U.S. patent application number 14/653272 was filed with the patent office on 2016-02-11 for pressure volume temperature system.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Shunsuke Fukagawa, Christopher Harrison, Robert J Schroeder, Elizabeth Smythe, Matthew T. Sullivan.
Application Number | 20160040533 14/653272 |
Document ID | / |
Family ID | 51625001 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160040533 |
Kind Code |
A1 |
Harrison; Christopher ; et
al. |
February 11, 2016 |
Pressure Volume Temperature System
Abstract
A method and an apparatus for characterizing a fluid including a
phase transition cell to receive the fluid, a piston to control
fluid pressure, a pressure gauge to measure the fluid pressure and
to provide information to control the piston, and connectors to
connect the cell, piston, and gauge. The exterior volume of the
phase transition cell, piston, gauge, and connectors is less than
about 10 liters. A method and an apparatus to characterize a fluid
including observing a fluid in an phase transition cell, measuring
a pressure of the fluid, and adjusting a pressure control device in
response to the measuring.
Inventors: |
Harrison; Christopher;
(Auburndale, MA) ; Sullivan; Matthew T.;
(Westwood, MA) ; Smythe; Elizabeth; (Cambridge,
MA) ; Fukagawa; Shunsuke; (Arlington, MA) ;
Schroeder; Robert J; (Newtown, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
51625001 |
Appl. No.: |
14/653272 |
Filed: |
February 10, 2014 |
PCT Filed: |
February 10, 2014 |
PCT NO: |
PCT/US2014/015467 |
371 Date: |
June 18, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61785504 |
Mar 14, 2013 |
|
|
|
Current U.S.
Class: |
73/152.05 ;
73/152.02; 73/152.12 |
Current CPC
Class: |
E21B 49/10 20130101;
E21B 49/081 20130101; E21B 47/06 20130101; E21B 49/0875 20200501;
E21B 49/088 20130101 |
International
Class: |
E21B 49/08 20060101
E21B049/08 |
Claims
1. An apparatus for characterizing a fluid, comprising: a phase
transition cell to receive the fluid; a piston to control pressure
of the fluid; a pressure gauge to measure the pressure of the fluid
and to provide information to control the piston; at least one
measurement sensor to measure a property of the fluid; and
connectors to fluidly connect the cell, piston, and pressure gauge,
wherein the apparatus utilizes a total fluid volume of about 1.0 mL
or less.
2. The apparatus of claim 1, further comprising a membrane.
3. The apparatus of claim 2, wherein the membrane prevents
particles with a dimension of 10 microns or greater to flow through
the membrane.
4. The apparatus of claim 2, wherein the measurement sensor is
selected from the group consisting of a densitometer and a
viscometer.
5. The apparatus of claim 1, wherein the at least one measurement
sensor comprises a densitometer.
6. The apparatus of claim 1, wherein the at least one measurement
sensor comprises a viscometer.
7. The apparatus of claim 1, further comprising a membrane, a
densitometer, a viscometer, an inlet valve, and an exit valve.
8. The apparatus of claim 7, wherein the fluid flows through the
membrane, then the inlet valve, then the phase transition cell,
then the densitometer, then the viscometer, then the pressure
gauge, then the piston, then the exit valve.
9. The apparatus of claim 1, wherein the fluid has a total fluid
volume of about 0.5 mL or less.
10. The apparatus of claim 1, wherein the connectors electrically
isolate when forming a fluidic connection.
11. The apparatus of claim 1, wherein the connectors have a total
internal volume of less than 1 mL.
12. The apparatus of claim 1, wherein the connectors comprises
tubing.
13. The apparatus of claim 12, wherein the tubing has an internal
diameter of about 1.0 mm or less.
14. The apparatus of claim 13, wherein ends of the tubing comprise
isolation components.
15. The apparatus of claim 1, wherein the cell, piston, and
pressure gauge have a fluid volume less than about 2 ml.
16. The apparatus of claim 1, wherein the pressure gauge has a dead
volume of less than 0.5 ml.
17. The apparatus of claim 1, wherein the volume of the apparatus
is configured to fit in a wellbore.
18. The apparatus of claim 24, wherein the volume is contained in a
cylindrical shaped housing with an inner diameter of 3.875 inches
or less.
19. The apparatus of claim 1, further comprising a Peltier
cooler.
20. A method to characterize a fluid, comprising: observing a fluid
in a phase transition cell; measuring a pressure of the fluid in
the cell; and adjusting a pressure control device in response to
the measuring, wherein the external volume of the phase transition
cell, piston, and gauge is less than 10 liters.
21. The method of claim 20, wherein the depressurization or
pressurization rate of the fluid is less than 200 psi/second.
22. The method of claim 20, wherein the fluid is circulated through
the system at a volumetric rate of no more than 1 ml/sec.
23. The method of claim 20, further comprising measuring a
temperature.
24. The method of claim 20, further comprising adjusting the
temperature.
25. The method of claim 24, wherein adjusting the temperature
comprises increasing the fluid flow through the cell.
26. The method of claim 25, wherein adjusting the temperature
comprises a Peltier cooler.
Description
BACKGROUND
[0001] The oil and gas industry has developed various tools capable
of determining formation fluid properties. For example, borehole
fluid sampling and testing tools such as Schlumberger's Modular
Formation Dynamics Testing (MDT) Tool can provide important
information on the type and properties of reservoir fluids in
addition to providing measurements of reservoir pressure,
permeability, and mobility. These tools may perform measurements of
the fluid properties downhole, using sensor modules on board the
tools. These tools can also withdraw fluid samples from the
reservoir that can be collected in bottles and brought to the
surface for analysis. The collected samples are routinely sent to
fluid properties laboratories for analysis of physical properties
that include, among other things, oil viscosity, gas-oil ratio,
mass density or API gravity, molecular composition, H.sub.2S,
asphaltenes, resins, and various other impurity concentrations.
[0002] The reservoir fluid may break phase in the reservoir itself
during production. For example, one zone of the reservoir may
contain oil with dissolved gas. During production, the reservoir
pressure may drop to the extent that the bubble point pressure is
reached, allowing gas to emerge from the oil, causing production
concerns. Knowledge of this bubble point pressure may be helpful
when designing production strategies
[0003] Characterizing a fluid in a laboratory utilizes an arsenal
of devices, procedures, trained personnel, and laboratory space.
Successfully characterizing a fluid in a wellbore uses methods,
apparatus, and systems configured to perform similarly with less
space and personal attention and to survive in conditions that
quickly destroy traditional lab equipment. Identifying the
undesired phase change properties of a fluid is especially useful
when managing a hydrocarbon reservoir.
SUMMARY
[0004] Embodiments herein relate to a method and an apparatus for
characterizing a fluid including a phase transition cell to receive
the fluid, a piston to control fluid pressure as the fluid flows
from the cell, a pressure gauge to measure the fluid pressure and
to provide information to control the piston, and connectors to
connect the cell, piston, and gauge. Embodiments herein relate to a
method and an apparatus to characterize a fluid including observing
a fluid in an phase transition cell, measuring a pressure of the
fluid during pressurization or depressurization, and adjusting a
pressure control device in response to the measuring.
FIGURES
[0005] FIG. 1 is a schematic of a drilling system according to
embodiments herein.
[0006] FIG. 2 is a flow chart of one embodiment of a process
according to embodiments herein.
[0007] FIG. 3 is schematic drawings of an embodiment of an
experimental PVT apparatus, including a phase transition cell for
saturation pressure detection with optical measurements, a
microfluidic vibrating tube densitometer for density measurements,
and a microfluidic vibrating wire viscometer for viscosity
measurements for use downhole.
[0008] FIG. 4 is a sectional view of an o-ring, backup ring, metal
flange, and electrically isolating backup ring according to
embodiments herein.
[0009] FIG. 5 is a sectional view of a vibrating tube densitometer
with integrated isolation components according to embodiments
herein.
[0010] FIG. 6 is a sectional view of a sensor block containing
modular sensors according to embodiments herein.
[0011] FIGS. 7A and 7B are embodiments of a breadboard `plug and
play` based microfluidic system allowing sensors to be replaced and
exchanged according to embodiments herein.
[0012] FIG. 8 is a sectional schematic view of a fluid path for
`direct connect` sensor configuration. according to embodiments
herein
[0013] FIGS. 9A and 9B are a sectional view of a fluidic connector
and a schematic of a receiving element according to embodiments
herein.
[0014] FIGS. 10A and 10B are sectional views of two embodiments of
O-rings disposed on connectors according to embodiments herein.
[0015] FIG. 11 is a schematic diagram of alignment pins and holes
to facilitate sensor and jumper attachments according to
embodiments herein.
[0016] FIG. 12 is a plot of pressure and temperature as a function
of time for test conditions according to embodiments herein.
[0017] FIGS. 13A, 13B, and 13C are schematic diagrams of `plug and
play` and `direct connect` based microfluidic system fluid paths
according to embodiments herein.
[0018] FIG. 14 is a schematic of an embodiment comprising a Peltier
cooler according to embodiments herein.
[0019] FIG. 15 is a schematic drawing of an embodiment of an
experimental PVT apparatus, including a phase transition cell for
saturation pressure detection with optical measurements, a
microfluidic vibrating tube densitometer for density measurements,
and a microfluidic vibrating wire viscometer for viscosity
measurements.
[0020] FIG. 16A is an embodiment of the optical signal density of
the measured signal during depressurization when thermal nucleation
was applied and not applied according to embodiments herein.
[0021] FIG. 16B shows density and viscosity measurements during
depressurization shown in FIG. 15.
[0022] FIG. 17 is a phase diagram measured of a multi alkane sample
with and without thermal nucleation of the sample fluid according
to embodiments herein.
[0023] FIG. 18A is a plot of the difference of the saturation
pressure measured with and without thermal nucleation as a function
of temperature according to embodiments herein.
[0024] FIG. 18B is a plot of density as a function of pressure for
low (23.degree. C.) and high (125.degree. C.) temperatures
according to embodiments herein.
[0025] FIG. 19A is a plot of the optical densities as a function of
pressure for saturation pressure measurements taken at temperatures
ranging from 22.7.degree. C. to 148.7.degree. C. and plotted for
each temperature according to embodiments herein. The temperatures
correspond to the plots on a one to one basis.
[0026] FIG. 19B is a plot of a resulting phase diagram that
includes data obtained with and without thermal nucleation
according to embodiments herein. The temperatures correspond to the
plots on a one to one basis.
[0027] FIG. 20A is a plot of the viscosity for each
depressurization temperature according to embodiments herein. The
temperatures correspond to the plots on a one to one basis.
[0028] FIG. 20B is a plot of the corresponding density of FIG. 19A.
The temperatures correspond to the plots on a one to one basis.
[0029] FIG. 21 is a plot of the corresponding compressibility of
FIG. 19A. The temperatures correspond to the plots on a one to one
basis.
DESCRIPTION
[0030] At the outset, it should be noted that in the development of
any such actual embodiment, numerous implementation-specific
decisions may be made to achieve the developer's specific goals,
such as compliance with system related and business related
constraints, which will vary from one implementation to another.
Moreover, it will be appreciated that such a development effort
might be complex and time consuming but would nevertheless be a
routine undertaking for those of ordinary skill in the art having
the benefit of this disclosure. In addition, the composition
used/disclosed herein can also comprise some components other than
those cited. In the summary and detailed description, each
numerical value should be read once as modified by the term "about"
(unless already expressly so modified), and then read again as not
so modified unless otherwise indicated in context. Also, in the
summary and detailed description, it should be understood that a
concentration range listed or described as being useful, suitable,
or the like, is intended that any concentration within the range,
including the end points, is to be considered as having been
stated. For example, "a range of from 1 to 10" is to be read as
indicating each possible number along the continuum between about 1
and about 10. Thus, even if specific data points within the range,
or even no data points within the range, are explicitly identified
or refer to a few specific points, it is to be understood that
inventors appreciate and understand that any and all data points
within the range are to be considered to have been specified, and
that inventors possessed knowledge of the entire range and all
points within the range.
[0031] The statements made herein merely provide information
related to the present disclosure and may not constitute prior art,
and may describe some embodiments.
[0032] Embodiments disclosed herein provide a means for measuring
the temperature dependence of several fluid properties, including
but not limited to, density, viscosity, and the bubble point. A
pressure-volume-temperature (PVT) apparatus may be deployed in a
downhole tool that could operate in an open or cased hole
environment during a sampling job, but the PVT apparatus may also
have applicability for production logging and surface applications.
For downhole applications, the temperature of the PVT apparatus can
be controlled to bring the sampled fluid to those temperatures that
the fluid would be subjected to during production as the fluid was
transported from reservoir to the surface.
[0033] As illustrated in FIG. 1, a drilling system 300 includes a
bottom hole assembly 302 connected at the bottom end of a drill
string 301 suspended within a wellbore 303. One or more other
downhole tools may be located along the drill string 301 or along a
wireline in the wellbore when the drill string 301 and bottom hole
assembly 302 are removed from the well. Further, in accordance with
one or more embodiments, a PVT device 160 may be contained within a
downhole tool 305 which may be located along the drill string 301,
on a wireline (not shown) or within a downhole tool (not shown).
The PVT device 160 may be electrically connected to a component of
a motor (not shown) or a battery (not shown) to receive energy
therefrom. It should be understood that no limitation is intended
by the arrangement of the drilling system, including the presence
of absence of one or more components. As mentioned above, it is
also envisioned that the drill string 301 may also be replaced by
structures such as a wireline or any other apparatuses to convey
the PVT device 160 into the wellbore, where the PVT device 160 is
electrically connected to one or more tools located on the
wireline.
[0034] Also shown in FIG. 1, near the bottom of the well, the
pressure may be sufficiently high that the fluid is single-phase.
At a given mid-point (the location of which may vary depending on
well properties), the pressure may reach the bubble point when the
fluid breaks phase, producing gaseous and liquid phases. While the
fluid is transiting from the wellbore bottom to the surface, the
temperature is monotonically decreasing, increasing the fluid
viscosity.
[0035] Fluids that may be produced from the formation have their
temperature changed as they are brought to the surface, and hence
experience a dramatic change in the fluid properties, including but
not limited to their viscosity. In order to accurately calculate
the flow rate during production, an accurate knowledge of the
viscosity as a function of depth is useful. Along with temperature
dependence, the fluid pressure may drop below the bubble point
while in transit. System disclosed herein may obtain a fluid sample
from the formation and rapidly vary its temperature in order to
simulate the fluid's passage through the oilwell during the
production stage. In some embodiments, the PVT device 160 may store
a sample extracted from the formation after measurements are
performed. The PVT device 160 may be raised to a shallower depth
and allow the sample within the PVT device 160 to come to
equilibrium, after which additional measurements may be
performed.
[0036] As an example, a description for measuring viscosity will be
discussed, with a comparison of the amount of energy to change the
sample temperature for both mesoscopic and microfluidic approaches.
This would apply as well to a bubble point measurement where one is
interested in the temperature dependence as well. The present
embodiments may be compared to a conventional viscometer that is
macroscopic in size and is directly immersed in the flow-line which
has an inner diameter of approximately 5.5 mm. The total amount of
fluid to fill the conventional sensors and the surrounding region
volume is on the order of 10 milliliters, with an associated heat
capacity of, assuming the specific heat of mineral oil, 1.7
Joules/(gram Kelvin), or a heat capacity of approximately 20
Joules/Kelvin. Hence, 20 Joules of energy are removed to reduce the
temperature by one degree Kelvin. Furthermore, as the sensors are
thermally connected to a large metallic assembly on the order of 1
kilogram (or more), in practice one would reduce the temperature of
this assembly as well. Assuming a specific heat of 0.5 Joules/(gram
Kelvin) for steel, one would have to remove 500 Joules of energy to
reduce the temperature of the whole assembly by one degree. This
approach using conventional technologies will be referred to as
mesoscopic herein.
[0037] As a comparison, microfluidic environments of the present
disclosure may use fluid volumes on the order of ten microliters,
which corresponds to around 10 milligrams of liquid, which has a
heat capacity of about 0.02 Joules/Kelvin (using the above numbers
for the specific heat). In practice, one controls the temperature
of the microfluidic chamber as well, which may have a mass on the
order of 50 grams, and assuming this is fabricated from titanium,
with a specific heat of 0.5 Joules/(gram Kelvin), it would use on
the order of 25 Joules of energy to change the temperature by one
degree. Note that this power usage for the microfluidic approach is
20 times smaller than for mesoscopic approach. Peltier (or
thermoelectric) coolers reveals that models with dimensions with
the proper scale exist and are specified to produce heat fluxes on
the order of 1 Joule/second (1 watt), and one may quickly ramp up
or down the temperature of such a device. Hence, a rapid ramping up
or down of the temperature of a microfluidic-scale of fluidic
volume and associated chamber is feasible.
[0038] FIG. 2 is a flow chart illustrating a process 200 for an
embodiment of sampling fluid into a microfluidic system. A fluid
may be sampled from a formation 201. In some embodiments, a small
volume (on the order of tens of microliters) of fluid will be
sampled, filtered, and passed into a microfluidic system. The
system may be placed into a pressure compensation system where
during the initial phase of its operation, the pressure is
approximately 100 psi lower (or less) than the flowline of the tool
in which it will be implemented. The microfluidic system may
include microfluidic sensors to measure the density, viscosity or
any other physical properties of the fluid. The microfluidic system
may either be located downhole or at the surface. The microfluidic
system may be such as that described in FIG. 3 or FIG. 15.
[0039] The fluid sample may then be introduced into microfluidic
sensors. The pressure and temperature may be controlled precisely
and rapidly so there is minimal thermal mass. The fluid sample may
pass through a fluid path, such as those shown in FIGS. 6-11. The
temperature and pressure controls act on the microfluidic sensors.
The temperature may be controlled precisely and rapidly as there is
minimal thermal mass, pressure may be controlled rapidly as
pressure changes propagate at the speed of sound. For example, the
pressure control may raise or lower the fluid pressure via motion
of the piston thereby reducing or enlarging the volume available to
the fluid. The temperature control can raise or lower the fluid
temperature with a Peltier device or similar device, as well as
raise or lower the temperature of the entire sensor, if desired.
The microfluidic sensors may be used to measure density and
viscosity as the temperature and pressure are controlled and
monitored. The fluid may then be ejected 203 to the borehole. The
measurement may then be repeated.
[0040] For downhole applications, this evaluation may be motivated
by the fact that wellbore temperature changes substantially from
the formation to the surface (FIG. 1). Fluids that are produced
from the formation change their temperature accordingly and hence
experience a dramatic change in their properties, including but not
limited to their viscosity. In order to accurately calculate the
flow rate during production one should accurately know the
viscosity as a function of depth. This is further complicated by
the fact that the fluid may drop below the bubble point while in
transit. Hence, a system may be selected that can obtain a fluid
sample from the formation and rapidly vary its temperature in order
to simulate its passage through the wellbore during the production
stage.
[0041] Generally, embodiments disclosed herein relate to collecting
a fluid from a wellbore, a fracture in a formation, a body of water
or oil or mixture of materials, or other void in a subterranean
formation that is large enough from which to collect a sample. The
fluid may contain solid particles such as sand, salt crystals,
proppant, solid acids, solid or viscous hydrocarbon, viscosity
modifiers, weighing agents, completions residue, or drilling
debris. The fluid may contain water, salt water, hydrocarbons,
drilling mud, emulsions, fracturing fluid, viscosifiers,
surfactants, acids, bases, or dissolved gases such as natural gas,
carbon dioxide, or nitrogen.
[0042] Systems for analyzing these fluids may be located in various
locations or environments, including, but not limited to, tools for
downhole use, permanent downhole installations, or any surface
system that will undergo some combination of elevated pressures,
temperatures, and/or shock and vibration. In some embodiments,
temperatures may be as high as about 175.degree. C. or about
250.degree. C. with pressures as high as about 25,000 psi.
[0043] In general, energy added to a fluid at pressures near the
bubble point to overcome the nucleation barrier associated with
bubble production. Thus, energy may be added to a fluid thermally
through the process of thermal nucleation. The quantity of bubbles
produced at the thermodynamic bubble point via thermal nucleation
is sufficiently small that their presence is detectable near the
place of thermal nucleation in a phase transition cell and not in
other components in the measurement system. However, upon further
depressurization of the system, the supersaturation becomes large
enough that bubble nucleation spontaneously occurs throughout the
measurement system. In one or more embodiments, a fluid sample may
be depressurized at a rate such that bubble detection may occur in
a phase transition cell alone, or may be sufficiently high enough
to be detected throughout the overall system.
[0044] During depressurization of a sample, the density, viscosity,
optical transmission through the phase transition cell, and sample
pressure may be simultaneously measured. Depressurization starts at
a pressure above the saturation pressure and takes place with a
constant change in system volume, a constant change in system
pressure, or discreet pressure changes.
[0045] Collecting and analyzing a small sample with equipment with
a small interior volume allows for precise control and rigorous
observation when the equipment is appropriately tailored for
measurement. At elevated temperatures and pressures, the equipment
may also be configured for effective operation over a wide
temperature range and at high pressures. Selecting a small size for
the equipment is advantageous for rugged operation because the heat
transfer and pressure control dynamics of a smaller volume of fluid
are easier to control then those of large volumes of liquids. That
is, a system with a small exterior volume may be selected for use
in a modular oil field services device for use within a wellbore. A
small total interior volume can also allow cleaning and sample
exchange to occur more quickly than in systems with larger volumes,
larger surface areas, and larger amounts of dead spaces. Cleaning
and sample exchange are processes that may influence the
reliability of the phase transition cell. That is, the smaller
volume uses less fluid for observation, but also can provide
results that are more likely to be accurate.
[0046] The minimum production pressure of the reservoir may be
determined by measuring the saturation pressure of a representative
reservoir fluid sample at the reservoir temperature. In a surface
measurement, the reservoir phase envelope may be obtained by
measuring the saturation pressure (bubble point or dewpoint
pressures) of the sample using a traditional
pressure-volume-temperature (PVT) view cell over a range of
temperatures. Saturation pressure can be either the bubble or
dewpoint of the fluid, depending upon the fluid type. At each
temperature, the pressure of a reservoir sample is lowered while
the sample is agitated with a mixer. This is done in a view cell
until bubbles or condensate droplets are optically observed and is
known as a Constant Composition Expansion (CCE). The PVT view cell
volume is on the order of tens to hundreds of milliliters, thus
using a large volume of reservoir sample to be collected for
analysis. This sample can be consumed or altered during PVT
measurements. A similar volume may be used for each additional
measurement, such as density and viscosity, in a surface
laboratory. Thus, the small volume of fluid used by microfluidic
sensors of the present disclosure (approximately 1 milliliter total
for measurements described herein) to make measurements may be
highly advantageous.
[0047] In one or more embodiments, an optical phase transition cell
may be included in a microfluidic PVT tool. It may be positioned in
the fluid path line to subject the fluid to optical interrogation
to determine the phase change properties and its optical
properties. U.S. patent application Ser. No. 13/403,989, filed on
Feb. 24, 2012 and United States Patent Application Publication
Number 2010/0265492, published on Oct. 21, 2010 describe
embodiments of a phase transition cell and its operation. Both of
these applications are incorporated by reference herein. The
pressure-volume-temperature phase transition cell may contain as
little as 300 .mu.l of fluid. The phase transition cell detects the
dew point or bubble point phase change to identify the saturation
pressure while simultaneously nucleating the minority phase.
[0048] The phase transition cell may provide thermal nucleation
which facilitates an accurate saturation pressure measurement with
a rapid depressurization rate of from about 10 to about 200
psi/second. As such, a saturation pressure measurement (including
depressurization from reservoir pressure to saturation pressure)
may take place in less than 10 minutes, as compared to the
saturation pressure measurement via standard techniques in a
surface laboratory, wherein the same measurement may take several
hours.
[0049] Some embodiments may include a view cell to measure the
reservoir asphaltene onset pressure (AOP) as well as the saturation
pressures. Hence, the phase transition cell becomes a configuration
to facilitate the measurement of many types of phase transitions
during a CCE.
[0050] In one or more embodiments, a densitometer, a viscometer, a
pressure gauge and/or a method to control the sample pressure with
a phase transition cell may be integrated so that most sensors and
control elements operate simultaneously to fully characterize a
live fluid's saturation pressure. In some embodiments, each
individual sensor itself has an internal volume of no more than 20
microliters (approximately 2 drops of liquid) and by connecting
each in series, the total volume (500 microliters) to charge the
system with live oil before each measurement may be minimized. In
some embodiments, the fluid has a total fluid volume of about 1.0
mL or less. In other embodiments, the fluid has a total fluid
volume of about 0.5 mL or less.
[0051] This configuration is substantially different than a
traditional Pressure-Volume-Temperature (PVT) apparatus, but
provides similar information while reducing the amount of fluid
consumed for measurement. FIG. 3 is a schematic of one embodiment
of a PVT apparatus for use downhole. In some embodiments, the PVT
apparatus may be included into another measurement tool or may be
standalone on a drill string or wire line. Although FIG. 3 includes
a phase transition cell 140 for saturation pressure detection with
optical measurements, a microfluidic vibrating tube densitometer
141 for density measurements, and a microfluidic vibrating wire
viscometer 142 for viscosity measurements, some embodiments may
include density or viscosity sensors to measure fluid properties as
the cell depressurizes or pressurizes, while other embodiments may
benefit from the phase transition cell working with no additional
sensors at all. Compressibility measurements may also occur in some
embodiments. The compressibility may be measured from the
derivative of volume with respect to pressure with knowledge of the
system 160 volume.
[0052] The control of the pressure within the system may use a
pressure control device 143 or an alternate pressure control
device, such as one based on a sapphire piston. In such an
embodiment, the control of the pressure in the system may be
adjusted by moving the piston to change the volume inside the
piston housing 145 (partially shown) and, thus, the sample volume.
The system's small dead volume (less than 0.5 mL) facilitates
pressure control and sample exchange. In some embodiments, the
depressurization or pressurization rate of the fluid is less than
200 psi/second. In some embodiments, the fluid is circulated
through the system at a volumetric rate of no more than 1 ml/sec.
Teflon, alumina, ceramic, zirconia or metal with seals may be
selected for some components for various embodiments of the
pressure control device. Smooth hard surfaces may be used to
minimize friction of the moving piston and both energized and
dynamic seals may be used.
[0053] The sample fluid is in pressure communication with the
pressure gauge 144. The pressure gauge 144 can measure small
pressure changes such as 2 to 3 psig. The gauge utilizes small
sample volume for its external housing and also has low dead volume
of less than about 1 mL. Some embodiments may have a dead volume of
less than 0.5 mL or less than 0.05 mL.
[0054] The phase transition cell 140 includes a 2 mm long flowline
constrained by two sapphire windows or lenses, United States Patent
Application Publication Number 2010/0265492 provides additional
details and is incorporated by reference herein. Light in the
optical path between the two windows or lenses is highly sensitive
to the presence of fluid interfaces, such as that associated with
bubbles in a liquid (produced at bubble point) or liquid droplets
in a gas (produced at dew point). An 80 percent Nickel, 20 percent
Chromium (NICHROME80.TM.) wire of diameter 100 microns or less is
installed orthogonal to the flow path in the phase transition cell
to thermally agitate the fluid to overcome the nucleation barrier,
Some embodiments may use a wire comprising platinum, tungsten,
iridium or a platinum-iridium alloy. A high current pulse (c.a. 5
amperes) of duration 5 microseconds quickly heats the fluid
surrounding the wire by about 25.degree. C. As the heat dissipates
(in about 0.1 s) and the local temperature returns to that of the
system, the bubbles formed in a liquid sample either collapse or
remain stable, according to whether the system is above the
saturation pressure or, inside the two-phase region, respectively.
The mechanisms of the nucleation process and its operability on
both sides of the cricondenbar are described in U.S. patent
application Ser. No. 13/403,989, filed on Feb. 24, 2012 and U.S.
patent application Ser. No. 13/800,896, filed on Mar. 13, 2013.
Both of these references are incorporated by reference herein in
their entireties.
[0055] As mentioned above, the tool of the present disclosure may
include a densitometer 141 to measure fluid density which may be
used to calculate compressibility. The fluid compressibility, k,
can be calculated by precisely measuring the fluid density while
varying the pressure. The compressibility can be defined as the
relative change in fluid density with the change in pressure as in
the following equation:
k [ .rho. ] = 1 .rho. .differential. .rho. .differential. P ( 1 )
##EQU00001##
[0056] In practice, the noise introduced by taking a derivative can
be minimized by first smoothing and then fitting a local second
order polynomial to the reciprocal of the density data. Due to the
curvature of the data with pressure, the fit is more accurate when
applied to the reciprocal of the density as compared to the fit
directly on the density itself. For each pressure, the subset of
the density data includes 31 densities that are centered on the
pressure of interest. In theory, this corresponds to a pressure
range of thousands of psi, but in practice this range covers a few
hundred psi. The local fit can then be described as fitting the
inverse density to a second order polynomial:
1 .rho. [ P ] = A + BP + CP 2 ( 2 ) ##EQU00002##
[0057] Determination of the local coefficients A,B,C, allows one to
analytically calculate their derivative and then plug into the
above compressibility equation as
k [ P ] = - ( B + 2 CP ) A + BP + CP 2 = .rho. [ P ] ( B + 2 CP ) (
3 ) ##EQU00003##
[0058] In practice, this smoothes the compressibility measurement
while not introducing a strong bias. It has the further advantage
of being model-independent, thereby being applicable regardless of
the fluid's proximity to the critical point.
[0059] FIG. 3 provides a schematic view of one embodiment of the
phase transition cell in combination with other elements. The
components may be configured to work together or individually to
observe a fluid sample. The devices present in the figure may be
used in one system. They may be used individually in one system or
a combination of some of them may be used. Each of the individual
components may be in contact with the control system (not shown).
The control system is in contact with the components and with an
operator who is using a computer at the surface of the formation or
Other location. The control system is electronic and may control
the mechanics of the components. Throughout the elements, several
temperature sensors may be embedded in devices or tubing
connections to observe the temperature of the fluid.
[0060] In one embodiment, the fluid is collected through a membrane
146 as described in U.S. Pat. No. 7,575,681, issued on Aug. 18,
2009, and U.S. Pat. No. 8,262,909, issued on Sep. 11, 2012. Both of
these references are incorporated by reference herein. The membrane
146 is housed in a frame configured for supporting the membrane
even during exposure to harsh environments and for cleaning
activities including backflush backflushing to remove particulate
buildup from the membrane. In some embodiments, the membrane 146
prevents particles with a dimension of 10 micron or greater to flow
through the membrane. In some embodiments, the membrane is
hydrophobic. As pictured, the fluid is flowed through the membrane
146 as in a cross-flow. In some embodiments, fluid is flowed across
the membrane as in dead-end filtration.
[0061] Next, the fluid collects behind the membrane 146 and flows
through tubing on to an entry valve 147. The entry valve 147 is a
needle valve or ball valve or other valve that is selected for its
volume and fluid flow properties. The entry valve 147 features a
small dead volume and precise open and close control. The entry
valve 147 is controlled to allow or prevent a specific fluid flow
to the phase transition cell and/or to allow backflushing of the
membrane 146. The valve 147 may be closed completely in some
operations. It is selected to be modular and low cost for
maintenance and repair.
[0062] Then, the fluid flows through the phase transition cell 140
as described above. From the phase transition cell, fluid flows
through a densitometer 141. The small volume of the fluid flowing
through the densitometer 141 utilizes a carefully selected cross
sectional area and fluid flow path. The risk of deposition and/or
flocculation of asphaltenes and other highly viscous or readily
precipitating material also influences the design. One example of
such a densitometer is described in U.S. Patent Publication No.
2010/0268469 published on Oct. 21, 2010, which is incorporated by
reference, in its entirety, herein.
[0063] Then, the fluid flows through a viscometer 142. Like the
densitometer 141, the viscometer 142 contains a small volume of
fluid and utilizes a carefully selected cross sectional area and
fluid flow path. A similar risk of surface contamination exists and
thoughtful design elements and considerations are considered. One
example of such a viscometer is described in U.S. patent
application Ser. No. 13/353,339, filed on Jan. 19, 2012, which is
incorporated by reference, in its entirety, herein.
[0064] The fluid enters the pressure control device 143 such as a
sapphire based piston and then exerts a pressure on the pressure
gauge 144. The pressure gauge can measure small pressure changes
with a precision better than 0.1 psi and an accuracy of 2 to 3 psig
under downhole conditions. The gauge has low volume for its
external housing and also has low dead volume of about 0.5 mL or
less.
[0065] Next, the fluid flows on to an exit valve 148. Like the
entry valve 147, the exit valve 148 is a needle valve or other
valve that is selected for its volume and fluid flow properties.
The exit valve 148 features a small dead volume and precise
control. The exit valve 148 is controlled to allow or prevent a
specific fluid flow to a back pressure regulator 149. In some
embodiments, a back pressure regulator is not included. The valve
148 may be closed completely in some operations. It is selected to
be modular and low cost for maintenance and repair. Some
embodiments may include a bypass flow line 151 with a pressure
gauge 152 and pressure control device 153. The fluid may be sent
downhole through flow line 150. Embodiments could be implemented
without a back pressure regulator and simply use the differential
pressure created by the piston to induce fluid to flow into the
microfluidic system through the membrane 146 in a dead-end
filtration configuration.
[0066] In another embodiment, the membrane 146 is a cross-flow
configuration. The piston pumps fluid through the membrane 146, the
entry valve 147, and the exit valve 148. The valve configuration
for pumping into the system is the entry valve 147 open and exit
valve 148 closed, and the configuration for pumping out of the
system (discharging used fluid) is the entry valve closed 147 and
the exit valve open 148.
[0067] Some embodiments may have a phase transition cell, piston,
and pressure gauge that have a combined external volume 154. This
external volume 154 may be about 10 liters or less. The external
volume 154 may be about 2.5 gallons or less. The external volume
154 may be configured to fit into a wellbore, a downhole oilfield
tool or a formation evaluation tester.
[0068] System performance may depend on the arrangement of sensors
in the flow path. Fluid becomes progressively more contaminated the
further downstream from the sample inlet a sensor is, due to
limitations of flushability of the fluidic connectors, sensors, and
components. Therefore, the sensors that may be most sensitive to
contamination or have the highest levels of accuracy should be put
as near the inlet as possible. In the configuration shown in FIG.
3, the bubble point measurement is both sensitive to contamination
and has high accuracy, so it is placed first. The densitometer is
placed second, as this is a relatively high precision measurement
but has lower sensitivity to contamination than the bubble point.
The viscometer is located third, as the desired precision is low
compared to either the densitometer or bubble point. The pressure
gauge and piston which may be insensitive to contamination can be
placed last. The arrangement of the sensors in FIG. 3 is one of
many embodiments which can be implemented.
[0069] Some embodiments may have the apparatus including the phase
transition cell 140, piston 143, and pressure gauge 144 that have a
combined external volume. This external volume may be about 10
liters or less. The external volume may be about 2.5 gallons or
less. The external volume may be configured to fit into a
wellbore.
[0070] In some embodiments, the components (such as the phase
transition cell 140, viscometer 143 and densitometer 144) may be
connected by a device, such as a microfluidic union (shown in FIG.
4 in greater detail), that allows a hydraulic connection to be made
between two metal tubes of such small inner diameter, of order 1
millimeter or less, that they could be described as capillaries,
while maintaining electrical isolation between the two metal tubes.
The microfluidic union may be described as an electrically
isolating hydraulic connector. The device prevents random
electrical noise, ever present in metal tubes connected to an
electrically enabled instrument, to bias or prevent suitable
operation of microsensors connected to this tubing. In particular,
a microfluidic densitometer 144 or a microfluidic coriolis force
meter (to measure mass flow rate, not shown) may benefit from this
device. The device operates over a wide range of temperature (up to
about 200.degree. C.) and pressure (about 30,000 psi) while adding
a negligible amount of dead or non-flushed volume and acts as a
hydraulic union. The device is operable under a large amount of
shock and vibration, as often encountered with logging while
drilling (LWD) tools.
[0071] FIG. 4 is a sectional view of microfluidic junction 800.
Junction 800 includes an o-ring 803, a backup ring 805, a metal
flange 804 (which may be welded or brazed to tubing 801), and an
electrically isolating backup ring 806 to connect first tubing 801
and second tubing 810. The tubing 801 may have a diameter 802 of 1
mm. The tubing 801 may be made of stainless steel, Hastelloy,
medical grade tubing, etc. Tubing 801 may have a terminal end
adjacent o-ring 803. Behind o-ring 803 are backup ring 805, metal
flange 804 and electrically isolating backup ring 806 through which
tubing 801 also extends. The backup ring 805 and isolating backup
rings 806 may be made of PEEK, other polymers, ceramics, composite
materials, etc. Some embodiments may use a flange 804 comprising
steel, polymer, or other material. Some embodiments may also
comprise a gland 807 and electrically isolating sleeve 808 through
which tubing 801 also extends. The terminal end of tubing 801 (and
o-ring 803, backup ring 805, metal flange 804, isolating backup
ring 806 and gland 807) may be received by a union 809, also
retained as a support device. Electrically isolated from the tubing
801, but in hydraulic connection is tubing 810. While tubing 810
may be a second tubing as described above, it is also within the
scope of the present disclosure that tubing 810 may be in hydraulic
connection with but electrically isolated from a third tubing using
a junction similar to that illustrated in FIG. 4. The components
support device or union 809 to connect a second capillary tube by
laser welding or metal seal or other means.
[0072] The device of FIG. 4 functions to fluidically and
hydraulically connect two metal tubes (801 and 810) while
maintaining electrical isolation. A flange 804 may be welded or
brazed onto the tube 801. An o-ring 803 and backup ring 805 may be
stacked onto the tube 801. On the other side of the flange 804, an
electrically isolating ring 806, made of a plastic or ceramic or
other electrically insulating material or components, may be
installed by sliding down the tube. Next, an electrically isolating
sleeve 808 may be slid in place, and finally a gland 807. The gland
807 backs the stack of components under application of internal
pressure. By proper choice of the dimensions of the flange 804 and
the block 809 that the gland 807 screws into, the tubes 801 and 810
are electrically isolated from one another. While not explicitly
shown, the tube 810 may be brazed or welded hydraulically to make a
pressure tight seal to 809. "Gland" herein means a type of nut but
with the threads on the outside instead of the inside and with a
hole in the center (see FIG. 4). This type of geometry where one
tube is inserted into a block or pressure housing is referred to as
a "stabber" connection in oilfield parlance, as is often the case,
sealing is achieved by a combination of an o-ring and backup ring.
Stabbers do not generally create electrical isolation, but by
careful choice of the flange dimensions and associated components
electrical connectivity can be removed. A similar seal is made here
(FIG. 4). The second capillary tube attached to the union may be
sealed to the union by conventional means of a metal seal, a welded
seal, or one of several other methods (see FIG. 4).
[0073] In some embodiments, an electrically isolating ring 806,
comprising one of many electrically isolating materials, including
but not limited to plastic such as poly ether ketone, mica,
ceramics including silicon nitride or aluminum oxide, may be placed
under compression to electrically isolate the gland from the
flange. In some embodiments, the Outer Diameter (OD) 802 of the
flange may be slightly smaller than that of the housing 804. A thin
PEEK sleeve 808 may be placed between the capillary tube 801 and
the gland 807. The gland 807 may be optional if the tubing 801 is
sufficiently rigid to withstand a compressive force pushing on the
other end of the first capillary tube 801 to "stab" it into the
microfluidic union.
[0074] FIG. 5 is a view of a vibrating tube densitometer 1000 with
integrated isolation components 1001. A thin tube is the vibrating
element 1002 of the vibrating tube densitometer 1000.
[0075] Some embodiments feature implementation of microfluidic
sensors in an actual downhole tool in different ways, including a
modular `plug and play` system which allows sensors to be easily
replaced, moved, and exchanged with each other, as shown in FIG. 6.
In such an implementation, the sample may flow from one sensor to
the next, traveling through channels which connect the different
sensing modules. The connections discussed herein (and shown in
FIGS. 4, 9 and 10) serve as the basis for a system that operates at
high pressure and high temperature (HPHT), high shock and vibration
conditions downhole and/or on the surface.
[0076] As shown in FIG. 6, some embodiments provide multiple
flowlines 1100, 1101 of the tools running through a sensor platform
1102 not as a single piece of tubing, but rather as a series of
connections that connect different modular sensing components.
Different sensing `blocks` could be stacked in various
configurations, tailored for the specifications of the system. FIG.
6 illustrates attaching together interchangeable sensor blocks
1103, 1104, 1105, 1106, 1107.
[0077] Each of these sensor `blocks` may house multiple sensors and
may operate as a stand-alone modular system. To make connections
between these smaller systems or within each of these smaller
systems, different low dead-volume connections 1108 may be
selected.
[0078] Products able to operate at HPHT, under high shock and
vibration conditions are commercially available from companies such
as High Pressure Equipment.TM. and Swagelok.TM. These connections
1108 are metal-metal seals. The high pressure of a fluid is held
inside the connection by the formation of a seal between a metal
tube and a metal fitting. Torque applied to a gland holds this
metal-metal seal in place. Generally, these metal pieces can be
reused for a limited number of times before being replaced. In some
embodiments, a polymeric o-ring may be utilized to form the seal
which retains high pressure fluid. Force from clamping together the
two parts being fluidically connected keeps the o-ring in place.
The use of a polymer o-ring as the pressure retaining seal
decreases the likelihood that a seal will fail after repeated use.
An o-ring can be easily replaced, whereas replacing a metal seal
could involve replacement/resizing of metal tubing as well as the
metal fitting.
[0079] There are many configuration options for a modular `plug and
play` system for microfluidic components operating in downhole
conditions. Such a system allows various sensors to be replaced
without disturbing other sensors in the platform, easing the
exchange of sensor functionally and replacement of faulty sensors.
This module operates in series with other downhole non-microfluidic
or microfluidic sensing blocks or as a stand-alone unit.
[0080] As shown in FIGS. 7a and 7b, in one arrangement, the fluid
flows into a given sensor 1200 in one direction and flows out of
the sensor in a different direction. The exit flow could be in any
direction including, but not limited to, 180 degrees from the
entrance flow. The entrance ports 1201 and exit ports 1202 of
various sensors could attach to a common `breadboard` chassis 1203.
This breadboard 1203 features internal fluidic paths 1204 to route
sample from one sensor to the next. The connections for the sensors
could be located on both sides of the breadboard (FIG. 7a) or one
side (FIG. 7b). If on one side, the breadboard would feature
internal fluidic channels that, like the sensors, allow fluid to
flow in one direction and out in a different direction. If on both
sides, straight channels through the breadboard allow fluid to flow
one sensor to the next. In other embodiments, the channels may not
be straight.
[0081] This breadboard is a chassis for the larger tool that the
microfluidic components fit into, or it is a stand-alone unit. In
either embodiment, fluidic connections not made by a sensor or the
breadboard are done with a microfluidic `jumper`. This jumper would
serve as a simple fluidic connection to enable the sample to flow
from one sensor to the next sensor or the breadboard.
[0082] Sensors are securely attached to the breadboard, locking
them into place and forming the seal with the connectors to keep
the sample inside the microfluidic path. This arrangement--one
where the connectors are inserted into a common fluidic
breadboard--allows a sensor to be moved and replaced without
disturbing other sensors already installed in the system.
[0083] As shown in FIG. 8, in a `direct connect` arrangement, the
fluid either flows in and out of a sensor (or jumper) in the same
direction or passes through from one end to the other. `Direct
connect` allows sensors to be replaced and exchanged. Sensors 1301,
1302, 1303 may be directly connected to one another--fluid would
pass from one sensor or jumper to the next, without traveling
through a breadboard. Sensors 1301, 1302, 1303 could be arranged in
any order. This configuration would offer lower overall system
volume then the `plug and play` arrangement, but not the ease of
replacing a sensor without disturbing the other sensors in the
system.
[0084] A microfluidic `plug and play` system for downhole use (i.e.
HPHT, shock and vibration conditions) depends on the use of a
microfluidic connection that allows components to be easily removed
and replaced by other components. Such a connector, described below
and shown in FIGS. 9A and 9B, has been developed and is suitable
for downhole use.
[0085] The apparatus disclosed is a metal tube that has been cut to
a specific length and machined to have at least three outer grooves
running around the outer diameter. In some embodiments, more or
less grooves may be used. O-rings rest in outer two of these
grooves, and are retained in place with a metal `lips` at the end
of piece. This piece is a connector 1401 which allows fluid to flow
from one device to another: the inner diameter 1402 of the
connector may be hundreds of microns in diameter. Each device
(bread board and/or sensor and/or jumper) features receiving holes
1403 for the connector which connect to a fluidic path 1404 that
allows fluid to be transported through the device.
[0086] As shown in FIGS. 10a and 10b, polymeric o-rings 1501, 1502,
1503, and 1504 serve as the sealing mechanism to retain high
pressure fluid inside the connectors. There are numerous
configurations of o-rings that may be selected. FIGS. 10A and 10B
provide two different configurations. In one, two polymeric
(Viton.TM.) o-rings 1501 and one PEEK o-ring 1502 are placed in
grooves, and in the other one Viton.TM. o-ring 1503 and one PEEK
o-ring 1504 are used. These are two examples of o-ring
configurations and materials and there are more possibilities.
[0087] In the final system assembly, one connector 1401 is inserted
into two receiving holes: these receiving holes could be in
sensors, the breadboard or microfluidic jumpers. The receiving
holes and connectors are designed to minimize the amount of
`dead-volume` fluid of the connection. The dead volume is the
amount of fluid that exists at the connector/hole interface but not
inside the flow channel of the connector. For example, the
connector embodiment shown in FIGS. 10A and 10B with one Viton.TM.
o-ring at each end, the fluidic dead volume (fluid not inside the
connector) is 0.0006422 mL.
[0088] To facilitate the placement of a connector 1605 into a
receiving hole 1604, alignment pins and holes, such as those shown
in FIG. 11, can be used. These pins 1601 and holes 1602 help to
guide the connector 1605 into the receiving hole 1604, preventing
bending of the connector. An external alignment system, which may
include guiding rails that can be removed once the fluidic
connection is in place, can also be used, in addition or in
combination with the alignment pins and holes.
[0089] Both the connectors shown in FIGS. 10A and 10B have been
shown to hold high pressure at elevated temperature. Both types of
connectors may be placed in an oven at 150.degree. C., while the
internal pressure of the sample inside raised and lowered in
increasingly large steps. Ultimately, both configurations held
20,000 psi of pressure at 150.degree. C. Test conditions are shown
in FIG. 12.
[0090] Pressure retention while undergoing shock and vibration is
also a design consideration. A connector with two Viton.TM. o-rings
and one PEEK o-ring (as seen in FIG. 10) has also been shown to
hold 20,000 psi of pressure while undergoing 100,000 shocks at 500
G (at room temperature). Table 1 summarizes the number of shocks
and shock levels applied to the connectors. X and Y-axis refer to
the orientation of the connectors with respect to the moving arm of
the shock machine. In the orientations test the fluidic path of the
connector was perpendicular to the arm of the shock machine: the X
and Y-axis results of this test are interchangeable, since the
connector is rotationally symmetric about its fluidic path.
TABLE-US-00001 TABLE 1 Number Fluid Pressure Axis of Shocks Shock
Level Inside Connector X 3,000 500 G 20,000 psi Y 97,000 500 G
20,000 psi
[0091] The HPHT, shock and vibration resistant connectors described
above can be integrated into modular microfluidic systems, as shown
in FIGS. 13A, 13B, and 13C. In FIG. 13A, connectors 1704 allow
fluid to move from the breadboard 1702 to sensors 1701 via fluidic
paths 1703. The fluid path in the jumpers 1706 and the breadboard
1705 also enable fluid to move between sensors. Alignment pins 1707
help facilitate sensor installation. Alignment pins 1711 are also
found in the one-sided chassis scheme shown in FIG. 13B. Fluid
moves to and from sensor 1708 via connectors 1710 and fluid paths
1712 and 1709. 1712 is the fluid path internal to the chassis 1713.
In the `direct connect` configuration shown in FIG. 13C, sensors
1750 are fluidically connected via connectors 1753 and fluid paths
1751. Alignment pins 1752 can be used. Here, the function and
placement of the connectors in the modular system is illustrated.
When utilized as shown, these connectors enable low dead-volume
`plug and play` and `direct connect` microfluidic apparatuses. The
use of different connectors, such as metal-metal seals, would
increase the volume of the system: additional tubing length between
the sensors would have to be incorporated to leave physical access
to the connectors.
[0092] In some embodiments, the connectors have a total internal
volume of less than 1 mL. Some embodiments utilize connectors that
form a fluid connection that survives a pressure of about 15,000
psi or more. Some embodiments include connectors that form a fluid
connection that operates at a temperature of about 175.degree. C.
Some embodiments use connectors that include tubing. Sometimes, the
tubing has an internal diameter of about 1.0 mm or less. Some
embodiments benefit from tubing that has an internal diameter of
0.25 mm or less.
[0093] In some embodiments, the measurement of the fluid properties
at the temperature and pressure of the formation alone does not
suffice to predict the behavior of reservoir fluids because the
temperature will change dramatically as it is pumped from the
formation to the surface. Correlations are often inadequate as
predictive indicators of such behavior. In some embodiments, the
thermal mass of a small volume allows the temperature to be rapidly
and accurately controlled such that the transport properties,
including density and viscosity, can be then be measured as a
function of temperature in a matter of minutes. This, when combined
with a means of controlling the pressure of the sample, allows one
to characterize the properties of the live fluid so that its
behavior is understood in a predictive manner during its transit
from the formation to the surface.
[0094] FIG. 14 is a Peltier cooler 1900 designated with the cool
side towards a microfluidic sensor 1901 and the hot side (the side
by which the Peltier cooler radiates heat so as to effectively cool
the cold side) towards the tool housing. Referring to FIG. 14, the
live downhole fluid will be introduced through the two microfluidic
connections 1902a and 1902b on the top and the two upper valves
1903a and 1903b closed. Several measurements, of which viscosity,
density, or bubble point could be one, will be made with the
microfluidic sensors 1901. At this point, the system allows an
operator to vary the pressure with the pressure compensation system
1904 and the temperature with the Peltier device 1905 while
maintaining the same fluid sample in the microfluidic channels. If
the pressure and temperature dependence of the well is known as a
function of depth, an identical set of temperature-pressure points
may be created in the microfluidic device so as to interrogate the
fluid properties in a way that mimicked the fluid's transit to the
surface.
[0095] As a further elaboration, after dropping the pressure below
the bubble point one could separate the gaseous phase from the
liquid phase so that a viscosity measurement could be exclusively
performed on the liquid portion. By designing the microfluidic
channels to be oil wet, a continuous oil stream could be siphoned
off. The viscosity of this liquid stream is then measured. The
viscosity measurement is then combined with temperature control to
provide the viscosity of the liquid portion of the live fluid when
the pressure is dropped below the bubble point.
[0096] Further details of using the PVT apparatus in conjunction
with a wellbore tool and methods for implementing the PVT apparatus
are described in U.S. patent application Ser. No. 13/829,710,
entitled "Method to Perform Rapid Formation Fluid Analysis" and
filed on Mar. 14, 2013.
EXPERIMENTAL RESULTS
[0097] A PVT apparatus as shown in FIG. 15 was used to investigate
a multi-alkane sample as listed in Table 2.
TABLE-US-00002 TABLE 2 Component Mole percentage Methane 47 Ethane
24 n-Pentane 14 n-Hexane 10 n-Heptane 5
[0098] FIG. 15 is a schematic of a PVT apparatus 100. The
components in the region indicated by dashed line 101 may be in a
temperature-controlled oven or in a downhole oilfield tool. Within
the oven 101, the PVT apparatus 100 may include a filter 105,
valves 103 and 104 to isolate the sample, a phase transition cell
106, a densitometer 107, a viscometer 108, a pressure gauge 109,
and a floating piston 114. Outside the oven 101, the PVT apparatus
100 may include a pressure gauge 110, a Single Phase Sample Bottle
(SSB) 111, and at least two valves 112 to direct pressure control
from a pump 113 between the SSB 111 and the floating piston
114.
[0099] The PVT apparatus 100 includes a single phase sample bottle
(SSB) 111. The SSB 111 may be of the type produced by
Schlumberger-Oilphase, Aberdeen. A pump 113 may be used to
pressurize the SSB 111. The pump 113 may be an Isco 65D syringe
pump filled with water (Teledyne Isco). The SSB 111 may include a
floating piston 114 for maintaining pressure on the sample while
providing fluidic isolation from the source of the pressure, i.e.,
pump 113.
[0100] A live fluid was stored in the Single-Phase Sample Bottle
111. The SSB 111 may be one such as that manufactured by
Schlumberger-Oilphase, Aberdeen. The SSB 111 was pressurized with
an pump 113 filled with water. The pump 113 may be an Isco 65D
syringe pump (Teledyne Isco). The SSB 111 includes a floating
piston 114 for maintaining pressure on the sample while providing
fluidic isolation from the source of pressure, which in this case
was water pressurized by pump 113. Tubing of Outer Diameter (OD)
1/16'' and Inner Diameter (ID) 0.020'' was used wherever possible
in the experimental apparatus as a standard so as to reduce the
system volume. A pressure gauge 109 with a customized low
dead-volume fitting (7 microliters) was employed inside of the oven
to measure the pressure of the sample during depressurization. The
pressure gauge 109 may be a Kistler pressure gauge. Calibration of
the pressure gauge 109 was performed against a pressure gauge 110
(outside oven at ambient temperature) of higher accuracy at each
temperature before and after each experiment since the calibration
was found to drift substantially upon a change in the temperature.
The pressure gauge 110 may be a Quartzdyne pressure gauge.
[0101] The PVT system may initially be charged with a fluid such as
hydraulic oil or an alkane mixture at ambient pressure and then
pressurized with fluid hydraulically connected to the waste SSB.
During an experiment the live oil was charged into the PVT system
from the sample cylinder and discharged afterwards into a waste
cylinder (which may be a SSB), thereby maintaining the sample
pressure far above the saturation pressure so as not to break
phase. Both cylinders were stored at ambient temperature outside of
the oven, but the sample fluid was quickly heated to the oven
temperature due to its low thermal mass (about 300 microliters
charged into the system per measurement). A new aliquot of live oil
was charged into the system for each depressurization experiment.
The valves 112 on the two cylinders were closed after charging the
system and the sample was isolated between valves 103 and 104. The
valves 103 and 104 may be AF1 needle valves (High Pressure
Equipment Company, HIP) which were located inside of the oven (FIG.
15), thereby maintaining the sample at uniform temperature. The MS
series microreactor 115 from HIP may be used to controllably
depressurize the isolated sample. The microreactor 115 includes a
small floating piston 114 where pressure was controlled with an
Isco pump. The microreactor 115 was hydraulically similar to the
sample cylinder but may have a maximum volume of about 10 mL.
[0102] The fluid may be collected in the SSB 111 and flow through
tubing via an entry valve 112a. The entry valve 112a may be a
needle valve or other valve that is selected for its volume and
fluid flow properties. The entry valve 112a features a small dead
volume and precise open and close control. The entry valve 112a may
be controlled to allow or to prevent a specific fluid flow to the
phase transition cell and/or to allow backflushing of the filter
105. The valve 112a may be closed completely in some operations.
The valve 112a may be selected to be modular and low cost for
maintenance and repair.
[0103] Next, the fluid collects behind the filter 105 and flows
through tubing to an entry valve 103. The entry valve 103 may be a
needle valve, ball valve or other valve that is selected for its
volume and fluid flow properties. The entry valve 103 features a
small dead volume and precise opening and closing control. The
entry valve 103 is controlled to allow or prevent a specific fluid
flow to the phase transition cell and/or to allow backflushing of
the filter 105. The valve 103 may be closed completely in some
operations. The entry valve 103 may be selected to be modular and
low cost for maintenance and repair. The valves 103 and 104 are
configured such that the pressure experienced by both the pressure
gauge 110 (outside oven) and pressure gauge 107 (inside oven) could
be uniformly varied from about 1000 to about 8000 psi, thereby
performing an in-situ calibration of the pressure gauge 107 at the
temperature of the oven, with or without the use of the
micropiston.
[0104] The PVT apparatus 100 may include a first valve (V1) 103 and
a second valve (V2) 104. Valves 103 and 104 may be located in the
oven with their valve handles situated outside such that they could
be operated without opening the oven door and altering the
temperature. In other embodiments, they may be controlled by a
motor and associated electronics such that operation may be
effected remotely. In some embodiments, the first valve 103 and
second valve 104 may be AF1 valves (High Pressure Equipment
Company, HIP). In other embodiments, the first valve 103 and second
valve 104 may be a needle valve, ball valve or other valve that is
selected for its volume and fluid flow properties. The first valve
103 and second valve 104 may feature a small dead volume and
precise open and close control. The first valve 103 and second
valve 104 may controlled to allow or prevent a specific fluid flow
to the phase transition cell 106 and/or to allow backflushing of
the filter 105. The first valve 103 and second valve 104 may be
closed completely in some operations. The first valve 103 and
second valve 104 may be selected to be modular and low cost for
maintenance and repair.
[0105] The control of the pressure within the apparatus 100 may use
a pressure control device such as a sapphire based piston 114. The
control of the pressure in the apparatus 100 is adjusted by moving
the piston 114 to change the volume within the piston housing and,
thus, the sample volume. The apparatus' 100 small dead volume (less
than 0.5 mL) facilitates pressure control and sample exchange. In
some embodiments, the depressurization or pressurization rate of
the fluid may be less than about 200 psi/second. In some
embodiments, the fluid may be circulated through the apparatus 100
at a volumetric rate of no more than 1 ml/sec. Teflon, sapphire,
alumina, ceramic, zirconia, or metal with seals may be selected for
some components for various embodiments of the pressure control
device. Within the piston 114, smooth hard surfaces may be used to
minimize friction of the moving piston and both energized and
dynamic seals may be used.
[0106] The densitometer 109 and viscometer 108 are configured for
use in the system. The vibrating tube densitometer 109 measures the
resonant frequency of a thin-walled tube of volume 20 microliters
driven to oscillate using the Lorentz force. By prior calibration
over the relevant pressure and temperature range the density of the
fluid that is circulated through the tube may be deduced. In
principal, the fractional frequency shift experienced by the
resonator is not scale dependent meaning that the measurement
volume can be even further reduced, though the resonance amplitude
would be reduced as the cross-sectional area of the tube's path is
reduced. For viscosity measurements, the vibrating wire viscometer
108 operates by measuring the decrement (inverse of twice the
quality factor) of a resonating wire immersed in the fluid.
Interpretation is provided by using the methods described in
Retsina, Richardson, Waketam, "The theory of a vibrating rod
viscometer," Applied Scientific Research, 43:325-46 (1987), which
is incorporated by reference herein. These sensors perform with a
volume of no more than 20 microliters and operate at elevated
temperature and pressure.
[0107] In order to benchmark the measurement of saturation pressure
with this system, synthetically prepared live fluids were created
by starting with known quantities of liquid n-alkanes (for example
n-pentane, n-hexane, and n-heptane) determined gravimetrically. The
alkanes were placed in a sample bottle of known volume and
pressurized to approximately 1800 psi with partial pressures of
methane and ethane. The two-phase sample was isolated with a valve,
pressurized to 10,000 psi, and rocked overnight so as to completely
dissolve the methane and ethane into the liquid phase. This
produced a sample of known composition, but with unknown saturation
properties (Table 2). Based on the known composition, equation of
state models can be used to predict the subsequent saturation
pressure as a function of pressure and temperature. In practice,
however, the disparate critical points of the individual components
and insufficiently developed mixing rules for these mixtures made
such prediction useful for qualitative prediction. However,
measurements with a conventional view cell allowed us to determine
the phase envelope with great accuracy and these data will be used
to benchmark our mini PVT system.
[0108] A conventional phase detection view cell was used to
validate measurements obtained with the mini PVT system. This
system includes two sample chambers with volumes of approximately
20 mL each. A magnetically coupled stirrer was used to agitate the
fluid during depressurization. This agitation allowed the fluid to
overcome the nucleation barrier of the phase transition. The two
sample chambers were connected in series and an optical view cell,
installed between the chambers, was used to monitor any phase
change during depressurization. In addition, the pressure was
monitored with a quartzdyne pressure gauge as the volume of the
system was slowly increased, allowing us to confirm the optically
detected phase transition by subtle shifts in the P-V
(pressure-volume) curve.
[0109] An example of the simultaneous measurements undertaken
during depressurization of a single-phase live fluid may be
described as follows. At the beginning of the experiment, the
system is charged with the fluid to be measured. The volume between
the SSB bottles is initially occupied with a pressurized fluid from
a previous experiment and prompts flushing. The pressure in the
sample SSB is elevated to be about 150 psi higher than that in the
waste SSB and valves are opened to allow the sample to flow through
the PVT sensors and into the waste SSB. Note that both pressures
are chosen to be several thousand psi above the bubble point of the
sample. After pumping a volume of sample fluid that is roughly
about 5-10 times that of the mini PVT system volume, the HIP AF1
valves (V1 and V2) are closed and the measurements commence. The
pressure in the isolated portion of the flowline is decreased by
decreasing the pressure on the hydraulic side of the microreactor
piston with an Isco pump.
[0110] The optical intensity of the phase transition cell is
monitored during the depressurization stage. In this example, the
system has been charged with a live oil such that depressurization
results in the production of bubbles. The bubble point is easily
detected when the optical density increases. Two examples are shown
in FIG. 16 where the optical density can be seen to increase
suddenly at approximately 3940 psi when thermal nucleation is
applied, but at 3800 psi when not applied. The former is very close
to that measured by a conventional view cell. FIG. 16A is an
example of the optical signal during depressurization when thermal
nucleation was applied and not applied. The increase in optical
density due to the presence of bubbles occurs at the thermodynamic
saturation pressure (3940 psi, indicated by dashed line) when
thermal nucleation is applied. Without thermal nucleation bubbles
do not emerge until a substantially lower pressure (3800 psi).
[0111] During depressurization the density and viscosity are
simultaneously recorded and the results are presented in FIG. 16B.
This data set was obtained simultaneously with that of FIG. 16A.
Focusing first on the density data, the density decreases slowly as
the pressure is decreased from 5000 psi. This density decrease is
seen in a fluid with properties similar to that of a black oil and
the magnitude of the compressibility will be discussed further in a
subsequent section. At 3800 psi the density rapidly decreases and
becomes less stable as the sample has split into a gas and a liquid
phase in the densitometer. While it is well-known that the liquid
phase becomes denser for pressures below that of the bubble point,
the densitometer is measuring an average density of both the liquid
and gas phases and shows a decrease for pressures below the bubble
point. Once a second phase has formed in the entire system, the
total compressibility increases dramatically and this can be
detected directly in the behavior of the densitometer. This
transition occurs at a pressure far below the thermodynamic
saturation pressure since no thermal nucleation in the
densitometer.
[0112] A similar trend can be observed with the viscosity. The
viscosity of the single phase sample decreases as the pressure is
decreased until gas begins to emerge at 3800 psi. Again, this
bubble point pressure is far below that detected in the phase
transition cell since there is no thermal nucleation in the
vibrating wire viscometer. At this point the viscosity of the
remaining liquid increases, as is seen on measurements of the
viscosity of the liquid phase below that of the saturation
pressure. It can be speculated that the fluid in the viscometer,
like that of the densitometer, has a very low volume fraction of
bubbles unevenly distributed in the fluid. This increase in
measured viscosity therefore indicates that the viscometer wire is
more sensitive to the liquid than the gas phase in this case. Note
that the density of the fluid measured by the vibrating tube
densitometer is employed for calculating the viscosity.
[0113] The phase diagram of the multi-alkane sample was measured
with the mini PVT apparatus over a temperature range from
25.degree. C. to 125.degree. C. using the techniques described
above. The single and multi-phase regions are labeled accordingly
on FIG. 17. FIG. 17 provides a phase diagram measured with the
multi alkane sample. The measurements have been plotted with the
mini PVT cell with and without thermal nucleation, respectively,
measurements with nucleation, are in good agreement with those
measured with the conventional PVT view cell.
[0114] The phase envelope follows the curve one would expect for a
light oil and is rough agreement with the traditional PVT
simulations, but the cricondenbar of the measurements is 400 psi
lower than that of the simulations, illustrating that such
simulators should be used with an appreciation of their
limitations. The saturation pressures measured by the conventional
view cell approach agree very well with the saturation pressures
measured by the mini PVT system when thermal nucleation is applied.
The measurements without thermal nucleation are consistently lower
than those with thermal nucleation for temperatures lower than that
of the cricondenbar. For temperatures above 100.degree. C., the
difference between these two measurements becomes minimal. The
difference between the saturation pressures measured with and
without thermal nucleation is plotted in FIG. 18A and is labeled
"Supersaturation(psi)" because it is shown in pressure and is
indicative of the nucleation barrier which exists for initial
bubble formation in oil samples. This measurement is indicative of
the nucleation behavior of the fluid when charged into the mini PVT
system and does not represent a fundamental property of the fluid.
It was generally observed that the supersaturation decreased as the
temperature was increased. The nucleation barrier in condensate
samples was found to be minimal.
[0115] FIG. 18B is a plot of density as a function of pressure for
low (23.degree. C.) and high (125.degree. C.) temperatures. Arrows
indicate approximate positions of saturation pressures. At the low
temperature, a distinct kink can be seen in the density plot, but
at the high temperature no kink is discernible. This illustrates
why a phase transition cell facilitates determination of the
saturation pressure, especially for samples beyond the critical
point.
[0116] While a small kink can be seen in the density and
viscosity's pressure dependence in FIG. 16B, the phase transition
cell may provide the most certain detection of the saturation
pressure since this is where thermal nucleation takes place. In
FIG. 18B, the pressure dependence of two fluid densities is shown;
one below the critical point and one above, for the multi-alkane
sample. At the lowest temperature (below its critical point), the
density experiences a detectable kink near the phase boundary, as
indicated by the arrow. While this pressure does not correspond to
the thermodynamic saturation pressure, it does show that density
can be used as an indicator of a phase change for a fluid well
below its critical point. However, for the highest temperature,
where the fluid is above the critical temperature, the density
smoothly decreases with pressure with no indication of the phase
change.
[0117] A live oil was obtained downhole with a formation evaluation
tester in order to further test the mini PVT system with a real
crude sample. The fluid was maintained at elevated pressure during
transport at ambient temperature and was homogenized at formation
temperature by rocking for one week. The saturation pressure was
measured from about 22.7.degree. C. to about 148.7.degree. C. and
the optical densities as a function of pressure are plotted for
each temperature in FIG. 19A. The optical intensities have been
shifted for clarity and thermal nucleation was applied during each
of these measurements. The saturation pressure for each temperature
can easily be determined by the deviation of each line from
horizontal. The resulting phase diagram is plotted in FIG. 19B,
including data obtained with and without thermal nucleation. On
average the saturation pressures measured with thermal nucleation
are 200 psi higher than those measured without thermal nucleation.
In this case the measurements with the conventional view cell were
limited to the reservoir temperature, but good agreement may be
seen between the conventional view cell with the saturation
pressure measured with thermal nucleation. Additional information
is available from U.S. patent application Ser. No. 13/800,896,
filed on Mar. 13, 2013 which is incorporated by reference
herein.
[0118] The density for each depressurization temperature is plotted
in FIG. 20A as well as the corresponding viscosity (FIG. 20B). The
high precision of both the vibrating tube densitometer and the
vibrating wire viscometer allows us to resolve small shifts in the
density and viscosity during depressurization. The sharp kink in
the curve for each temperature may indicate that the sample has
broken phase. Note that this apparent saturation pressure does not
correspond to the thermodynamic saturation pressure since there is
no agitation in either the densitometer nor in the viscometer to
overcome the nucleation barrier. For pressures below this kink, the
measured density drops rather rapidly with pressure and the
measured viscosity increases rather rapidly, consistent with the
phase diagram presented in FIG. 19B. In this case, the pressure
dependence of the viscosity appears similar to those found in
standard textbooks concerning the viscosity of the liquid phase of
a live oil about the saturation pressure.
[0119] The high precision of the densitometer enables calculation
the compressibility for each individual temperature (FIG. 21). The
behavior of the compressibility is for that of a black oil,
including the decreased compressibility at high pressure and the
increased compressibility at higher temperature. The waviness seen
in the data at 95 C is an artifact of the densitometer
interpretation and should not be interpreted as a property of the
fluid.
[0120] The operation of a mini PVT apparatus may occur with a total
internal volume of approximately 500 microliters. Some embodiments
may have an internal volume of 300 microliters, 100 microliters, 50
microliters, 30 microliters or 10 microliters. This apparatus is
able to operate at pressure and temperatures consistent with
downhole requirements and exploits novel sensors such as a
microfluidic densitometer, a microfluidic viscometer, and a phase
transition cell that uses thermal nucleation. The compatibility
with true oilfield crude oils and measured a phase diagram that is
consistent with that measured with a conventional view cell that
use a comparatively large volume of fluid.
[0121] Although a few example embodiments have been described in
detail above, those skilled in the art will readily appreciate that
many modifications are possible in the example embodiments without
materially departing from embodiments disclosed herein.
Accordingly, all such modifications are intended to be included
within the scope of this disclosure. In the claims,
means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not only
structural equivalents, but also equivalent structures. Thus,
although a nail and a screw may not be structural equivalents in
that a nail employs a cylindrical surface to secure wooden parts
together, whereas a screw employs a helical surface, in the
environment of fastening wooden parts, a nail and a screw may be
equivalent structures.
* * * * *