U.S. patent application number 12/428454 was filed with the patent office on 2010-10-28 for detecting gas compounds for downhole fluid analysis using microfluidics and reagent with optical signature.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to DAN E. ANGELESCU, CHRISTOPHER HARRISON, JIMMY LAWRENCE, BHAVANI RAGHURAMAN, ROBERT J. SCHROEDER, MATTHEW T. SULLIVAN, RONALD E.G. VAN HAL, TSUTOMU YAMATE.
Application Number | 20100269579 12/428454 |
Document ID | / |
Family ID | 42357773 |
Filed Date | 2010-10-28 |
United States Patent
Application |
20100269579 |
Kind Code |
A1 |
LAWRENCE; JIMMY ; et
al. |
October 28, 2010 |
DETECTING GAS COMPOUNDS FOR DOWNHOLE FLUID ANALYSIS USING
MICROFLUIDICS AND REAGENT WITH OPTICAL SIGNATURE
Abstract
A gas separation and detection tool for performing in situ
analysis of borehole fluid is described. The tool operates by
introducing a reagent to a test sample and causing the resulting
mixture to flow through a microfluidic channel where optical
testing is performed. The optical testing detects a change in a
characteristic of the reagent in response to expose to one or more
particular substances in the test sample. The test sample may be
borehole fluid, a mixture of borehole fluid and scrubbing fluid
subsequently mixed with reagent, a mixture of reagent and gas
separated from borehole fluid, or a mixture of scrubbing fluid and
gas separated from borehole fluid which is subsequently mixed with
reagent. A membrane may be employed to separate one or more target
gasses from the borehole fluid.
Inventors: |
LAWRENCE; JIMMY; (CAMBRIDGE,
MA) ; ANGELESCU; DAN E.; (Noisy le Grand Cedex,
FR) ; HARRISON; CHRISTOPHER; (AUBURNDALE, MA)
; YAMATE; TSUTOMU; (YOKOHAMA-SHI, JP) ; SULLIVAN;
MATTHEW T.; (WESTWOOD, MA) ; SCHROEDER; ROBERT
J.; (NEWTOWN, CT) ; VAN HAL; RONALD E.G.;
(WATERTOWN, MA) ; RAGHURAMAN; BHAVANI; (WILTON,
CT) |
Correspondence
Address: |
SCHLUMBERGER K.K.
2-2-1 FUCHINOBE, CHUO-KU, SAGAMIHARA-SHI
KANAGAWA-KEN
252-0206
JP
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Sugar Land
TX
|
Family ID: |
42357773 |
Appl. No.: |
12/428454 |
Filed: |
April 22, 2009 |
Current U.S.
Class: |
73/152.23 |
Current CPC
Class: |
G01N 33/2823 20130101;
E21B 47/113 20200501 |
Class at
Publication: |
73/152.23 |
International
Class: |
E21B 49/08 20060101
E21B049/08 |
Claims
1. Apparatus for detecting a substance of interest in a borehole
fluid in a borehole comprising: a first port through which a test
sample fluid is introduced; a second port through which a reagent
is introduced to the test sample fluid, thereby creating a mixed
fluid, the mixed fluid exhibiting a characteristic change if the
substance of interest is present in the borehole fluid; a
microfluidic device into which the mixed fluid is introduced; a
test module that detects, within the borehole, the characteristic
change in the mixed fluid in the microfluidic channel; and a
transmitter that outputs a signal indicative of whether the
characteristic change is detected.
2. The apparatus of claim 1 further including a component
separator.
3. The apparatus of claim 1 further including a pressure
compensator to balance fluid pressure inside and outside the
apparatus
4. The apparatus of claim 1 further including a fluid delivery
module to introduce each respective fluid.
5. The apparatus of claim 1 wherein the signal outputted by the
transmitter is indicative of level of concentration of the
substance of interest in the borehole fluid.
6. The apparatus of claim 1 wherein the test module includes an
optical transmitter and optical receiver that detect differences in
color or transmissivity.
7. The apparatus of claim 1 wherein the reagent is selected from
the group consisting of fluorescein mercuric acetate, complexes of
metal cation and organic compounds and organometallic materials,
combined with various appropriate solvents, and combinations
thereof, suitable for both ambient and borehole condition use.
8. The apparatus of claim 1 wherein the test sample fluid is
borehole fluid.
9. The apparatus of claim 1 wherein the test sample fluid is
borehole fluid mixed with scrubbing fluid
10. The apparatus of claim 1 wherein the microfluidic device
includes an integrated mixer.
11. The apparatus of claim 1 wherein a target compound for analysis
can be transferred from one phase at feed side to another phase at
permeate side.
12. The apparatus of claim 1 wherein the microfluidic device and
test module are integrated as one device.
13. The apparatus of claim 1 further including a membrane disposed
between the borehole fluid and the first port, and wherein the test
sample fluid is a fluid separated from the borehole fluid by the
membrane.
14. The apparatus of claim 13 wherein the membrane includes
capillary tubing.
15. The apparatus of claim 13 wherein the membrane capillary tubing
is supported by a structure that increases diffusion area.
16. The apparatus of claim 14 wherein the capillary tubing is
wound.
17. The apparatus of claim 14 wherein the membrane includes a thin
film, multilayered micro porous or nano porous membrane
18. The apparatus of claim 1 wherein the test sample fluid is a
mixture of scrubbing fluid and borehole fluid.
19. The apparatus of claim 1 further including a membrane disposed
between the borehole fluid and the first port, and wherein the test
sample fluid is a mixture of scrubbing fluid and gas separated from
the borehole fluid by the membrane.
20. The apparatus of claim 1 wherein the first and second ports are
part of a multi-port valve, and wherein a test loop is connected
between ports of the valve in order to introduce a predetermined
fixed volume of reagent.
21. The apparatus of claim 1 adapted to operate in a borehole.
22. The apparatus of claim 1 further including a piston for
delivering at least one of the fluids in response to pumped
pressure from another one of the fluids.
23. The apparatus of claim 1 further including a piston for
delivering at least one of the fluids in response to borehole
pressure.
24. The apparatus of claim 1 wherein the apparatus is pressure
balanced with at least one of: a spring and piston, bellows, and
diaphragm membrane.
25. The apparatus of claim 1 further including a combined passive
mixer and membrane module.
26. The apparatus of claim 1 further including thin wall capillary
tubing which functions as an optical waveguide, the tubing coupled
to an optical source and detector.
27. The apparatus of claim 1 wherein multiple sample loops are
disposed between the ports on a single chip.
28. The apparatus of claim 27 wherein the sample loops are operated
by at least one of: multiposition switching valves; and one time
use valves.
29. A method for detecting a substance of interest in a borehole
fluid comprising: introducing a test sample fluid via a first port;
introducing a reagent to the test sample fluid via a second port,
thereby creating a mixed fluid, the mixed fluid exhibiting a
characteristic change if the substance of interest is present in
the borehole fluid; causing at least some of the mixed fluid to
flow into a microfluidic device; detecting, within the borehole,
the characteristic change in the mixed fluid in the microfluidic
channel with a test module; and transmitting an output signal
indicative of whether the characteristic change is detected.
30. The method of claim 29 further including transmitting an output
signal indicative of level of concentration of the substance of
interest in the borehole fluid.
31. The method of claim 29 wherein the test module includes an
optical transmitter and optical receiver, and further including
detecting differences in color or transmissivity.
32. The method of claim 29 wherein introducing the test sample
fluid includes introducing borehole fluid.
33. The method of claim 29 further including a membrane disposed
between the borehole fluid and the first port, and wherein
introducing the test sample fluid includes introducing a gas
separated from the borehole fluid by the membrane.
34. The method of claim 29 wherein introducing the test sample
fluid includes introducing a mixture of scrubbing fluid and
borehole fluid.
35. The method of claim 29 further including a membrane disposed
between the borehole fluid and the first port, and wherein
introducing the test sample fluid includes introducing a mixture of
scrubbing fluid and gas separated from the borehole fluid by the
membrane.
36. The method of claim 29 wherein the first and second ports are
part of a multi-port valve, and wherein a test loop is connected
between ports of the valve, and wherein introducing reagent
includes causing a predetermined fixed volume of reagent to flow
into the test loop.
Description
FIELD OF THE INVENTION
[0001] The invention is generally related to analysis of borehole
fluid, and more particularly to in situ detection of gaseous
compounds in a borehole fluid using a reagent which exhibits an
optical signature in a microfluidic channel in response to exposure
to certain substances.
BACKGROUND OF THE INVENTION
[0002] Phase behavior and chemical composition of borehole fluids
are known to be useful information. For example, concentration of
gaseous components such as carbon dioxide, hydrogen sulfide and
methane in borehole fluid are indicators of the economic viability
of a hydrocarbon reservoir. Concentrations of CO.sub.2 and H.sub.2S
are of interest because CO.sub.2 corrosion and H.sub.2S stress
cracking caused by relatively high concentrations are leading
causes of mechanical failure of production equipment. CH.sub.4
concentration is of interest as an indicator of the calorific value
of gas wells. It is therefore desirable to be able to perform fluid
analysis quickly, accurately, reliably, and at low cost.
[0003] A variety of techniques and equipment are available for
performing fluid analysis in a laboratory. However, retrieving
samples for laboratory analysis is time consuming and prone to
error. Due to the difference in environmental conditions between a
location in a borehole and a location at the surface, and other
factors, some of the characteristics of borehole fluids change when
the fluids are brought to the surface. For example, because
hydrogen sulfide gas readily forms non-volatile and insoluble metal
sulfides by reaction with many metals and metal oxides, analysis of
a fluid sample retrieved with a metallic container can produce an
inaccurate estimate of sulfide content. This presents a
technological problem because fluid analysis techniques that are
known for use at the surface are generally impractical in the
borehole environment due to size limitations, extreme temperature,
extreme pressure, presence of water, and other factors. Another
technological problem is isolation of gases, and particular species
of gas, from the borehole fluid, which commonly exist as multiphase
fluids in borehole.
[0004] The technological problems associated with detection of gas
in fluids have been studied in this and other fields of research.
For example, US20040045350A1, US20030206026A1, US20020121370A1,
GB2415047A, GB2363809A, GB2359631A, U.S. Pat. No. 6,995,360B2, U.S.
Pat. No. 6,939,717B2, WO2005066618A1, WO2005017514A1,
WO2005121779A1, US20050269499A1, and US20030134426A1 describe an
electrochemical method for H2S detection using membrane separation.
US20040045350A1, GB2415047A, and GB2371621A describe detecting gas
compounds by combining infrared spectrophotometry and a membrane
separation process. US20060008913 AI describes the use of a
perfluoro-based polymer for oil-water separation in microfluidic
system. US2006000382A1 describes a microfluidic system for downhole
chemical analysis which samples a portion of water based sample
fluid and mixes it with pH sensitive reagent for low temperature pH
measurement applications. Toda et al. (Lab Chip, 2005, 5,
1374-1379) describes a system to measure H2S concentration using a
calorimetric technique and honeycomb structured microchannel
scrubbers. However, the system and the reagent described are not
suitable for use in a downhole environment such as that encountered
in oilfield operations. U.S. Pat. No. 6,925,392B2 describes a
microfluidic device which reacts to specific characteristics of a
fluid during operations. The device is recovered and subjected to
analysis to measure the desired characteristics such as
resistivity, chloride, calcium concentration and other fluid
properties. However, a real-time microfluidic-based sensing system
capable of operation over a wide temperature and pressure range and
in harsh conditions such as those encountered in oilfield
operations has not yet been developed.
SUMMARY OF THE INVENTION
[0005] In accordance with an embodiment of the invention, apparatus
for detecting a substance of interest in a borehole fluid in a
borehole comprises: a first port through which a test sample fluid
is introduced; a second port through which a reagent is introduced
to the test sample fluid, thereby creating a mixed fluid, the mixed
fluid exhibiting a characteristic change if the substance of
interest is present in the borehole fluid; a microfluidic device
into which the mixed fluid is introduced; a test module that
detects, within the borehole, the characteristic change in the
mixed fluid in the microfluidic channel; and a transmitter that
outputs a signal indicative of whether the characteristic change is
detected.
[0006] In accordance with another embodiment of the invention, a
method for detecting a substance of interest in a borehole fluid
comprises: introducing a test sample fluid via a first port;
introducing a reagent to the test sample fluid via a second port,
thereby creating a mixed fluid, the mixed fluid exhibiting a
characteristic change if the substance of interest is present in
the borehole fluid; causing at least some of the mixed fluid to
flow into a microfluidic device; detecting, within the borehole,
the characteristic change in the mixed fluid in the microfluidic
channel with a test module; and transmitting an output signal
indicative of whether the characteristic change is detected.
[0007] One of the advantages of the invention is that borehole
fluid can be analyzed in situ. In particular, the reagent is
introduced to the test sample fluid and the mixture is tested
within the borehole. Consequently, time consuming fluid retrieval
and errors caused by changes to fluid samples due to changes in
conditions between the borehole and the environment are at least
mitigated.
[0008] The use of microfluidic technology helps to achieve some of
the advantages of the invention. Generally, microfluidics is a
technique for processing and manipulating volumes of fluid on the
order of nanoliters in a micrometer scaled channel known as a
microchannel. As a result, fluid flow is laminar within the
microchannel. A static or active mixer module may therefore used to
enhance mixing of fluids and achieving a mixing ratio value of the
mixed fluids. Microfluidics is distinct because manipulation of
microliters of fluid in a laminar flow regime offers fundamentally
new capabilities in the control of concentrations of molecules in
space and time, the result of which facilitates detection of
physical properties. It will therefore be appreciated that
microfluidic technology offers advantages for analytical
applications including small footprint, small sample and reagent
volumes, the ability to carry out various processes such as
separation and detection with high resolution and sensitivity, and
low cost and reduced analysis time.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 illustrates a logging tool for gas separation and
detection in a borehole.
[0010] FIG. 2 illustrates introduction of reagent fluid and optical
testing in the microfluidic channel in greater detail.
[0011] FIG. 3 illustrates an embodiment in which borehole fluid is
mixed directly with reagent fluid prior to testing.
[0012] FIGS. 4a through 4c illustrate mechanisms to deliver test
sample fluid and reagent into the microfluidic device,
[0013] FIGS. 5a through 5c illustrate integration of the mixing and
optics functions into the microfluidic channel.
[0014] FIG. 6 illustrates alternative embodiments of the
microfluidic optics. FIG. 7 illustrates an embodiment in which
scrubbing fluid is mixed with borehole fluid to create an
intermediate fluid which is subsequently mixed with reagent fluid
prior to testing.
[0015] FIG. 8 illustrates an embodiment in which gas is separated
from the borehole fluid using a membrane, and the reagent fluid is
mixed with the separated gas prior to testing.
[0016] FIG. 9 illustrates an embodiment in which gas is separated
from the borehole fluid using a membrane, the scrubbing fluid is
mixed with the separated gas, and reagent fluid is subsequently
mixed with the scrubbing fluid/gas mixture prior to testing.
[0017] FIGS. 10 and 11 illustrate the use of a thin capillary
membrane.
[0018] FIGS. 12 and 13 illustrate an embodiment in which a 6-port
valve and sample loop are used to introduce fluids prior to
measurement.
[0019] FIGS. 14a through 14d illustrate an alternative to the 6
port valve-based system of FIGS. 12 and 13.
[0020] FIG. 14 illustrates a method in accordance with the
invention.
[0021] FIG. 15 illustrates a capillary tubing support
structure.
[0022] FIG. 16 illustrates an experimental flow injection analysis
of dissolved sulfide in water.
[0023] FIG. 17 illustrates an experimental result of H2S gas
measurement using a thin wall capillary tubing membrane based
microfluidic device.
DETAILED DESCRIPTION
[0024] Referring to FIG. 1, a tool string 100 is utilized to
measure characteristics of fluid in a borehole 102. The borehole
may be formed through a hydrocarbon reservoir 106 adjacent to an
impermeable layer 108, and various other layers which make up the
overburden 110. The tool string, which may be part of a wireline
logging tool string, logging-while-drilling tool string, or other
device, is operable in response to a control unit 104 which may be
disposed at the surface. The control unit 104 may also be capable
of data analysis. The tool string 100 is connected to the control
unit 104 by a logging cable for a wireline tool, or by a drill pipe
string for a LWD tool. The tool string 100 includes a gas detection
tool 112 which is lowered into the borehole to measure physical
properties associated with fluid in the borehole or formation. Data
gathered by the tool 112 may be communicated to the control unit in
real time via the wireline cable or LWD telemetry.
[0025] FIG. 2 illustrates basic principles of operation of the gas
detection tool 112 (FIG. 1). A reagent 200 is exposed to a test
sample fluid 202 to produce a mixed fluid 204. Within the mixed
fluid 204, the reagent 200, test sample fluid 202, or both, exhibit
a change in at least one physical characteristic due to presence of
one or more specific substances or classes of substances in the
test sample fluid. For example, and without limitation, the reagent
may exhibit a change in color if a substance such as CO2, or H2S,
or CH4 from the test sample fluid is present in the mixed fluid.
Further, the degree of characteristic change may be a function of
concentration of the substance, exposure time, or both. The mixed
fluid 204 is then caused to flow through a microfluidic device 206,
where the mixed fluid is subjected to testing. The testing may be
performed by an optical testing module designed to detect a change
in color or transmissivity exhibited by the reagent. The optical
module may include a low dead volume optical flow cell or a
microfluidic optical flow cell. In one embodiment the optical
testing module includes an optical transmitter 208 such as a UV-Vis
source and optical receiver 210 such as a CCD spectrometer which
detects changes in color or optical absorbance. The testing module
produces an output signal which is indicative of the detected
changes. Further, the output signal may be indicative of the degree
of change. The output signal is provided to interpretation
circuitry and software in control unit 104, which processes the
output signal to characterize the test sample fluid, e.g., in terms
of whether a certain gas or reaction products of a certain gas and
reactants has been detected. Further processing may provide an
indication of the concentration of that gas in the borehole fluid.
It will be appreciated that the processing software will include a
computer program product stored on a computer readable medium. As
will be explained below, the test sample fluid can include various
different fluids, either alone or in combination.
[0026] The reagent 200 is selected based on which gas or gasses the
operator wishes to detect and measure. For example, the reagent may
be selected based on ability to react with or absorb the gas or
gasses of interest at a predictable rate or extent as a function of
gas concentration in the borehole fluid. Further, the response of
the reagent to exposure to the gas or gasses of interest should
cause a characteristic change in the reagent, gas, or other
substance that can be detected, and possibly measured. Examples of
reagents that may be used to detect hydrogen sulfide gas include,
but are not limited to, fluorescein mercuric acetate, complexes of
metal cation and organic compounds and organometallic materials,
combined with various appropriate solvents.
[0027] The microfluidic device 206 is defined by a rigid housing
which permits light from the test module to traverse the channel
from the optical transmitter to the optical receiver. The device
206 is characterized by channel diameter of around 100 nanometers
to several hundred micrometers and, in the case of a rectangular
channel, at least one of its internal dimension is less than
several hundred micrometers. The flow of fluid within the
microfluidic device is characterized by the Reynolds number,
Re = LV avg .rho. .mu. ##EQU00001##
where L is the most relevant length scale, .mu. is the viscosity, r
is the fluid density, and V.sub.avg is the average velocity of the
flow. L may be 4A/P, where A is the cross sectional area of the
device and P is the wetted perimeter of the channel. Re is on the
order of unity for typical microfluidic applications, and a laminar
flow is expected for Newtonian fluids and fluids with negligible
elasticity. In this invention Re can be up to 5, e.g., a range of
0.01 to 50 microliter/min (50 for low viscosity fluids). Because of
the dimensions of the microfluidic device and the properties of the
reactive fluid, the flow of the reactive fluid through the device
is laminar, i.e., without turbulence.
[0028] FIG. 3 is a block diagram of an embodiment of the gas
detection tool 112 (FIG. 1) in which the reagent 200 is mixed
directly with borehole fluid 300. This embodiment includes at least
two input ports 302, 304. One input port 302 is employed for
receiving borehole fluid 300 and another input port 304 is employed
for receiving the reagent 200, e.g., from a reservoir. The borehole
fluid and reagent are mixed in a static mixer 306, thereby creating
the mixed fluid, e.g., a metal sulfide in solution. The mixed fluid
is then caused to flow through the microfluidic device 206, wherein
the mixed fluid is subjected to optical testing. The tested fluid
is then ejected as waste.
[0029] Various means are known for inducing fluid flow. While the
particular fluid flow technique is not critical to the invention,
some alternatives will be described for completeness. Generally,
fluid may be caused to flow through the microfluidic device 206 by
differential pressure or electrokinetic means. A positive
displacement pump may be employed in order to implement pressure
driven flow. Electrodes may be employed to implement electrokinetic
driven flow. Electrokinetic driven flow is enabled by an electric
surface charge including a double layer of counter ions which forms
on the channel housing surface. When an electric field is applied
across the microfluidic channel using the electrodes, the ions in
the double layer move toward the electrode of opposite polarity.
This causes motion of the reactive fluid near the walls of the
housing, which is transferred via viscous forces into convective
motion of the fluid. Other means of inducing fluid flow including
but not limited to piezoelectric based micro pumps and impeller
based pumps might alternatively be employed.
[0030] FIGS. 4a through 4c illustrate mechanisms to deliver test
sample fluid and reagent into the microfluidic device. Generally,
fluid flow is induced by pump, the use of borehole pressure with a
fluid restrictor to regulate fluidic flows, or some combination of
the techniques. FIG. 4a specifically illustrates use of independent
pumps 401, 403 for the causing the test sample fluid 202 and
reagent 200, respectively, to flow into the microfluidic device
206. FIG. 4b illustrates a variant in which a single pump 405
causes test sample fluid 202 to flow to a tee 407. From the tee 407
the fluid 202 flows in two paths: a first path into the
microfluidic device 206; and a second path to a piston cylinder
409. The flow of fluid 202 into the piston cylinder 409 actuates
the piston cylinder, thereby causing reagent to flow into the
microfluidic device 206. A fluid restrictor 411 may be used to
control the pressure and volume of reagent introduced to the
microfluidic device. FIG. 4c illustrates a variant in which
borehole pressure is used to cause test sample fluid 202 to flow to
the tee 407. Borehole pressure thereby actuates the piston cylinder
to introduce reagent into the microfluidic device 206. A second
fluid restrictor 413 is used to control the volume and pressure of
test sample fluid 202 introduced to the microfluidic device
206.
[0031] The various pumps described above can be, without
limitation, conventional reciprocating, piezoelectric, impeller
based pumps, controllable by mechanical connections or magnetic
actuation, preferably small enough to suit the size and flow rate
required from microfluidic device. Some examples are described in
Laser et al. 2004 J. Micromech. Microeng. 14 R35-R64; C. Yamahata,
M. Chastellain, V. K. Parashar, A. Petri, H. Hofmann, and M. A. M.
Gijs, "Plastic Micropump With Ferrofluidic Actuation," J.
Microelectromechanical Systems 14 (1), 2005; and Lei et al.
PROCEEDINGS-INSTITUTION OF MECHANICAL ENGINEERS PART H JOURNAL OF
ENGINEERING IN MEDICINE 2007, VOL 221; NUMB 2, pages 129-142.
[0032] In addition to controlling flow of the fluid to execute
multiple tests, fluid flow may be varied in order to facilitate
testing over a greater range of gas concentrations. Because the
volume of reagent fluid exposed to separated gas is relatively
small, the reagent fluid may become saturated if fluid flow rate is
relatively slow between mixing and testing, gas concentration is
relatively high, or both. In order to avoid saturation, and thereby
facilitate measurement over a greater range of concentrations, the
rate of fluid flow may be varied such that both exposure time and
gas concentration as indicated by optical signature are provided as
data to the control unit. It will be appreciated that slowing the
rate of reagent fluid flow may enhance detection of separated gas
at relatively low concentrations, whereas increasing the rather of
reagent fluid flow may enhance detection of separated gas at
relatively high concentrations.
[0033] FIGS. 5a through 5c illustrate some features of the tool
implemented on a chip 555. The mixing function can be important
because mixing characteristics differ between laminar flows and
non-laminar flows. Typically, microfluidic flows have a high Peclet
number, e.g., Pe=U.l/D, where U=average flow velocity l=channel
dimension and D=molecular diffusivity. The diffusive mixing time is
given by tD.about.l 2/D. Therefore, the mixing channel length
required to achieve an adequate species mixing increases linearly
with the Peclet number (Lm.about.Pe.times.1). For example, an
average flow velocity of 500 micrometer/s, a channel dimension of
100 micrometer and a molecular diffusivity of 10 .mu.m2/s will
require a mixing time and channel length in the order of 1000 see
and 0.5 m, respectively. Variations of the mixer 306 (FIG. 3) are
shown in FIG. 5a. In most cases, a microfluidic device with a
passive mixer structure such as a staggered herring bone structure
501, wherein a series of ridges are employed to induce helical flow
and improve mixing efficiency (See Strook et al, Science, 295,
647-651 (2002) for a discussion of the underlying principles). The
mixing function can also be accomplished with a serpentine
structure 503 including a series of turns which induce mixing due
to differences in distance travelled by the fluid as direction
changes, i.e., faster flow at the outside of the corner than at the
inside of the corner. Alternatively, a micropump such as an
impeller based pump can function as a mixer. As illustrated
specifically in FIG. 5b, optical fibres 505, 507 may be mated to
the microfluidic device such that light traverses a segment of the
microfluidic device 206. For example, the fibres may be abutted
against the channel where the channel is at a right angle. Thus,
light from one fibre 505 enters and traverses the channel, and
exits via another fibre 507. A variation which incorporates the
mixing function into the microfluidic device, e.g., onto a single
chip with the optical detection module, is illustrated specifically
in FIG. 5c. More particularly, the mixing feature and microfluidic
optics are both be disposed on the chip such that the mixing
function occurs upstream of the microfluidic optics.
[0034] Variations of the microfluidic optics are illustrated in
FIGS. 6a and 6b. As shown in FIG. 6a, the microfluidic device may
function as an optical waveguide such that a non-linear optical
test segment 611 is possible. In this variant the channel which
contains the fluid has a reflective inner coating with a suitable
refractive index such that incident light does not escape. Light is
introduced to the non-linear test segment 611 via optical fibres
505, 507 as already discussed above. One advantage of this
embodiment is that the length of the optical test section can be
increased beyond the basic length and width of the chip 555. As
shown in FIG. 6b, the test segment may alternatively be formed by
having the light traverse the microfluidic channel at right angles.
In other words, the light path of the test segment 613 is linear
and perpendicular to the fluid flow path. Background technology is
described in Monat et al, Nature Nanophotonics, 1, 2007, 106
[0035] FIG. 7 is a schematic/block diagram illustrating that
multiple mixers 502, 504 may be implemented with microfluidic
device 206 optics on a single chip 555. It will also be appreciated
that multiple independent test modules (microfluidic optics with or
without other components, a.k.a., sample loops) may be implemented
on a single chip. For example, an array including multiple one-time
use test modules could be implemented with one-time use valves 777
for introducing the fluids such that the chip could be discarded
after all modules were used. Alternatively, multiple reusable test
modules could be implemented on the chip. One advantage of
implementing an array of test modules is that characteristic such
as fluid volumes and the length of optical test segment could
differ between test modules, thereby supporting operation in a
broader range of conditions and for a broader range of borehole
fluids.
[0036] As suggested above, it may be undesirable to directly mix
reagent with borehole fluid. One technique to avoid such a direct
mixture is to use a scrubbing fluid 500 to create an intermediate
fluid from the borehole fluid 300. The scrubbing fluid is selected
to neutralize characteristics of the borehole fluid which make it
unsuitable for direct mixture with reagent. The scrubbing fluid may
also improve gas solubility, which is advantageous if gas
solubility into the reagent is low. For example in the case of
acidic gas, alkaline solution such as sodium hydroxide, alkanoamine
compounds such as triethanolamine, diethanolamine, and
methyldiethanolamine may be used. Organic solvents such as DMF and
NMP, glycol based compounds (ethylene glycol, propylene glycol,
diethylene glycol monobutyl ether) can also be used as
stripping/scrubbing fluid. In practice, the scrubbing fluid and
borehole fluid may be introduced to a static mixer 502 to create
the test sample fluid. The test sample fluid and reagent 200 are
then introduced to a second static mixer 504 to create the mixed
fluid which undergoes testing in the microfluidic device 206. As
discussed above, the mixers and microfluidic device optics may be
implemented on one chip as a single or multiple test module
configuration.
[0037] FIG. 8 is a block diagram of an alternative embodiment of
the gas detection tool 112 (FIG. 1) in which the test sample fluid
is a gas 400 that is separated from the borehole fluid 300 by a gas
separation membrane 402. Borehole fluid 300 flows though a channel
404 on one side of the membrane, and reagent fluid 200 from a
reservoir 406 flows through a channel 408 on the opposite side of
the membrane 402. Openings associated with the channel 404 carrying
borehole fluid may be open to the borehole in a manner which takes
advantage of fluid flow within the borehole to refresh the fluid
within the channel 404. The channel 408 carrying reagent is
connected to the reagent reservoir 406 at one opening and to a
static mixer 306 at another opening. Fluid that is mixed by the
mixer flows into the microfluidic channel 206. If present, one or
more particular types of gas 400 are separated from the borehole
fluid 300 by the membrane 402. The reagent 200 mixes with separated
gas in the static mixer 306 at the end of channel 408. The reagent
200 exhibits a change in a physical characteristic in response to
exposure to the separated gas in the gas/reagent mixture. The
change is then detected via optical testing in the microfluidic
channel 206 as already described above. An advantage of this
variant is that the reagent is not directly exposed to borehole
fluid. Depending on the composition of the borehole fluid and the
reagent, such separation may be desirable. For example, the
borehole fluid may be so dark in color that it would induce errors
in the optical testing.
[0038] The membrane 402 has characteristics that inhibit traversal
by all but one or more selected compounds. Various commercially
available gas separation membranes might be utilized. Such
membranes are typically available as either a thin film or a thin
wall tubing, either of which might be used for membrane 402. The
membrane may be constructed of any of various materials, ones of
which may be preferable based on downhole conditions and the
substance one wishes to detect. One embodiment of the membrane is
an inorganic, gas-selective, molecular separation membrane having
alumina as its base structure, e.g., a DDR type zeolite membrane.
Another embodiment is a polymeric membrane, such as a highly
thermally stable polymeric membrane such as Teflon AF (DuPont),
PDMS or microporous PTFE (Gore-Tex). In a polymeric membrane such
as Teflon AF or PDMS, gas molecules permeate through the membrane
via a solution-diffusion process, whereas in an inorganic or
microporous membrane the gas permeates through Knudsen diffusion.
In the case of a zeolite membrane, nanoporous zeolite material is
grown on the top of a base material. Examples of such membranes are
described in US20050229779A1, US6953493B2 and US20040173094AI. The
membrane may be characterized by a pore size of about 0.3-0.7
.mu.m, resulting in a strong affinity towards CO2. Further
enhancement of separation and selectivity characteristics of the
membrane can be accomplished by modifying the surface structure.
For example, a water-impermeable layer such as a perfluoro-based
polymer may be applied to inhibit water permeation through the
membrane. Other variations of the separation membrane operate as
either molecular sieves or adsorption-phase separation. These
variations can formed of inorganic compounds, inorganic sol-gel,
inorganic-organic hybrid compounds, inorganic base material with
organic base compound impregnated inside the matrix, and any
organic materials that satisfy requirements.
[0039] FIG. 9 is a block diagram of an alternative embodiment of
the gas detection tool 112 (FIG. 1) in which the test sample fluid
is formed by mixing scrubbing fluid 500 with a gas 400 that is
separated from the borehole fluid 300 by a gas separation membrane
402. Borehole fluid 300 flows though a channel 404 on one side of
the membrane 402, and scrubbing fluid 500 flows from a reservoir
600 through a channel 408 on the opposite side of the membrane. The
channel 408 carrying scrubbing fluid 500 is connected to a
scrubbing fluid reservoir 600 at one opening and to a static mixer
602 at another opening. If present, one or more particular types of
gas 400 are separated from the borehole fluid by the membrane 402.
The scrubbing fluid mixes with separated gas in the mixer 602,
thereby creating a test sample fluid. The test sample fluid is then
mixed with reagent 200 in a second static mixer 604. The reagent
exhibits a change in a physical characteristic in response to
exposure to gas in the test sample fluid. The change is then
detected via optical testing in the microfluidic channel 206 as
already described above.
[0040] FIGS. 10 and 11 illustrate the use of a thin capillary
membrane 902 to selectively allow permeation of gas from the
borehole fluid 300. The capillary membrane allows very high surface
to volume ratio, and is less prone to leaking from channel to
channel in comparison with a thin film membrane with a planar
fluidic channel. For example, the tubing can be rolled into a
compact form factor, and the necessary reagent retention time can
be adjusted by adjusting tubing length or flow rate. With a thin
film membrane, only flow rate can be adjusted. Further, it is
relatively difficult to produce large membrane sheets. Scrubbing
fluid can be employed to assist the reaction as already described
above. Flowing fluid with stop-go method will also assist the
detection.
[0041] Flow injection analysis, proposed by Ruzicka et al in 1974,
is a reliable and reproducible method to conduct chemical analysis.
A portion of the sample is introduced into a flowing stream of
reagent and property changes are detected afterwards. The method's
accuracy can be improved using a switching valve equipped with a
sample loop.
[0042] FIGS. 12 and 13 illustrate a specific implementation of the
gas detection tool 112 (FIG. 1) in which a 6-port valve 700 is used
to introduce test sample fluids to a sample loop 702 prior to
testing. The valve 700 has six ports, 1-6. Port 1 is used to
introduce test sample fluid 202 continuously. Port 4 is used to
introduce reagent 200. The valve is characterized by two distinct
configurations between which the valve can be switched. In a first
configuration (shown specifically in FIG. 10) port 1 is connected
to port 6, port 2 is connected to port 3, and port 4 is connected
to port 5. In this first configuration the test sample fluid 202
flows into port 1, to port 6, into a sample loop 702 between ports
6 and 3, and from port 3 to port 2, which is connected to a waste
fluid conduit or recycling reservoir. The volume of the channel
between port 1 and port 2 is known. Consequently, the volume of
sample fluid in the channel, and in particular the volume of test
sample fluid in the sample loop 702, is fixed and known. The
reagent 200 flows continuously from port 4 to 5 and into the mixer
and optical module. Baseline measurement can be conducted in this
configuration. The valve 700 is then switched to a second
configuration (shown specifically in FIG. 13). In the second
configuration port 3 and 4 are connected, causing the reagent 200
to flow to the sample loop 700 via port. The test sample fluid and
reagent are then mixed, moved through the sample loop and out of
port 5 to the static mixer 704 and microfluidic channel 206 for
optical testing. One of the advantages of the implementation is
enhanced control over the volume of reagent introduced for each
test cycle. Under specific circumstances the inlet of reagent 200
and test sample fluid 202 can be reversed.
[0043] FIGS. 14a through 14d illustrate an alternative to the 6
port valve-based system. This alternative embodiment includes two
plunger-like piston valves 1200 made of a ferrous component coated
with an inert, low friction, slightly elastic substance on the
surface for better sealing. These valves 1200 can be actuated with
magnetic components 1202. When the left side magnets are activated,
the baseline signal of the reagent is measured. When the right side
magnets are activated, the pistons slide and sample fluid enters
the sample loop (middle channel). When the left side magnets are
activated again, the pistons slide to the left again, and reagent
swipes the "trapped" sample to the mixer and detector. Piston
movements are adjusted by balancing pressures of these fluids and
also to use pressure difference between these fluids to improve
sealing.
[0044] Referring to FIG. 15, it will be appreciated that the
invention can also be expressed in terms of a method. Initially, a
sample of borehole fluid is obtained and a known volume of reagent
is prepared, as indicated in steps 800, 802, respectively.
Optionally, a scrubbing fluid may be prepared as indicated by step
804. Note that "prepared" implies that the fluid can be introduced
at a known volume or rate of flow, and does not imply a
manufacturing process. Any of various alternative techniques can
then be employed to produce a test sample fluid. In one technique
the known volume of reagent and borehole fluid sample are combined
in step 806. In another technique a gas is separated from the
borehole fluid in step 808, and the separated gas is combined with
the reagent in step 810. In another technique a gas is separated
from the borehole fluid in step 808, and the separated gas is
combined with the scrubbing fluid in step 812, and the resulting
fluid is combined with reagent in step 814. In another alternative
embodiment the borehole fluid is combined with scrubbing fluid in
step 816, and the resulting fluid is combined with reagent in step
818. Since any of the techniques might be employed, the results are
depicted as proceeding to a logical OR step 820. The test sample
fluid is then subjected to optical testing in step 822. A signal
indicative of the result of the test is then transmitted to
processing circuitry as indicated by step 824.
[0045] FIG. 15 illustrates a capillary tubing support structure. As
discussed above, a thin capillary tubing membrane 902 can be used
to selectively allow permeation of gas from the borehole fluid. The
capillary membrane is advantageously characterized by a high
surface to volume ratio, and is less prone to leaking from channel
to channel in comparison with a thin film membrane with a planar
fluidic channel. As illustrated, the tubing can be rolled into a
compact form factor. In particular, the tubing membrane is wrapped
around a support structure which occupies less than several percent
of the entire surface area.
[0046] FIG. 16 illustrates an experimental flow injection analysis
of dissolved sulfide in water. The experiment was conducted at 150
deg C., 5200 psi, using a 5 .mu.l (microliter) sample loop. The
sample fluid was injected into a flowing stream of reagent, and the
color change/optical signature was detected using a microfluidic
optical cell with a pathlength of 10 mm. The optical signature can
be observed at 400 nm. Using 850 nm (or higher) as a
baseline/reference, the difference between these two signals can be
used to quantify the sulfide.
[0047] FIG. 17 illustrates an experimental result of H2S gas
measurement using a thin wall capillary tubing membrane based
microfluidic device. The gas permeable capillary tubing was wrapped
into a mechanical support. Reagent was then flowed into the
capillary tubing, e.g., at 50 .mu.l/min, and H2S gas was flowed at
the feed side, i.e., outside of the capillary tubing. The reaction
product was detected using a microfluidic optical cell with a test
segment pathlength of 10 mm. The signal was acquired at 400 nm and
used "as is." Baseline correction, for example at 800 nm, could be
used to improve accuracy.
[0048] While the invention is described through the above exemplary
embodiments, it will be understood by those of ordinary skill in
the art that modification to and variation of the illustrated
embodiments may be made without departing from the inventive
concepts herein disclosed. Moreover, while the preferred
embodiments are described in connection with various illustrative
structures, one skilled in the art will recognize that the system
may be embodied using a variety of specific structures.
Accordingly, the invention should not be viewed as limited except
by the scope and spirit of the appended claims.
* * * * *