subsequent to the steps depicted in blocks 502 and 504.
Preconditioning of the test fluid may be performed as discussed
above. For example, in some embodiments, preconditioning of test
fluid may comprise utilizing high temperature, high pressure
equipment that is separate from the apparatus of the present
invention. In other embodiments, preconditioning of the test fluid
may occur in fixed-volume testing chamber 102 of an apparatus of
the present invention depicted in FIG. 1. Preconditioning of the
test fluid may occur in fixed-volume testing chamber 102, for
example, to ensure that meter 122/124 reads zero.
[0063] As depicted in block 508, a determination may be made
whether preconditioning of the test fluid occurred in fixed-volume
testing chamber 102. If preconditioning of the test fluid did occur
in fixed-volume testing chamber 102, the execution of the method
500 moves to block 514. If preconditioning of test fluid did not
occur in fixed-volume testing chamber 102, the test fluid may be
added to fixed-volume testing chamber 102, as depicted in block
510. Once in fixed-volume testing chamber 102 the temperature and
pressure of fixed-volume testing chamber 102 may be adjusted, as
depicted in block 512, to the temperature and pressure that the
oleaginous-external/aqueous-internal fluid that is being tested
will encounter in the subterranean environment.
[0064] In block 514 of FIG. 5, a selected inverter fluid may be
injected into fixed-volume testing chamber 102 while mixing. In
this embodiment, the selected inverter fluid may contain the
desired concentration of the one or more surfactants. As discussed
above, by observation of meter 122/124 during injection of the
selected inverter fluid a desirable ratio of the selected inverter
fluid to the test fluid may be identified, wherein the ratio is
capable of achieving the desired inversion of the
oleaginous-external/aqueous-internal drilling fluid that was used
as the test fluid. In another embodiment, a selected inverter fluid
may be injected into fixed-volume testing chamber 102 to determine
the compatibility of the selected inverter fluid and the test
fluid. The selected inverter fluid may be injected into
fixed-volume testing chamber 102 until a desired ratio of inverter
fluid to test fluid is obtained. Once the desired ratio is
obtained, observation of meter 122/124 will allow determination of
the compatibility of the selected inverter fluid and the test fluid
at the desired ratio. In certain embodiments, the step of adjusting
the temperature and pressure of fixed-volume testing chamber 102 in
block 512 may not occur until the desired ratio of the selected
inverter fluid and the test fluid is obtained by injection of the
selected inverter fluid into fixed-volume testing chamber 102.
[0065] In another exemplary embodiment, as shown in FIG. 6, the
device may be configured to test for fluid compatibility at
elevated temperatures. FIG. 6 illustrates that fixed-volume testing
chamber 102, sample chamber 194, and effluent chamber 196 may be
generally contained within the same instrument case. Sample chamber
194 may be heated by heating element 166. Heating element 146 may
heat fixed-volume testing chamber 102. For example, fixed-volume
testing chamber 102 may be part of a retrofitted consistometer or
viscometer. Apparatus 198 may also have pressure controller 178 to
control the pressure in chamber 200 which in turn may control
pressure in fixed-volume testing chamber 102. Stepper motor 202 may
be used to position actuator 204 to pressurize sample chamber 194
and also transfer a precise portion of fluid into fixed-volume
testing chamber 102 for testing. The user places a first fluid in
fixed-volume testing chamber 102. The user may also place a second
fluid in sample chamber 194, which may be in fluid communication
with fixed-volume testing chamber 102. Both fluids may be any fluid
useful in downhole applications, including but not limited to
drilling fluid and spacer fluid. For example, the first fluid may
be an oil-based mud (OBM), synthetic-based mud (SBM), or any
suitable drilling fluid and the second fluid may be a water-based
spacer fluid containing surfactants as determined applicable via an
Apparent Wettability Test apparatus (SSST device).
[0066] Temperature and pressure measurements may be taken in either
or both chambers (102 and 194). Fixed-volume testing chamber 102
and sample chamber 194 may be heated via heating element to about
the temperature of the subterranean environment where the fluids
will be used. Fixed-volume testing chamber 102 may be pressurized
to about the pressure of the subterranean environment. Sample
chamber 194 may be similarly pressurized. For example, first fluid
may be heated and pressurized according to the appropriate API test
schedule for the depth and temperature gradient the fluids will
experience. For example, temperatures above 190.degree.. In some
embodiments, the temperature may be up to 500.degree. or even
600.degree. or more. Preferably, but not necessarily, the two
chambers may be heated and/or pressurized at the same time.
[0067] Paddle 106 may be stirred at 150 RPM during this
conditioning period. Once final temperature and pressure,
corresponding to a temperature and pressure of about the
temperature and pressure of the subterranean environment are
achieved, the first fluid may be stirred for an additional 20
minutes to fully condition. A first wettability and/or rheology
measurement may be taken in fixed-volume testing chamber 102. A
minimum of three wettability and/or rheology readings may then be
recorded at varying speeds ranging from 2 to 150 RPM. Generally,
the first measured value corresponds with 100% of the first fluid.
Stirring may be reinitiated at 150 RPM. The wettability measurement
may be obtained from contacts inside fixed-volume testing chamber
102 via the two probes at cross-section A-A, as is schematically
illustrated in FIG. 2.
[0068] Stirring may be stopped and 5% by volume of second fluid to
be tested for compatibility may then be injected, forced, or
otherwise moved from sample chamber 194 through stepper motor 202
and actuator 204 into fixed-volume testing chamber 102. This may
displace a portion of the first fluid, causing it to escape from an
opposite side of fixed-volume testing chamber 102. Thus, fluid 100
within fixed-volume testing chamber 102 may become a mixture of
first fluid and second fluid. If second fluid is preheated to
circulating temperature prior to injection, a minimum of three
wettability and/or rheology reading may be recorded for fluid 100
within fixed-volume testing chamber 102 immediately at the same
varying speeds used for the first fluid. If the second fluid was
not preheated, fluid 100 within fixed-volume testing chamber 102
may be stirred for 20-30 minutes prior to taking wettability and/or
rheology readings to allow the temperature to stabilize. The time
will depend on how long it takes fluid 100 within fixed-volume
testing chamber 102 to achieve the designated test temperature and
pressure, corresponding to the temperature and pressure of about
the temperature and pressure of the subterranean environment. Once
the designated temperature and pressure are achieved, a second
wettability and/or rheology measurement may be taken in
fixed-volume testing chamber 102.
[0069] Stirring may be stopped and enough second fluid injected
into fixed-volume testing chamber 102 to yield a final mixture
ratio of 25% second fluid/75% first fluid. The same procedures may
be used regarding temperature conditioning, etc. Once fluid 100
within fixed-volume testing chamber 102 are conditioned, the same
wettability and/or rheology readings may be taken.
[0070] Stirring may again be stopped and enough second fluid
injected into fixed-volume testing chamber 102 to yield a final
mixture ratio of 50% second fluid/50% first fluid. Again, the same
procedures as before may be applied.
[0071] Stirring may again be stopped and enough second fluid
injected into fixed-volume testing chamber 102 to yield a final
mixture ratio of 75% second fluid/25% first fluid. The same
procedures may be followed as in previous steps.
[0072] Stirring may again be stopped and enough second fluid
injected into fixed-volume testing chamber 102 to yield a final
mixture ratio of 95% second fluid/5% first fluid. The same
procedures may be followed as in previous steps.
[0073] Stirring may be stopped once more and enough second fluid
injected to ensure that fixed-volume testing chamber 102 is
completely full of second fluid. This may require a full chamber
volume of displacement. Final wettability and/or rheology readings
may be obtained at the same shear rates as before.
[0074] If it may not be determined that only second fluid remains
in fixed-volume testing chamber 102, it may be desirable to cool
fixed-volume testing chamber 102 and sample chamber 194 and
completely clean them before calibrating and testing is repeated
with the fluids introduced in the opposite order to check some of
the previous measurements. In particular, the measurements for the
50:50 ratio should be the same whether fixed-volume testing chamber
102 initially contains the first fluid or fixed-volume testing
chamber 102 initially contains the second fluid. In addition to
using the methods described for contamination of spacer with mud
when the spacer is used behind a cement slurry. This procedure can
also be used to determine compatibility between the spacer and the
cement.
[0075] FIG. 7 illustrates an embodiment wherein instead of rotating
the paddle with a mag-drive through the lid, the paddle rotates
with a drive below the chamber. Testing may be performed in
substantially the same manner as that used for the embodiments
described with respect to FIG. 6.
[0076] While specific exemplary measurements are disclosed, any
number of other measurements may be taken. For example, a
viscometer may be used to take rheology measurements on any mixture
of first fluid and second fluid. The retrofitted consistometer
described in FIG. 6 may have a variable speed motor controlled with
a feed-back loop. This retrofitted consistometer may be calibrated
to indicate viscosity with a fluid having a known viscosity or
other means that places a predictable torque on paddle 106 attached
to the mag-drive and using the feed-back loop. During a typical
calibration, the inside of the mag-drive is filled with water, air
or a fluid having a known viscosity. Alternatively, as indicated in
FIG. 7, the consistometer may impart a friction if test fluid gets
into the mag-drive area that may or may not be susceptible to
prediction and calibration out of the system. Thus, a more accurate
indication of viscosity may be possible, or other indicators of
whether the slurry thickens or thins may be present.
[0077] Additionally, other types of measurements, including
wettability, may be taken. For example, a potentiometer may be used
to take wettability measurements on any mixture of first fluid and
second fluid. Continual or near-continual measurements may also be
taken. In this instance, the first rheology value may be measured
when fluid 100 within fixed-volume testing chamber 102 have a
percentage of the first fluid and a percentage of the second fluid.
The second rheology value may be measured when fluid 100 within
fixed-volume testing chamber has a smaller percentage of first
fluid and a larger percentage of second fluid. Therefore, any
number of measurements may be taken as the second fluid is
introduced into fixed-volume testing chamber 102. Also, the fluid
that is transferred to effluent chamber 196 can be cooled and
removed from effluent chamber 196 through valves 206 and 208, for
additional tests such as rheology, stability, and visual
observation for wettability.
[0078] This method may be used to take API contamination level
measurements, such that the first Theological measurement are taken
on 100% drilling fluid, 95% drilling fluid and 5% spacer fluid, 75%
drilling fluid and 25% spacer fluid, 50% drilling fluid and 50%
spacer fluid, 25% drilling fluid and 75% spacer fluid, 5% drilling
fluid and 95% spacer fluid, and 100% spacer fluid.
[0079] Therefore, the present invention is well adapted to carry
out the objects and attain the ends and advantages mentioned as
well as those which are inherent therein. While the invention has
been depicted and described by reference to embodiments of the
invention, such a reference does not imply a limitation on the
invention, and no such limitation is to be inferred. The invention
is capable of considerable modification, alternation, and
equivalents in form and function, as will occur to those ordinarily
skilled in the pertinent arts and having the benefit of this
disclosure. The depicted and described embodiments of the invention
are exemplary only, and are not exhaustive of the scope of the
invention. Consequently, the invention is intended to be limited
only by the spirit and scope of the appended claims, giving full
cognizance to equivalents in all respects.
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