U.S. patent application number 12/138756 was filed with the patent office on 2008-10-23 for spectroscopic ph measurement at high-temperature and/or high-pressure.
This patent application is currently assigned to Schlumberger Technology Corporation. Invention is credited to Craig Borman, Jinglin Gao, Gale Gustavson, Moin Muhammad, Philip Rabbito, Bhavani Raghuraman.
Application Number | 20080259335 12/138756 |
Document ID | / |
Family ID | 37872928 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080259335 |
Kind Code |
A1 |
Raghuraman; Bhavani ; et
al. |
October 23, 2008 |
SPECTROSCOPIC pH MEASUREMENT AT HIGH-TEMPERATURE AND/OR
HIGH-PRESSURE
Abstract
Methods and apparatuses for high-temperature and high-pressure
measurement of pH and/or alkalinity of a fluid is described.
Inventors: |
Raghuraman; Bhavani;
(Wilton, CT) ; Muhammad; Moin; (Alberta, CA)
; Gao; Jinglin; (Edmonton, CA) ; Borman;
Craig; (Camrose, CA) ; Gustavson; Gale;
(Brookfield, CT) ; Rabbito; Philip; (Milford,
CT) |
Correspondence
Address: |
SCHLUMBERGER-DOLL RESEARCH;ATTN: INTELLECTUAL PROPERTY LAW DEPARTMENT
P.O. BOX 425045
CAMBRIDGE
MA
02142
US
|
Assignee: |
Schlumberger Technology
Corporation
Cambridge
MA
|
Family ID: |
37872928 |
Appl. No.: |
12/138756 |
Filed: |
June 13, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11345460 |
Feb 1, 2006 |
7402424 |
|
|
12138756 |
|
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Current U.S.
Class: |
356/402 |
Current CPC
Class: |
Y10T 436/11 20150115;
G01N 21/80 20130101 |
Class at
Publication: |
356/402 |
International
Class: |
G01J 3/46 20060101
G01J003/46 |
Claims
1. An apparatus for high-temperature and high-pressure measurement
of pH of a fluid, the apparatus comprising: a fluid sample chamber
to receive a fluid sample at a measurement pressure in operable
communication with a first pressure regulating means, wherein said
first pressure regulating means is configured to ensure that the
pressure does not drop below the measurement pressure; a dye
chamber in fluid communication with the fluid sample chamber, and
in operable communication with a second pressure regulating means,
wherein said second pressure regulating means is configured to
ensure that the pressure does not drop below the measurement
pressure; a light source and a detector in optical communication
with the interior of the fluid sample chamber; and a spectral
analyzer, wherein the spectral analyzer is configured to analyze
the optical density of a mixture of the fluid sample and dye.
2. The apparatus of claim 1, wherein at least one of the first
pressure regulating means or the second pressure regulating means
is a piston.
3. The apparatus of claim 1, wherein the measurement pressure is
greater than about 1 bar.
4. The apparatus of claim 1, wherein the fluid sample chamber, the
first pressure regulating means, the dye chamber, and the second
pressure regulating means are located in a heating device.
5. The apparatus of claim 4, wherein the heating device is
configured to maintain the apparatus at a measurement
temperature.
6. The apparatus of claim 5, wherein the measurement temperature is
greater than about 323.degree. K.
7. The apparatus of claim 1, wherein the fluid sample chamber
contains a mixer configured to mix the contents of the fluid sample
chamber.
8. An apparatus for high-temperature and high-pressure measurement
of pH of a fluid, the apparatus comprising: a container capable of
withstanding high-pressure and high-temperature; a light source and
a detector in optical communication with the interior of the
high-pressure, high-temperature container; a first pressure
regulator having a first volume chamber in fluid communication with
the high-pressure, high-temperature container, wherein the first
pressure regulator is configured to ensure that the first volume
chamber does not drop below a measurement pressure; a second
pressure regulator having a second volume chamber in fluid
communication with the high-pressure, high-temperature container,
wherein the second pressure regulator is configured to ensure that
the second volume chamber does not drop below said measurement
pressure; a fluid sample container capable of withstanding
high-pressure and high-temperature in fluid communication with the
first volume chamber; a dye reservoir in fluid communication with
the second volume chamber; and a spectral analyzer to receive data
gathered by the detector wherein the spectral analyzer is
configured to analyze the optical density of a mixture of a fluid
sample and a dye.
9. The apparatus of claim 8, further comprising: a water reservoir
in fluid communication with the first volume chamber.
10. The apparatus of claim 8, wherein at least one of the first
pressure regulator and the second pressure regulator is a positive
displacement pump.
11. The apparatus of claim 8, wherein at least one of the first
pressure regulator and the second pressure regulator is a syringe
pump.
12. The apparatus of claim 8, further comprising: a first actuator
in operable communication with the first pressure regulator; a
second actuator in operable communication with the second pressure
regulator; a pressure transducer in fluid communication with the
high-pressure high-temperature container; and a controller in
signal communication with the first actuator, second actuator,
pressure transducer, and spectral analyzer.
13. The apparatus of claim 8, wherein the measurement pressure is
greater than about 1 bar.
14. The apparatus of claim 8, wherein an oven is used to maintain
the temperature equal to a measurement temperature.
15. The apparatus of claim 14, wherein the temperature is greater
than 323.degree. K.
16. A method to obtain total alkalinity of a fluid sample
comprising: a. inputting an acid-dye solution into a dye chamber;
b. inputting water into a fluid sample chamber, wherein the fluid
sample chamber is at a measurement pressure and temperature; c.
measuring the spectrum of the water; d. displacing the water with a
fluid sample, while maintaining measurement pressure; e. measuring
the spectrum of fluid sample; f. inputting an amount of the
acid-dye solution into the fluid sample chamber, while maintaining
measurement pressure; g. measuring a spectrum of the dye solution
and fluid sample mixture; h. determining the pH of the fluid
sample; i. repeating (e), (f), (g), and (h) one or more times to
develop a relationship between pH and acid-volume added to the
fluid sample; and j. determining the alkalinity of the fluid sample
from said relationship.
17. An apparatus for high temperature, high pressure measurement of
pH of a fluid, the apparatus comprising: a flowline to receive a
fluid sample in fluid communication with a process line, wherein
the flowline is configured so that it may be isolated from the
process line; a dye injector in fluid communication with the
flowline, wherein the flowline, process line and dye injector are
maintained at or above a measurement pressure; a light source
located downstream of the dye injector and in optical communication
with the interior of the flowline; and a spectral analyzer in
communication with the detector.
18. The apparatus of claim 17, wherein the measurement pressure is
greater than about 1 bar.
19. The apparatus of claim 17, wherein the dye injector is
configured to inject a dye into the flowing fluid sample.
20. The apparatus of claim 17, wherein the flowline, process line,
and dye injector are maintained at a measurement temperature.
21. The apparatus of claim 20, wherein the measurement temperature
is greater than about 323.degree. K.
Description
TECHNICAL FIELD
[0001] The disclosed method and apparatus relate to pH measurement
of fluids using pH sensitive reagents and, more particularly, to a
method and apparatus that allows accurate pH measurement at
high-temperature and/or high-pressure.
BACKGROUND
[0002] Accurate measurement of pH is important in diverse fields
such as process control, reaction kinetics, environmental and
biomedical research and oilfield applications. Many chemical
processes require pH monitoring and control at extreme conditions
of temperature, pressure, and salinity. However, as will be
described below, standard potentiometric techniques provide
accurate measurements at moderate temperatures, pressures, and
salinities. Measurements of pH of standard buffers at
high-temperature and high-pressure using hydrogen and/or glass
electrodes have been reported by LePeintre, Bull. Soc. Franc.
Electr. 1960, 8, 584, and Kryukov, et al. as cited in pH
Measurement: Fundamentals, Methods, Applications, Instrumentation
VCH Publishers, 1991; however, liquid junction instability results
in uncertainties in the measurement. Furthermore, pressure
balancing needs and liquid junctions make it practically
inconvenient to use hydrogen and/or glass electrodes for routine
measurements in high-pressure, high-temperature systems. Boreng, et
al. in SPE European Formation Damage Conference, May 13-14, 2003,
The Hague, The Netherlands SPE 82199 describe a solid-state
electrode for high-temperature and high-pressure pH measurement.
While this proposed method eliminates the liquid junction
uncertainty, the pH is measured relative to sodium activity that
must be independently determined to determine the absolute pH.
[0003] Spectroscopic measurement of pH with very high accuracy
using pH-sensitive dyes has been a well-established laboratory
technique at ambient conditions since the early 1900's (Bates,
Determination of pH: Theory and Practice, Chapter 6, John Wiley,
1964). More recently, this technique has been shown to improve
precision for seawater and freshwater pH measurements over a range
of ionic strengths where potentiometric techniques can prove to be
problematic (Yao, et al., Environ. Sci. Technol., 2001, 35,
1197-1201; Martz, et al. Anal. Chem., 2003, 75, 1844-1850). These
references cite the advantages of the spectroscopic technique with
respect to low drift, reproducibility, and rapidness of the
measurement as compared to the standard glass electrodes.
Furthermore, because pH measurement depends only on the molecular
properties of the indicator dyes, once the dye equilibrium
dissociation constants have been characterized, the need for
calibration prior to every measurement is eliminated. The methods
described above allow implementation of the spectroscopic technique
at close to ambient conditions and narrow ionic strength intervals
corresponding to either seawater or fresh water conditions,
however, the methods do not allow for implementation of the
spectroscopic technique at high-temperatures and/or
high-pressures.
[0004] Because of the lack of robust high-temperature high-pressure
pH measurement techniques, currently high-temperature and
high-pressure aqueous system equilibrium and the role of pH is
characterized using chemical modeling of complex chemical
equilibria to calculate the pH. In oilfields, it is important to
know the pH of formation fluid to predict corrosion rates, scale
formation, water compatibility, etc. Current practice involves
collecting fluid samples in single-phase bottles, bringing them to
surface and flashing them. The pH at high-temperature high-pressure
downhole conditions is obtained by simulations that use ambient
flashed gas and water phase analysis as inputs to chemical
equilibrium models. This introduces errors in pH measurement due to
sample handling, precipitation of ionic solids from flashed water
samples and modeling uncertainties of complex ionic equilibria.
[0005] Spectroscopic measurement of pH relies on pH-sensitive dyes
that can exist in an acid or base form. The optical absorbance
spectra of pH-sensitive dyes change as they convert from their acid
(A) to base form (B):
AB+H.sup.+ Eq. 1
The fraction of the dye present in the acid and base forms depends
on the pH of the solution. The pH is calculated using the following
equation:
pH = pK a + log .gamma. B .gamma. A + log [ B ] [ A ] , Eq . 2
##EQU00001##
where pK.sub..alpha. is -log.sub.10K.sub..alpha.;
[0006] K.sub..alpha. is the thermodynamic equilibrium constant for
the dye and is a function of temperature and pressure;
[0007] [A] and [B] is the concentration of the acid, base form,
respectively, of the dye in the sample; and
[0008] .gamma..sub.A and .gamma..sub.B is the activity coefficient
of the acid, base form of the dye, respectively, and a function of
temperature, pressure, and ionic strength of solution. Equation 2
is more commonly written as:
pH = pK a ' + log [ B ] [ A ] , where : Eq . 3 pK a ' = - log 10 (
K a .gamma. A .gamma. B ) . Eq . 4 ##EQU00002##
[0009] Because pKa' includes the activity coefficients, it is no
longer only a function of pressure and temperature, but also a
function of ionic strength. Calibration at ambient conditions using
standard buffers of known pH is well established. A two-wavelength
measurement allows calculation of [B]/[A] and hence the
determination of the pH of unknown solutions using Equation 3.
[0010] The challenge is in extending this technique to higher
temperatures and pressures where there are no standard calibrating
buffers. The International Union of Pure and Applied Chemistry
(IUPAC) 2002 guidelines for pH measurement using standard
electrodes are valid only to 50.degree. C., 1 bar, and ionic
strengths below 0.1 gmol/kg (see Buck et al., Measurement of pH
Definition, Standards and Procedures--IUPAC Recommendations 2002,
Pure and Applied Chemistry, 2002, Vol. 74, Issue 11. At higher
temperatures, pressures, and ionic strengths, there are inherent
uncertainties associated with liquid junction potentials; because
of this uncertainty, currently there are no guidelines for making
pH measurements under these conditions. Standard buffer solutions
are typically certified at room temperatures. When buffer solutions
are heated or their salinity (ionic strength) is changed, their pH
values change and as a result they are no longer the original pH
certified standards.
[0011] Raghuraman et al. in Real-Time Downhole pH Measurement Using
Optical Spectroscopy, SPE International Symposium on Oilfield
Chemistry, Feb. 2-4, 2005, Houston, Tex., USA, SPE 93057 describe a
methodology for calibration and extension of the spectroscopic
measurement to higher temperatures and pressures. Standard buffer
solutions are simple salts whose chemical equilibria have been
reported over a range of temperature, pressure, and salinity
conditions. As a first step to calibrating dyes for pH measurements
at high-temperature and high-pressure conditions, one could use
models of standard salt buffer equilibria to calculate pH at these
conditions. Using these pH values for calibration, one can
determine pKa' of various pH-sensitive dyes as a function of
temperature (to 150.degree. C.), pressure (to 680 bar) and ionic
strength (to 3 mol/kg). The dyes chosen should be ones that can
survive and have pH sensitivity under these conditions. Once pKa'
is known, Eq. 3 can be used to calculate pH at any temperature,
pressure, and ionic strength by measuring the dye-sample
spectra.
[0012] Commonly owned Great Britain U.S. Pat. No. 2,395,555,
entitled "Apparatus and Method for Analyzing Downhole Water
Chemistry," incorporated by reference herein in its entirety,
teaches a method of using dyes to measure pH in high temperature
pressure oil wells at downhole conditions.
[0013] Commonly owned United States Patent Application Publication
Number 20040128974, filed Sep. 22, 2003, entitled "Determining
fluid chemistry of formation fluid by downhole reagent injection
spectral analysis," incorporated herein by reference in its
entirety, teaches a method for analyzing formation fluid in earth
formation surrounding a borehole that includes storing analytical
reagent in a container in a fluids analyzer in a formation tester
and moving the formation tester, including the reagent, downhole.
Reagent from the reagent container is injected into formation fluid
in the flow-line to make a mixture of formation fluid and reagent.
The mixture is moved through a spectral analyzer cell in the fluids
analyzer to produce a time-series of optical density measurements
at a plurality of wavelengths. A characteristic of formation fluid
is determined by spectral analysis of the time-series of optical
density measurements.
[0014] Single dyes are typically sensitive to only about 1.5 units
on either side of their pKa. To make measurements over a wide range
of pH, one has to either use many single dyes or alternatively use
a dye mixture. Commonly owned United States Patent Application
Publication Number 20040219064, filed Feb. 19, 2004, entitled
"Spectroscopic pH measurement using optimized reagents to extend
measurement range," incorporated herein by reference in its
entirety, teaches an indicator mixture that allows pH measurement
over a broader range of pH or to a higher accuracy than available
using conventional spectroscopic techniques. In particular, the
mixture of the present invention is comprised of two or more
reagents such that when combined, the reagent mixture is capable of
either detecting: (1) a pH range broader or more accurate than the
reagent individually, or (2) pH more accurately than the reagents
individually. Also disclosed are methods of making and using the
mixture. This methodology allows high-accuracy, extended-range pH
measurement with a single dye mixture (see FIGS. 1 and 2).
Raghuraman et al. in Real-Time Downhole pH Measurement Using
Optical Spectroscopy, SPE International Symposium on Oilfield
Chemistry, Feb. 2-4, 2005, Houston, Tex., USA, SPE 93057 report pH
measurements in high-temperature, pressure oil wells using these
techniques and apparatuses.
[0015] As mentioned earlier, today there is standard IUPAC
recommendation or any spectroscopic method for high-temperature,
high-pressure and high-ionic strength measurement of pH in the
laboratory. Conventional potentiometric techniques work only to
temperatures of 50.degree. C., 1 bar and ionic strength below 0.1
gmol/kg. Thus, there is a need for high-temperature and
high-pressure measurements of pH in the laboratory.
SUMMARY
[0016] In a first embodiment, the present invention relates to an
apparatus for high-temperature and high-pressure measurement of pH
of a fluid, the apparatus comprising: a fluid sample chamber to
receive a fluid sample at a measurement pressure in operable
communication with a first pressure regulating means, wherein the
first pressure regulating means is configured to ensure that the
pressure does not drop below the measurement pressure; a dye
chamber in fluid communication with the fluid sample chamber, and
in operable communication with a second pressure regulating means,
wherein the second pressure regulating means is configured to
ensure that the pressure does not drop below the measurement
pressure; a light source and a detector in optical communication
with the interior of the fluid sample chamber; and a spectral
analyzer, wherein the spectral analyzer is configured to analyze
the optical density of a mixture of the fluid sample and dye.
[0017] In a second embodiment, a method of high-temperature and
high-pressure measurement of pH of a fluid is further disclosed,
the method comprising: a. inputting an amount of dye solution into
a dye chamber; b. inputting an amount of water into a fluid sample
chamber; c. adjusting the pressure of the dye solution and the
water to a measurement pressure; d. measuring a spectrum of the
water; e. displacing the water with the fluid sample, while
ensuring that the pressure does not drop below the measurement
pressure; f. measuring a spectrum of the fluid sample; g. inputting
a desired amount of the dye solution into the fluid sample chamber;
and h. measuring a spectrum of the dye solution and the fluid
sample mixture. Further, the pH of the fluid sample may be
determined using the measured spectrum.
[0018] In a third embodiment, an apparatus for high-temperature and
high-pressure measurement of pH of a fluid, the apparatus
comprising: a container capable of withstanding high-pressure and
high-temperature; a light source and a detector in optical
communication with the interior of the high-pressure,
high-temperature container; a first pressure regulator having a
first volume chamber in fluid communication with the high-pressure,
high-temperature container, wherein the first pressure regulator is
configured to ensure that the first volume chamber does not drop
below a measurement pressure; a second pressure regulator having a
second volume chamber in fluid communication with the
high-pressure, high-temperature container, wherein the second
pressure regulator is configured to ensure that the second volume
chamber does not drop below the measurement pressure; a fluid
sample container capable of withstanding high-pressure and
high-temperature in fluid communication with the first volume
chamber; a dye reservoir in fluid communication with the second
volume chamber; and a spectral analyzer to receive data gathered by
the detector wherein the spectral analyzer is configured to analyze
the optical density of a mixture of a fluid sample and a dye to
determine the pH of the fluid sample.
[0019] In a fourth embodiment, a method of high temperature and
high pressure measurement of pH of a fluid is further disclosed,
the method comprising: a. filling lines, pump cylinders, and a
container capable of withstanding high temperature and high
pressure with water at a measurement pressure; b. measuring the
spectrum of the water; c. displacing at least a portion of the
water with a fluid sample at measurement pressure, while ensuring
that the pressure does not drop below the measurement pressure; d.
measuring the spectrum of the fluid sample at measurement pressure;
e. mixing a known amount of a dye solution with the fluid sample,
while ensuring that the pressure does not drop below the
measurement pressure; and f. measuring the spectrum of the
dye/fluid sample mixture at measurement pressure. Further, the pH
of the dye/fluid sample mixture may be determined from the spectrum
of the dye/fluid sample mixture.
[0020] In a fifth embodiment, a method to obtain total alkalinity
of a fluid sample is disclosed, comprising: a. inputting an
acid-dye solution into a dye chamber; b. inputting water into a
fluid sample chamber, wherein the fluid sample chamber is at a
measurement pressure and temperature; c. measuring the spectrum of
the water; d. displacing the water with a fluid sample, while
maintaining measurement pressure; e. measuring the spectrum of
fluid sample; f. inputting an amount of the acid-dye solution into
the fluid sample chamber, while maintaining measurement pressure;
g. measuring a spectrum of the dye solution and fluid sample
mixture; h. determining the pH of the fluid sample; i. repeating
(e), (f), (g), and (h) one or more times to develop a relationship
between pH and acid-volume; j. determining the alkalinity of the
fluid sample from the relationship.
[0021] In a sixth embodiment, an apparatus for high temperature,
high pressure measurement of pH of a fluid is disclosed, the
apparatus comprising: a flowline to receive a fluid sample in fluid
communication with a process line, wherein the flowline is
configured so that it may be isolated from the process line; a dye
injector in fluid communication with the flowline, wherein the
flowline, process line and dye injector are maintained at or above
a measurement pressure; a light source located downstream of the
dye injector and in optical communication with the interior of the
flowline; and a spectral analyzer in communication with the
detector.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The present disclosure will be better understood by those
skilled in the pertinent art by referencing the accompanying
drawings, where like elements are numbered alike in the several
figures, in which:
[0023] FIG. 1 is a plot showing the spectra (optical density (OD)
versus wavelength) of a three-reagent mixture in buffer solution
with pH varying from 3 to 9.
[0024] FIGS. 2(a) and (b) are plots: (a) comparing model predicted
pH from experimental optical density ratios (ODR) values of FIG. 1
with true buffer pH values (445 and 570 nm wavelengths) and (b)
showing the error in pH measurements as a function of pH.
[0025] FIG. 3 is a schematic view of a piston/chamber embodiment of
the present invention for spectroscopic pH measurement at
high-temperature and high-pressure.
[0026] FIG. 4 is a flowchart illustrating an embodiment of a method
of the present invention for spectroscopic pH measurement at
high-temperature and high-pressure that may be used with the
embodiment shown in FIG. 3.
[0027] FIG. 5 is a flowchart illustrating an embodiment of a method
of the present invention for determining alkalinity of a fluid at
high-temperature and high-pressure.
[0028] FIG. 6 is a schematic view of a syringe pump embodiment of
the present invention for spectroscopic pH measurement at
high-temperature and high-pressure.
[0029] FIG. 7 is a flowchart illustrating an embodiment of the
method of the present invention for spectroscopic pH measurement at
high-temperature and high-pressure.
[0030] FIG. 8 is a schematic view of an "in flow" embodiment of the
disclosed apparatus of the present invention for spectroscopic pH
measurement at high-temperature and high-pressure.
DETAILED DESCRIPTION
[0031] Throughout the present disclosure the terms reagent and dye
are used interchangeably.
[0032] FIG. 1 shows experimentally measured spectra for a
three-reagent mix in pH buffers 3-9. Arrow A indicates decrease in
OD of acid forms of reagents as buffer pH increases from 3 to 9.
Arrow B indicates increase in OD of base forms of the reagents as
buffer pH increases from 3 to 9.
[0033] FIG. 2(a) compares model-predicted pH values calculated
using measured ODR values of FIG. 1 with true pH values of the
buffer solutions. Properties of the reagents used in the mixture
are summarized in Table 1. FIG. 2(b) is a plot of the experimental
error at various pH values. The reagent mixture of the example of
FIG. 2(b) is accurate over the range of buffers used (pH 3-9) with
the errors within 0.06 pH units. Accordingly, the reagent mixture
used in the apparatus and methodology of the present invention is
accurate over a broader pH range than the traditional single
reagent indicators, which typically work over 2-3 pH units (see,
for example, Table 2 below).
TABLE-US-00001 TABLE 1 Summary of reagent properties used in the
model of FIG. 2a. Phenol Red Chlorophenol Red Bromophenol Blue
(reagent 1) (reagent 2) (reagent 3) Acid Base* Acid Base* Acid
Base* .epsilon. at 570 nm (.lamda..sub.2) 108 37975 58 54247 378
46859 .epsilon. at 445 nm (.lamda..sub.1) 17916 3352 18136 1985
21711 1981 Mol. wt. 354.38 376.36 423.28 445.26 669.98 691.97 pKa
7.79 6.11 4.11 *The base form is a sodium salt of the reagent.
TABLE-US-00002 TABLE 2 Extending range of pH measurements with
reagent mixtures for 0.1 pH unit desired accuracy assuming
spectroscopic noise of 0.01 OD units Reagent Mole Fraction
(f.sub.1, f.sub.2, f.sub.3) C.sub.T, [M] pH range Phenol Red (PR)
1.0, 0.0, 0.0 2 .times. 10.sup.-5 6.6-8.7 Chlorophenol Red (CPR)
0.0, 1.0, 0.0 2 .times. 10.sup.-5 4.7-7.0 Bromophenol Blue (BB)
0.0, 0.0, 1.0 2 .times. 10.sup.-5 2.8-5.1 PR-CPR 0.55, 0.45, 0.0
(equal weight fractions) 2 .times. 10.sup.-5 5.1-8.2 PR-CPR 0.55,
0.45, 0.0 (equal weight fractions) 4 .times. 10.sup.-5 4.8-8.6
PR-CRP-BB 0.42, 0.35, 0.23 (equal weight fractions) 2 .times.
10.sup.-5 3.6-7.9 PR-CRP-BB 0.46, 0.26, 0.28 (optimized for pH 3.5
to 8) 2 .times. 10.sup.-5 3.5-8.1 PR-CRP-BB 0.42, 0.35, 0.23 (equal
weight fractions) 4 .times. 10.sup.-5 3.2-8.5
[0034] FIG. 3 shows an embodiment of the disclosed apparatus 280
for spectroscopic pH measurement at high-temperature and
high-pressure in a laboratory environment. A first pressure
regulating means 284 and fluid sample chamber 288 are shown. The
first pressure regulating means may be a device such as a fluid
sample piston. The fluid sample chamber 288 has a fluid sample
chamber inlet/outlet 289 which allows fluid sample to be pumped
into the chamber 288 or removed from the chamber 288. The fluid
sample chamber inlet/outlet 289 has a valve 290 that controls the
inflow and outflow of fluid into the chamber 288. The pressure
regulating means 284 is in operable communication with an actuator
292. The fluid sample chamber 288 may have a mixer means 296 in
fluid communication with it. The mixer means 296 may mix the fluid
using mixing or shaking techniques. The fluid sample chamber 288 is
in optical communication with a spectral analyzer 300. A light
source 304 may be controlled by the spectral analyzer 300. The
light source may transmit light through a fiber optic line 312 to a
first optical port 308 located on the chamber 288. The fiber optic
line provides optical communication between the chamber interior
and the light source 304. In alternative embodiments, the light
source may be located adjacent to the optical port 308 or may be
located within the chamber 288. Spectral information from the fluid
sample chamber 288 may be transmitted through a second optical port
316 through a fiber optic line 320 to a detector (not shown). A
spectral analyzer 300 analyzes data obtained by the detector. It
should be obvious to one of ordinary skill in the art that other
configurations for locations and communications between the light
source and detector are available with respect to the disclosed
apparatus.
[0035] The fluid sample chamber 288 is in fluid communication with
a dye chamber 324 via a line 336. The line has a valve 340. The dye
chamber 324 is in operable communication with a second pressure
regulating means 328. The second pressure regulating means may be a
dye piston. The dye chamber 324 has a dye chamber inlet/outlet 325
which allows for dye to be placed in or removed from the chamber
324. The dye chamber inlet/outlet 325 has a valve 326 that controls
the inflow and outflow of fluid into the chamber 324. The second
pressure regulating means 328 is in operable communication with an
actuator 330. The chambers 288 and 324 are located in an oven 334,
or any other suitable heating device, which can be configured to
heat the contents of the chambers 288, 324 and to control the
measurement temperature. The pressure and volume within the dye
chamber 324 and fluid sample chamber 288 are controlled and
adjusted by the pressure regulating means 328, 284, respectively
(in this embodiment, the position of the pistons). The fluid flow
schemes are controlled by opening and closing the valves 270, 326,
340 and operating the pistons 284, 328. Of course, one of ordinary
skill in the art will understand that other types of pumps may be
used in this embodiment, including, but not limited to syringe type
pumps.
[0036] FIG. 4a shows a flowchart illustrating an embodiment of the
disclosed method for spectroscopic pH measurement at
high-temperature and high-pressure. This method may be used in
association with the apparatus shown in FIG. 3. At act 350, a dye
solution is inputted into the dye chamber. At act 354, water
(preferably deionized water) is inputted into the fluid sample
chamber. At act 358, the pressure of the dye solution and water is
adjusted to the desired pressure (also referred to as the
"measurement pressure"). These pressure adjustments may of course
be accomplished with the first pressure regulating means 284 and
the second pressure regulating means 328. At act 362 (optional),
the temperature of the dye solution and water is adjusted to a
desired temperature (also referred to as the "measurement
temperature"), such as with the oven 334. At act 366, the spectrum
of the water is measured, to obtain a baseline spectrum of the
water, and may be used to verify that the spectral analyzer is
operating properly. At act 370, a fluid sample at measurement
temperature and pressure displaces the water while ensuring that
the pressure does not drop below the measurement pressure. It is
noted that displacement of the water with the fluid sample is one
non-limited method to ensure that the appropriate pressure is
maintained. One skilled in the art would appreciate that additional
methodologies and apparatuses may be used. The fluid sample is of
course the fluid of interest for which pH readings at high-pressure
and high-temperature is desired. At act 374 the spectrum of the
fluid sample at measurement temperature and pressure is measured.
This spectrum may be used as a baseline for comparison with the
spectrum of the fluid sample and dye solution mixture. At act 378,
a desired amount of dye solution is inputted into the fluid sample
chamber, again while ensuring that the measurement pressure is
maintained. At act 380, the mixer 296 may be operated to mix the
dye solution and fluid sample together. At act 382, a spectrum of
the dye solution and fluid sample is measured. Based on the
spectra, the pH of the fluid sample can be determined at act 384.
If pressure and temperature sensitivity information is desired, the
steps in either or both of FIGS. 4b and 4c may be incorporated.
[0037] Referring now to FIG. 4b, at act 386, the pressure of the
fluid sample and dye is adjusted. At act 390, the spectrum of the
dye solution and fluid sample mixture is measured. At this point,
acts 386 and 390 may be repeated in order to develop enough data
points so that at act 394, the pressure sensitivity of pH for the
fluid sample may be determined. Referring now to FIG. 4c, at act
398, the temperature of the dye solution and fluid sample mixture
may be adjusted. At act 402, the spectrum of the dye solution and
fluid sample mixture may be measured. And, acts 398 and 402 may be
repeated in order to develop enough data points so that at act 406,
the temperature sensitivity of pH for the fluid sample may be
measured. One of ordinary skill in the art will recognize that
temperature sensitivity measurements and pressure sensitivity
measurements need not be both performed, nor does one need to be
performed after or before the other. It should be noted that
changing the pressures and temperatures may cause phase transitions
in the fluid sample, which may lead to measurable changes in pH
that may be of interest in certain applications. Thus, phase
sensitive pH measurements may also be obtained and characterized
using the methods of the present invention.
[0038] One of ordinary skill in the art will recognize that many
tests can be developed using the disclosed apparatus to generate
the pH profile of a high-temperature and/or high-pressure fluid as
a function of temperature, pressure, and amount of solution gas
(i.e. when pressure is reduced to below the bubble point pressure
and solution gas is discharged from the fluid). Additionally, the
high-temperature and/or high-temperature pH profile may be
developed for a commingling of two or more liquid streams.
Similarly tests may be run to determine the pH profile for various
compositions at high-temperature and/or high-pressure.
[0039] Standard laboratory methods for the determination of total
alkalinity of a fluid typically involves titrating a known volume
of the fluid with an acid in the presence of a calorimetric
indicator (such as methyl purple) or a potentiometric electrode.
Total alkalinity is defined as the point in the titration curve
where all carbonate species are neutralized to undissociated
carbonic acid or dissolved CO.sub.2 (also referred to as the "end
point") and is typically found at a pH of about 4.5. With a
calorimetric indicator like methyl purple, the end point
corresponds to a color change from green to purple, which can be
monitored spectroscopically. Alternatively, if pH measurements are
also recorded continuously with acid addition, inflections in the
titration curves (pH vs. volume of acid added) can also be used to
calculate hydroxide alkalinity and carbonate alkalinity in addition
to total alkalinity using standard methods reported in literature
(see Langmuir, Aqueous Environmental Geochemistry, Prentice-Hall,
Inc. 1997). This calculation method can then be used to estimate
the total carbonate and bicarbonate concentration in the sample as
well. Currently, there are no means to measure alkalinity for
high-temperature and pressure samples.
[0040] The current method and apparatus can be modified to conduct
such a titration at high-temperature and high-pressure to measure
alkalinity. One could use an acid-dye solution mixture in the dye
chamber 324 (see FIG. 3) and charge the fluid sample chamber 288
with a sample fluid. Small fixed volumes of acid-dye solution can
be added to the fluid sample chamber 288. Either a calorimetric dye
like methyl purple could be used for determining the end point with
color change, or an acid-dye mix could be used to record pH
simultaneously during the titration to determine the inflection
point. When the end point is reached, the total volume of acid
added is known because the exact amount of acid-dye solution
transmitted from the chamber 324 to the fluid sample chamber 288 is
known.
[0041] FIG. 5 shows a flowchart illustrating an embodiment of the
disclosed method for titration at high-temperature and
high-pressure to obtain total alkalinity. This method may be used
in association with the apparatus shown in FIG. 3. At act 410, an
acid-dye solution is inputted into the dye chamber 324. The dye is
preferably a dye mixture that allows extended range pH measurement
as described above. At act 414, water (again, preferably deionized
water) is inputted into the fluid sample chamber 288. At act 418,
the pressure of the acid-dye solution and water is adjusted to the
measurement pressure. This pressure adjustment may of course be
accomplished with the first pressure regulating means 284 and the
second pressure regulating means 328. At act 422, the temperature
of the acid-dye solution and water is adjusted to a measurement
temperature. This temperature adjustment may be accomplished using
oven 334. At act 424, the spectrum of the water is measured to
obtain a baseline spectrum of the water, which may be used to
verify that the spectral analyzer 300 is operating properly. At act
428, a fluid sample at measurement temperature and pressure
displaces the water while ensuring that the pressure does not drop
below the measurement pressure. The fluid sample is of course the
fluid of interest for which a total alkalinity measurement at
high-pressure and high-temperature is desired. At act 432 the
spectrum of the fluid sample is measured. This spectrum may be used
as a baseline for comparison with the spectrum of the fluid sample
and acid-dye solution mixture. At act 438, an amount of acid-dye
solution is inputted into the fluid sample chamber 288, again while
ensuring that the pressure does not drop below the measurement
pressure. During this act, the mixer 296 may be operated to mix the
dye solution and fluid sample together. At act 442, a spectrum of
the acid-dye and fluid sample mixture (in chamber 288) is measured.
Based on the spectra, the pH of the acid-dye fluid sample mixture
can be determined at act 446 and the relationship between pH and
volume of the acid-dye solution added to the fluid sample chamber
is developed at act 448. It is noted that acts 438, 442, and 446
may be repeated to acquire data to develop the relationship of 448.
One output of this relationship may be a titration curve. At act
450, the relationship between pH and acid volume is analyzed to
determine if the end point has been reached. If the end point has
been reached, then the total alkalinity of the original fluid
sample can be determined (at act 454) from the amount of acid added
to the fluid sample. Further, intermediate inflection points may be
used to determine the hydroxide and carbonate alkalinity as
described earlier.
[0042] A second embodiment of the apparatus of the present
invention 532 for spectroscopic pH measurement at high-temperature
and high-pressure is shown in FIG. 6. In this embodiment the
apparatus 532 comprises a high-pressure high-temperature container
536 in optical communication with a spectral analyzer 540. The
spectral analyzer 540 may contain a light source 541 and a detector
543. A data transmission means 545, such as, but not limited to
fiber optic lines, allow communication between the light source 541
and the interior of the container 536, as well as communication
between the detector 543 and the interior of the container 536. It
should be obvious to one of ordinary skill in the art that other
configurations for location of the light source 541 and detector
543 are available with respect to the disclosed apparatus. The
spectral analyzer 540 is configured to spectrally analyze the light
transmitted through the container 536. A fluid sample container
542, water reservoir 544, and dye reservoir 548 are all in fluid
communication with the container 536. The water held in the water
reservoir is preferably deionized water. A first pressure regulator
means 552 having a volume chamber 552' to hold a fluid is in fluid
communication with and located between the high-temperature and
high-pressure container 536 on the one hand, and the fluid sample
container 542 and water reservoir 544 on the other. A second
pressure regulator means 556 having a volume chamber 556' to hold a
fluid is in fluid communication with and located between the dye
reservoir 548 and the high-pressure high-temperature container 536.
The pressure regulators 552, 556 may be any suitable means, such as
pumps, including but not limited to, syringe or piston type pumps.
The pressure regulators 552,556 are in communication with actuators
560, 564. Valves 568, 572, 576, 580, 584, 592, 546, 600 are located
throughout the system to isolate various components and to allow
the delivery of fluids to and from the high-pressure,
high-temperature container 536 at different controlled pressures. A
pressure transducer 604 is in fluid communication with the
high-pressure high-temperature container 536. The actuators 560,
564, valves 546 through 600, pressure transducer 604 and spectral
analyzer 540 may each be in signal communication with a controller
(not shown) that is configured to open and close the various
valves, and operate the pressure regulators 552, 556 such that
fluids at specified pressures, specified temperatures, and
specified combinations, mixtures or individual doses of fluid
sample, water, and dye may be delivered to the high-pressure
high-temperature container 536. In an alternative embodiment, the
entire apparatus 532, except for the spectral analyzer 540,
pressure regulators 552, 556, and controller may be located in an
oven or heat jacket to provide controlled heat to the apparatus
532. In still other embodiments, other controllable heat sources
may be used to heat the apparatus 532 such as but not limited to
heating elements.
[0043] FIG. 7a shows a flowchart illustrating one embodiment of the
disclosed method for spectroscopic pH measurement at
high-temperature and high-pressure. This method may be used in
association with the apparatus shown in FIG. 6. At act 610, the
lines (except the lines in the dye section to the left of valve 576
in FIG. 6--it is noted that reference to "left" is used for
convenience in reference to the configuration shown in FIG. 6),
pump chambers 556' and 552', and the high-pressure high-temperature
container 536 is filled with water (preferably deionized water). At
act 614, the pressure is adjusted to the measurement pressure. At
act 618, the spectrum of the water is measured. This may be done in
order to obtain a baseline spectrum of water and may be used to
verify that the spectral analyzer is operating properly. At act
622, a fluid sample at measurement pressure is inputted into lines
and volume chamber 552' and the high pressure high temperature
container 536 to displace the water while ensuring that the
pressure does not drop below the measurement pressure. As described
in previous embodiments, one non-limiting method of ensuring that
the measurement pressure is maintained is to displace the water in
certain lines, a volume chamber, and the high-pressure,
high-temperature chamber 536 with the fluid sample. The fluid
sample is that fluid for which pH measurement is ultimately
desired. The pressure of the fluid sample is to be maintained at
the measurement pressure. At act 630, the spectrum of the fluid
sample is measured. This spectrum may be used as a baseline for
comparison with the spectrum of the fluid sample and dye mixture.
At act 634, an amount of dye is withdrawn from the dye reservoir
and used to fill the lines and volume chamber in the section to the
left of valve 576 at measurement pressure. (Alternatively, if the
system is not at measurement pressure, the system may then be
pressurized to the measurement pressure.) At act 638, the
pressurized dye is mixed with the fluid sample. The mixing may be
accomplished by operating valves as required to pump dye from the
pump 556 into the chamber 552', where the dye begins mixing with
the sample. Then the dye/sample can be sent from the first volume
chamber 552' back to the second volume chamber 556', thereby
providing more mixing of the dye and sample. Of course, the sample
may first be sent into second volume 556' to mix with the dye, and
then the dye/sample can be sent back to the first volume 552'. At
act 642, the dye and fluid sample are allowed to mix over a period
of time. The period of time will depend on the amount of time
necessary for the dye and fluid sample to properly mix and allow
for meaningful measurements. The fluid in the lines and the
high-pressure high-temperature container is then displaced while
maintaining measurement pressure by the dye/sample fluid mixture at
act 642. At act 646, the spectrum of the dye and fluid sample
mixture is measured at measurement pressure. Based on the spectra,
the pH of the fluid sample can be determined at act 650. If more
information about the sample fluid is desired, more measurements
may be made, which are discussed with respect to FIGS. 7b and
7c.
[0044] Referring now to FIG. 7b, at act 654, the pressure of the
fluid sample and dye is adjusted. At act 658, the spectrum of the
dye and fluid sample mixture is measured. At this point, acts 654
and 658 may be repeated in order to develop enough data points so
that at act 662, the pressure sensitivity of pH for the fluid
sample may be determined. Now referring to FIG. 7c, at act 666, the
temperature of the dye and fluid sample mixture may be adjusted. At
act 670, the spectrum of the dye and fluid sample mixture may be
measured. And, acts 666 and 670 may be repeated in order to develop
enough data points so that at act 674, the temperature sensitivity
of pH for the fluid sample mixture may be determined. It should be
noted that it may be desirable to maintain pressure at some
percentage higher than desired measurement pressure (such as 10%
higher, for example) while replacing and mixing the fluids to
ensure that during displacements and mixing the pressure never
accidentally drops below measurement pressure. If the fluids drop
below measurement pressure, this may cause any dissolved gas to
come out of solution and that can change the sample and its pH.
[0045] The system may be adjusted to any desired measurement
temperature by using the heating element described in connection
with FIG. 6.
[0046] FIG. 8 shows an "in-flow" embodiment of an apparatus 700 for
spectroscopic pH measurement at high-temperature and high-pressure.
The apparatus comprises a flowline 704. The flowline 704 may be in
fluid communication with a process line 706, wherein the pH of the
fluid in the process is monitored and/or pH determined. Valves 707a
and 707b may be located on the flowline 704 to isolate the
apparatus 700 from the process line 706. In the embodiment shown in
FIG. 8, the flowline 704 is shown connecting back with the process
line 706 via the downstream valve 707b. The sample travels in the
flowline in the direction of the arrow. A dye injector 708 is
located on the flowline 704 and is configured to inject a dye 712
into the flowline 704 to mix with the flowing fluid sample. A light
source 716 is located downstream from the dye injector 708. The
light source may be external to the flowline 704, but adjacent to
an optical port 720, such as a window for instance, located on the
flowline. The port 720 is configured to allow light from the light
source 716 to enter the flowline 704. A detector 724 is located
downstream of the dye injector, and generally opposed to the light
source 716. The detector is configured to obtain data from the
light emanating from the light source 716 and traveling through the
sample and dye 712 mixture. The detector 724 may transmit the data
to a spectral analyzer, or the detector 724 may itself have
spectral analyzing capacity. The detector 724 may be external to
the flowline 704 and adjacent to the optical port 728 as shown in
FIG. 8, or alternatively may be located on the flowline 704. The
optical port is configured to allow light to exit the flowline 704
and enter the detector 724. All the components in fluid
communication with the flowline 704 should be rated for
high-temperature and high-pressure. The apparatus 700 may be used
for high-temperature and/or high-pressure continuous flow processes
and reaction systems where online pH monitoring is needed. The
apparatus 700 may use periodic dye injection into the flowline 704
to allow for in situ pH measurements. Such in situ pH measurements
may be used with feedback control loops for pH control in processes
and reactions where pH is required to be maintained at prescribed
levels. In another embodiment, flowline 704 may simply be routed to
a disposal means (not shown) via downstream valve 707b, hence
allowing a sample to be withdrawn from the process line 706 and
then disposed of once the pH measurement is completed, if one
wishes to avoid downstream contamination of the process sample with
the dye.
[0047] The disclosed high-temperature high-pressure pH measuring
apparatus and method of the present invention has many advantages.
The apparatuses and methods allow for the accurate measuring of pH
at extreme conditions. The disclosed apparatus allows for accurate
mixing of dye and fluid samples at extreme conditions in order to
determine the pH of the fluid sample. Additionally, the disclosed
methods and apparatuses allow for the titration of fluids at
high-temperature and high-pressure.
[0048] It should be noted that the terms "first", "second", and
"third", and the like may be used herein to modify elements
performing similar and/or analogous functions. These modifiers do
not imply a spatial, sequential, or hierarchical order to the
modified elements unless specifically stated.
[0049] While the disclosure has been described with reference to
several embodiments, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiments disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *