U.S. patent application number 09/755228 was filed with the patent office on 2001-08-09 for process and apparatus for coupled electromagnetic and acoustic stimulation of crude oil reservoirs using pulsed power electrohydraulic and electromagnetic discharge.
Invention is credited to Gilbert, William W., Huffman, Alan Royce, Thomas, Sally A..
Application Number | 20010011590 09/755228 |
Document ID | / |
Family ID | 27053594 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011590 |
Kind Code |
A1 |
Thomas, Sally A. ; et
al. |
August 9, 2001 |
Process and apparatus for coupled electromagnetic and acoustic
stimulation of crude oil reservoirs using pulsed power
electrohydraulic and electromagnetic discharge
Abstract
Pulsed power sources are installed in one or more wells in the
reservoir interval. The pulse sources include (1) an
electrohydraulic generator that produces an intense and short lived
electromagnetic pulse that travels at the speed of light through
the reservoir, and an acoustic pulse from the plasma vaporization
of water placed around the source that propagates through the
reservoir at the speed of sound in the reservoir and (2) an
electromagnetic generator that produces only an intense and short
lived electromagnetic pulse that travels at the speed of light
through the reservoir. The combination of electrohydraulic and
electromagnetic generators in the reservoir causes both the
acoustic vibration and electromagnetically-induced high-frequency
vibrations occur over an area of the reservoir where stimulation is
desired. Single generators and various configurations of multiple
electrohydraulic and electromagnetic generators stimulate a volume
of reservoir and mobilize crude oil so that it begins moving toward
a producing well. The method can be performed in a producing well
or wells, an injector well or wells, or special wells drilled for
the placement of the pulsed power EOR devices. The method can be
applied with other EOR methods such as water flooding, CO2
flooding, surfactant flooding, diluent flooding in heavy oil
reservoirs. The recovered formation fluids may be separated into
various constituents.
Inventors: |
Thomas, Sally A.; (Houston,
TX) ; Gilbert, William W.; (Katy, TX) ;
Huffman, Alan Royce; (The Woodlands, TX) |
Correspondence
Address: |
Patricia A. Meier
Conoco Inc. -c/o Joanna K. Payne
100 South Pine, 2635RW
P.O. Box 1267
Ponca City
OK
74603
US
|
Family ID: |
27053594 |
Appl. No.: |
09/755228 |
Filed: |
January 5, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09755228 |
Jan 5, 2001 |
|
|
|
09500669 |
Feb 9, 2000 |
|
|
|
6227293 |
|
|
|
|
Current U.S.
Class: |
166/248 ;
166/303 |
Current CPC
Class: |
E21B 28/00 20130101;
E21B 43/003 20130101 |
Class at
Publication: |
166/248 ;
166/303 |
International
Class: |
E21B 043/00 |
Claims
What is claimed is:
1. A process for recovering a desired constituent of a fluid from
at least one porous zone of a subterranean formation, the method
comprising: (a) generating an electrical pulsed discharge in a
first borehole at a distance from the at least one porous zone and
propagating an electromagnetic wave into the formation at a first
time, said electromagnetic wave reaching the at least one porous
zone at a time substantially equal to the first time and inducing
ultrasonic vibrations within said at least one porous zone; (b)
propagating at a second time an acoustic wave into the formation,
said acoustic wave arriving at said at least one porous zone at a
time substantially equal to the first time and combining with said
ultrasonic vibrations thereby enhancing the mobility of previously
immobile fluid in the at least one porous zone; (c) recovering a
fluid including the mobilized fluid from a producing well in the at
least one porous zone to give a recovered fluid; and (d) using at
least one process selected from gravity separation, fractionation,
cyclone separation, membrane separation, solvent extraction,
cryogenic separation, liquefaction, and pyrolysis to obtain the
desired constituent from the recovered fluid
2. The method of claim 1 further comprising generating the acoustic
wave in the first borehole.
3. The method of claim 1 further comprising generating the acoustic
wave in a second borehole different from the first borehole.
4. The method of claim 2 wherein the electromagnetic wave is
produced by a first pulse generator and the acoustic wave is
produced by a second pulse generator.
5. The method of claim 4 wherein the first and the second pulse
generator each produce electromagnetic and acoustic pulses.
6. The method of claim 4 wherein the first and the second pulse
generator are part of an array including a plurality of pulse
generators, the method further comprising generating at least one
additional electrical pulse for propagating at least one additional
electromagnetic wave at a time after the first time, and
propagating at least one additional acoustic wave, so that the
first acoustic wave is permitted to reach a greater volume of the
reservoir while the first or later electromagnetic wave is still
causing induced acoustic vibration in the reservoir.
7. The method of claim 6 wherein the at least one porous zone
comprises at least two spaced apart porous zones, the method
further comprising activating the plurality of pulse generators at
selected times, said times being selected for enabling an acoustic
and an electromagnetic wave from different pulse generators to
arrive at each of the at least two porous zones at substantially
the same time.
8. The method of claim 1 wherein a difference between the first
time and the second time is selected based upon a velocity of
propagation of the acoustic wave in the formation.
9. The method of claim 1 further comprising introducing a material
selected from (i) steam, (ii) water, (iii) a surfactant, (iv)
diluent, and, (v) CO.sub.2 into the subterranean formation, said
introduced material further enabling at least one of (A) increased
mobility of the reservoir fluid, and, (B) increased flow of the
reservoir fluid.
10. The method of claim 9 wherein introducing the introduced
material into the formation further comprises injecting said
material in an injection well.
11. The method of claim 1 wherein the said first electromagnetic
wave that reaches the at least one porous zone causes a vibration
that has a finite time duration such that the acoustic wave can
pass a given location in the at least one porous zone while the
electromagnetic vibration is still active.
12. The method of claim 4 wherein the said electromagnetic wave,
generated from a pulse generator or generators in an array of pulse
generators, that reaches the at least one porous zone causes a
vibration that has a finite time duration such that the acoustic
wave generated from the first pulse generator can pass a given
location in the at least one porous zone while the ultrasonic
vibration induced by the electromagnetic pulse is still active.
13. The method of claim 1 wherein the electrical pulsed discharge
generates the electromagnetic wave using a magnetic pulse generator
that discharges electricity into a single- or multiple-turn coil,
thus producing an electromagnetic wave, but produces no direct
acoustic wave.
14. The method of claim 1 wherein the pulsed electric discharge is
initiated using a filament of flexible conductive material that
extends across a gap between a pair of electrodes and reduces wear
on the electrodes during discharge, said filament being replaced
after each discharge through an automated spooling feed device that
feeds new filament into the discharge gap through a hole in one of
the electrodes.
15. The method of claim 1 wherein the pulsed electric discharge is
initiated using a pencil-shaped filament of rigid conductive
material that extends across a gap between a pair of electrodes and
reduces wear on the electrodes during discharge, said filament
being replaced after each discharge through an automated feed
device that feeds new filament into the discharge gap through a
hole in one of the electrodes
16. The method of claim 1 wherein the pulsed electric discharge is
initiated using a jet of combustible gas that extends across a gap
between pair of electrodes and reduces wear on the electrodes
during discharge, said gas being applied under pressure through a
hole in one of the electrodes.
17. The method of claim 1 wherein the electrical pulse is produced
by an electrical pulse discharge device is contained within a
packer assembly, said packer assembly being designed to isolate the
discharge device from the rest of the wellbore, and with inflow and
outflow fluid lines so as to provide recirculation of fluids around
the discharge device in the packed off interval, and to apply and
maintain positive fluid pressure to improve the coupling of the
acoustic wave to the wellbore.
18. The method of claim 1 wherein the electrical pulsed discharge
is generated using a reflecting cone that allows the acoustic wave
to be directed at a given azimuth or range of azimuths, said
reflecting cone also being designed to focus the acoustic energy at
a given inclination from the wellbore and also being controlled
such that the energy can be redirected to different azimuths from
time to time during operation by repositioning of the reflecting
cone through a remote control.
19. The method of claim 2 wherein the acoustic wave is generated by
an electrohydraulic discharge device contained within a sleeve of
suitable material that allows propagation of the acoustic wave, but
prevents interaction of a coupling fluid used in the generation of
the acoustic wave with the fluids surrounding the electrohydraulic
discharge device in the wellbore.
20. The method of claim 5 wherein the first and the second pulse
generator are part of an array including a plurality of pulse
generators, the method further comprising generating at least one
additional electrical pulse for propagating at least one additional
electromagnetic wave and acoustic wave, so that the second or later
acoustic wave is permitted to reach a greater volume of the
reservoir while the first or later electromagnetic wave is still
causing induced acoustic vibration in the reservoir.
21. The method of claim 5 wherein the first and the second pulse
generator are part of an array including a plurality of pulse
generators, the method further comprising generating multiple
electrical pulses at the same time, but with variable pulse
durations and energies that permit the simultaneous stimulation of
different scale dependent features with the reservoir.
22. The method of claim 4 wherein the first and the second pulse
generator are part of an array including a plurality of pulse
generators, the method further comprising generating multiple
electromagnetic waves at the same time, but with variable pulse
durations and energies that permit the simultaneous stimulation of
different scale dependent features with the reservoir by
electromagnetirally-induced acoustic vibration.
23. The method of claim 21, further comprising generating at least
one additional electrical pulse for propagating at least one
additional electromagnetic wave and acoustic wave at a time
substantially after the first discharge time, so that the first or
later acoustic wave is permitted to reach a greater volume of the
reservoir while the second or later electromagnetic wave is still
causing induced acoustic vibration in the reservoir.
24. The method of claim 1, the method further comprising
controlling the pulse characteristics of the electromagnetic wave
so that an acoustic vibration induced by the electromagnetic wave
in the reservoir produces vibration frequencies that are optimized
to enhance stimulation at a given scale of inclusion in the
reservoir including (i) the pore scale, (ii) the grain scale, (iii)
the flat crack scale, (iv) the fracture scale, (v) the lamina
scale, (vi) the bedding scale, (vii) the reservoir body length
scale, or (ix) any other scale appropriate for stimulation of
reservoir fluid production.
25. The method of claim 1 wherein the desired constituent is
selected from the group consisting of oil, natural gas, methane,
condensate, casing head gasoline, nitrogen, argon, helium, oxygen,
hydrogen sulfide, carbon dioxide, sulphur dioxide, boron, vanadium,
nickel, sulphur, and asphaltene
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/500,669 filed on Feb. 9, 2000, now U.S.
Pat. No. ______.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention pertains to the stimulation of crude
oil reservoirs to enhance production using a combination of pulsed
power electrohydraulic and electromagnetic methods and the
processing of the recovered crude oil into its components. In
particular, the present invention provides a method and apparatus
for recovery of crude oil from oil bearing soils and rock
formations using pulsed power electrohydraulic and electromagnetic
discharges in one or more wells that produce acoustic and coupled
electromagnetic-acoustic vibrations that can cause oil flow to be
enhanced and increase the estimated ultimate recovery from
reservoirs.
BACKGROUND OF THE INVENTION
[0004] The stimulation of crude oil reservoirs to enhance oil
production from known fields is a major area of interest for the
petroleum industry. One of the single most important research goals
in fossil fuels is to recover more of the hydrocarbons already
found. At present, approximately 66% of discovered oil is left in
the ground due to the lack of effective extraction technology for
secondary and tertiary Enhanced Oil Recovery (EOR). A EOR
technology that can be deployed easily and at low cost in onshore
and offshore field locations would greatly improve the performance
of many oil fields and would increase significantly the world's
known recoverable oil reserves.
[0005] Methods that are widely used for the purpose rely on the
injection of fluid at one well, called the injection well, and use
of the injected fluid to flush the in situ hydrocarbons out of the
formation to a producing well. In one mode of secondary recovery, a
gas such as CO.sub.2 that may be readily available and inexpensive,
is used. In other modes, water or, in the case of heavy oil, steam
may be used to increase the recovery of hydrocarbons. One common
feature of such injection methods is that once the injected fluid
attains a continuous phase between the injection well and the
production well, efficiency of the recovery drops substantially and
the injected fluid is unable to flush out any remaining
hydrocarbons trapped within the pore spaces of the reservoir.
Addition of surfactants has been used with some success, but at
high cost, both economic and environmental.
[0006] Many methods have been developed that try address the
problem of driving out the residual oil. They can be divided into a
number of broad categories.
[0007] The first category uses electrical methods. For example,
U.S. Pat. No. 2,799,641 issued to Bell discloses a method for
enhancing oil flow through electrolytic means. The method uses
direct current to stimulate an area around a well, and uses the
well-documented effect known as electro-osmosis to enhance oil
recovery. Another example of electro-osmosis is described in U.S.
Pat. No. 4,466,484 issued to Kermabon wherein direct current only
is used to stimulate a reservoir. U.S. Pat. No. 3,507,330 issued to
Gill discloses a method for stimulating the near-wellbore volume
using electricity passed upwards and downwards in the well using
separate sets of electrodes. U.S. Pat. No. 3,874,450 issued to Kern
teaches a method for dispersing an electric current in a subsurface
formation by means of an electrolyte using a specific arrangement
of electrodes. Whitting (U.S. Pat. No. 4,084,638) uses high-voltage
pulsed currents in two wells, a producer and an injector, to
stimulate an oil-bearing formation. It also describes equipment for
achieving these electrical pulses.
[0008] A second category relies on the use of heating of the
formation. U.S. Pat. No. 3,141,099 issued to Brandon teaches a
device installed at the bottom of a well that causes resistive
heating in the formation though dielectric or arc heating methods.
This method is only effective within very close proximity to the
well. Another example of the use of heating a petroleum bearing
formation is disclosed in U.S. Pat. No. 3,920,072 to Kern.
[0009] A third category of methods relies on mechanical fracturing
of the formation. An example is disclosed in U.S. Pat. No.
3,169,577 to Sarapuu wherein subsurface electrodes are used to
cause electric impulses that induce flow between wells. The method
is designed to create fissures or fractures in the near-wellbore
volume that effectively increase the drainage area of the well, and
also heat the hydrocarbons near the well so that oil viscosity is
reduced and recovery is enhanced.
[0010] It has long been documented that acoustic waves can act on
oil-bearing reservoirs to enhance oil production and total oil
recovery. A fourth category of methods used for EOR rely on
vibratory or sonic waves, possibly in conjunction with other
methods. U.S. Pat. No. 3,378,075 to Bodine discloses a method for
inducing sonic pumping in a well using a high-frequency sonic
vibrator. Although the sonic energy generated by this method is
absorbed rapidly in the near wellbore volume, it does have the
effect of cleaning or sonicating the pores and fractures in the
near-wellbore area and can reduce hydraulic friction in the oil
flowing to the well. Another example of a vibratory only technique
is disclosed by U.S. Pat. No. 4,049,053 to Fisher et al. wherein
several low-frequency vibrators are installed in the well and are
driven hydraulically using surface equipment. U.S. Pat. No.
4,437,518 issued to Williams describes the design for a
piezoelectric vibrator that can be used to stimulate a petroleum
reservoir. U.S. Pat. No. 4,471,838 issued to Bodine teaches a
method for using surface vibrations to stimulate oil production.
The surface source defined in this patent is not sufficient to
produce significant enhanced recovery of crude oil.
[0011] Turning next to methods that use vibratory or sonic waves in
conjunction with other methods, U.S. Pat. No. 3,754,598 to
Holloway, Jr. discloses a method that utilizes at least one
injector well and another production well. The method imposes
oscillating pressure waves from the injector well on a fluid that
is injected to enhance oil production from the producing well. U.S.
Pat. No. 2,670,801 issued to Sherborne discloses the use of sonic
or supersonic vibrations in conjunction with fluid injection
methods: the efficiency of the injected fluids in extracting
additional oil from the formation is improved by the use of the
acoustic waves. U.S. Pat. No. 3,952,800, also to Bodine teaches a
sonic treatment in which a gas is injected into the well and is
used to treat the wellbore surface using sonic wave stimulation.
The method causes the formation to be heated through the gas by
heating from the ultrasonic vibrations. U.S. Pat. No. 4,884,634
issued to Ellingsen uses vibrations of an appropriate frequency at
or near the natural frequency of the formation to cause the
adhesive forces between the formation and the oil to break down.
The method calls for a metallic liquid (mercury) to be placed in
the wells to the level of the reservoir and the liquid is vibrated
while also using electrodes placed in the wells to electrically
stimulate the formation. Apart from the potential environmental
hazards associated with the handling and containment of mercury,
this method faces the problem of avoiding formation damage due to
an excess of borehole pressure over the formation fluid pressure
caused by the presence of a dense liquid. U.S. Pat. No. 5,282,508,
also issued to Ellingsen et al. defines an acoustic and electrical
method for reservoir stimulation that excites resonant modes in the
formation using AC and/or DC currents along with sonic treatment.
The method uses low frequency electrical stimulation.
[0012] The success of the existing art in stimulating reservoirs
has been spotty at best, and the effective range of such methods
has been limited to less than 1000 feet from the stimulation
source. A good discussion on wettability, permeability, capillary
forces and adhesive and cohesive forces in reservoirs is provided
by the Ellingsen '508 patent. These discussions fairly represent
the state of knowledge on these subjects and are not repeated
herein. These discussions do not, however, address the limitations
on the current state of the art in acoustic stimulation.
[0013] Existing acoustic stimulation methods have demonstrated
clearly that they are limited to a range of about 1000 feet from
the stimulation point. This limit is caused by the natural
attenuation properties of the reservoir, which absorb high
frequencies preferentially and reduce the effective frequency range
to less than a few hundred Hertz at distances beyond about 1000
feet from the acoustic source. This same limit has plagued seismic
imaging in cross-borehole studies for many years and is a
fundamental physical limitation on all acoustic methods.
[0014] Effective acoustic stimulation of oil-bearing reservoirs
requires support at greater distances from the stimulation source
than possible with most of the prior art. In addition, there is
some empirical evidence suggesting that higher frequencies than
direct acoustic methods can generate may be more effective in
stimulation of oil-bearing reservoirs. Accordingly, it is desirable
to have a stimulation source that has a greater range of
effectiveness than the prior art discussed above. Such a source
should preferably be able to provide stimulation at higher
frequencies than the 10-500 Hz typically attainable using prior art
methods.
[0015] U.S. Pat. No. 4,345,650 issued to Wesley teaches a device
for electrohydraulic recovery of crude oil using by means of an
electrohydraulic spark discharge generated in the producing
formation in a well. This method presents an elegant apparatus that
can be placed in the producing interval and can produce a shock and
acoustic wave with very desirable qualities. The present invention
will build on the teachings of this patent and will extend the
effective range of Wesley's method through new and novel equipment
designs and field configurations of Wesley's apparatus and new
apparatus designed to enhance the effect on oil reservoirs.
[0016] Hydrocarbons recovered from a wellbore may include a number
of components. The term "crude oil" is used to refer to
hydrocarbons in liquid form. The API gravity of crude oil can range
from 6.degree. to 50.degree. API with a viscosity range of 5 to
90,000 cp under average conditions. Condensate is a hydroacarbon
that may exist in the producing formation either as a liquid or as
a condensable vapor. Liquefaction of the gaseous components occurs
when the temperature of the recovered hydrocarbons is lowered to
typical surface conditions. Recovered hydrocarbons also include
free gas that occurs in the gaseous phase under reservoir
conditions, solution gas that comes out of solution from the liquid
phase when the temperature is lowered, or as condensable vapor.
Recovered hydrocarbons also commonly include water that may be in
either liquid form or vapor (steam). The liquid water may be free
or emulsified: free water reaches the surface separated from liquid
hydrocarbons whereas the emulsified water may be either water
dispersed as an emulsion in liquid hydrocarbons or as liquid
hydrocarbons dispersed as an emulsion in water. Produced well
fluids may also include gaseous impurities including nitrogen,
helium and other inert gases, CO.sub.2, SO.sub.2 and H.sub.2S.
Solids present in the recovered wellbore fluids may include
sulphur. Heavy metals such as chromium, vanadium or manganese may
also be present in the recovered fluids from a wellbore, either as
solids or in solution as salts. In all enhanced EOR operations, it
is desirable to separate these and other commercially important
materials from the recovered fluids.
SUMMARY OF THE INVENTION
[0017] The present invention is a pulsed power device and a method
of using the pulsed power device for EOR. Pulsed power is the rapid
release of electrical energy that has been stored in capacitor
banks. By varying the inductance of the discharge system, energies
from 1 to 100,000 Kilojoules can be released over a pulse period
from 1 to 100 microseconds. The rapid discharge results in a very
high power output that can be harnessed in a variety of industrial,
chemical, or medical applications. The energy release from the
system can be used either in a direct plasma mode through a spark
gap or exploding filament, or by discharging the energy through a
single- or multiple-turn coil that generates a short-lived but
extremely intense magnetic field.
[0018] When electricity stored in capacitors is released across a
spark gap submerged in water, a plasma channel is created that
vaporizes the surrounding water. This plasma ionizes the water and
generates very high pressures and temperatures as it expands
outward from the discharge point. In a plasma, or electrohydraulic
(EH) mode, the pulse may be used in a wide range of processes
including geophysical exploration, mining and quarrying, precision
demolition, machining and metal forming, treatment and purification
of a wide range of fluids, ice breaking, defensive weaponry, and
enhanced oil recovery which is the purpose of the present
invention. The basic physics of the shock wave that is generated by
the EH discharge is well understood and is documented in U.S. Pat.
No. 4,345,650 issued to Wesley, and incorporated herein by
reference.
[0019] In the electromagnetic (EM) mode, the coil is designed to
produce controlled flux compression that can be used to generate
various physical effects without the coupled effect of the EH
strong acoustic wave. In both systems, however, typical systems
require about 0.5 to 1 seconds to accumulate energy from standard
power sources. The ratio of accumulation time to discharge time
(100,000 to 1,000,000) allows the generation of pulses with several
gigawatts of peak power using standard power sources.
[0020] Given the physical limitations on direct acoustic
stimulation caused by attenuation in natural materials, acoustic
stimulation must be generated using wide band vibrations in these
materials at distances much greater than the current limitation of
about 1000 feet. The present invention addresses this issue in a
new and innovative way using pulsed power as the source. The Wesley
'650 patent teaches a method for generating strong acoustic
vibrations for reservoir stimulation that has been shown in the
field to have an effective limit of about 1000 feet. What was not
recognized in the Wesley teachings was that the pulsed power method
also has a unique ability to generate high-frequency acoustic
stimulation of the reservoir separately from the direct acoustic
response of the EH shock wave generated by the plasma discharge in
the wellbore. In addition to the direct shock wave effect claimed
in the Wesley patent, the pulsed power discharge also generates a
strong electromagnetic pulse that travels at the speed of light
across the reservoir. As this electromagnetic pulse transits the
reservoir, it induces a coupled acoustic vibration at very high
frequencies in geologic materials like quartz that causes
stimulation at multiple scales in the reservoir body. This induced
acoustic vibration acts for a short period of time after the pulse
is discharged, usually on the order of about 0.1 to 0.3 seconds,
but is induced everywhere that the electromagnetic pulse travels.
Thus, it is not limited by the natural acoustic attenuation that
limits the effectiveness of a direct acoustic pulse source because
it is induced at all locations in-situ by the electromagnetic
pulse. At the same time, the lower-frequency direct acoustic pulse
travels through the reservoir at the velocity of sound. This direct
acoustic pulse assists the electromagnetically-induced vibrations
in stimulating the reservoir, but has a clearly limited range due
to the finite speed that it can travel before the EM-induced
vibrations decay and become ineffective.
[0021] Effective acoustic stimulation of oil-bearing reservoirs
requires higher frequencies than direct acoustic methods can
generate and support at great distances from the stimulation
source. Every rock formation can be modeled as a uniform equivalent
medium with imbedded inclusions. These inclusions can be present at
the pore scale, grain scale, crack scale, lamina scale, bedding
scale, sand body scale, and larger scales. Each of these
inclusions, or features, of the formation act as scatterers that
absorb acoustic energy. The frequency of the energy absorbed is
directly correlated to the scale of the inclusions and the contrast
in physical properties between the inclusion and the surrounding
matrix, and this absorption provides the energy for enhanced oil
recovery that is required at a specific scale of inclusion. Hence,
an effective acoustic stimulation program can be designed to
optimize the energy absorption and effective stimulation if the
scale of the inclusions and their physical properties are known,
and if the acoustic stimulation frequencies can be targeted at
these inclusion scales over a large volume of the reservoir. The
limitations and variations in the effectiveness of existing
acoustic methods are directly correlated to the narrow band of
seismic frequencies from 10-500 hertz used to stimulate and whether
there are inclusions at those frequencies within the effective
range of the stimulation method in question. When this physical
understanding of the role of acoustic absorption by scale dependent
features in reservoirs is included, it becomes readily apparent why
existing acoustic methods with a frequency band limited to a few
hundred hertz are not capable of stimulating most reservoirs
effectively. The existing technology has demonstrated a spotty
record because the narrow band of frequencies used are often not
the right ones for stimulating the critical inclusions of a
particular reservoir. The scale of the inclusions that are critical
to effective stimulation exist at the Dore scale, grain scale,
flat-crack scale, and fracture scale, all of which are activated by
much higher frequencies (kilohertz and higher) than the band pass
of the low-frequency direct acoustic wave.
[0022] The present invention differs from all of the prior art in
several ways. First, it uses a coupled process of direct EH
acoustic vibrations that propagate outward into the formation from
one or more wells, and electromagnetically-induced high-frequency
acoustic vibrations that are generated using both EH and EM pulsed
power discharge devices that takes advantage of the acoustic
coupling between the electromagnetic pulse and the formation. This
is significantly different from the prior art which relies on
acoustic vibrations only, or a combination of acoustic vibrations
and low-frequency AC or DC electrical stimulation.
[0023] The present invention also recognizes that these two effects
must occur together to effectively mobilize the oil and increase
production of the oil. The problem that arises is that the
EM-induced vibrations only occur for a short time after the
electrohydraulic or electromagnetic pulse is initiated. The
electrohydraulic acoustic pulse travels at a finite speed from the
well where the pulse originates, so that the effective range of the
technique is defined by how far the acoustic wave can travel before
the electromagnetically-induced vibration in the reservoir ceases.
Hence, a single pulse source has a range that is limited by the
pulse characteristics employed.
[0024] In a preferred embodiment of the present invention, the
technique can be applied using a multi-level discharge device that
allows sequential firing of several sources in one well in a time
sequence that is optimized to allow continuous
electromagnetic-coupled stimulation of a large reservoir volume
while the electrohydraulic acoustic pulse travels further from the
pulse well than it could before a single source electromagnetic
vibration would decay. This approach can be used to extend the
effective range of the stimulation by a factor of 5-6 from about
1000 feet as claimed and proven in the Wesley patent, i.e., up to
distances of 5000 to 6000 feet claimed in the present invention.
This allows the technique to be applied effectively to a wide range
of oil fields around the world. This concept can be extended to the
placement of multiple tools in multiple wells to achieve better
stimulation of a specific volume of the reservoir.
[0025] In another embodiment of the invention, the range of the
technique is extended by using multiple pulse sources in multiple
wells that allow the electromagnetically-induced vibrations to
continue for a longer time, thus allowing the acoustic pulse to
travel further into the formation, effectively extending the range
of coupled stimulation that can be achieved. This embodiment
utilizes a time-sequential discharge pattern that produces a series
of electromagnetically-induced vibrations that will last up to
several seconds while the direct acoustic pulse travels further
from the discharge source to interact with the
electromagnetically-induced vibrations at much greater distances in
the reservoir.
[0026] In another embodiment of the present invention, multiple EH
and EM sources can be placed in multiple wellbores and discharged
to act as an array that will stimulate production of the oil in a
given direction or specific volume of the reservoir.
[0027] In another aspect of the invention, the discharge
characteristics of the pulse sources can be customized to produce
specific frequencies that will achieve optimal stimulation by
activating specific scales of inclusions in the reservoir. In this
embodiment, the discharge devices can have their inductances
modified to achieve a variety of pulse durations and peak
frequencies that are tuned to the specific reservoir properties.
This allows for the design of a multi-spectral stimulation program
that can activate those inclusions that are critical to enhanced
production, while preventing activation of those inclusions that
might inhibit enhanced production. Once the desired inclusions for
stimulation are defined by conventional geophysical logging
methods, a reservoir model is constructed and the optimal
frequencies for the stimulation are determined. The pulse tool can
be adapted to a wide range of pulse durations and peak frequencies
by adjusting the induction of the capacitor circuits in the pulse
tool. Where multiple frequencies are desired to achieve stimulation
at several scales, the multi-level tool in a single well or
multiple tools placed in multiple wells can be tuned to the
reservoir to optimize the desired stimulation effect and produce a
multi-spectral stimulation of the reservoir.
[0028] The present invention also differs from the previous art in
that it includes the use of EM pulse sources that do not generate a
direct acoustic shock pulse like the plasma shock effect caused by
the spark gap in the electrohydraulic device defined by Wesley.
These pulse sources replace the conventional spark gap discharge
device defined by Wesley with a single-turn magnetic coil that
produces a magnetic pulse with no acoustic pulse effect. This tool
can be placed in more sensitive wells that will not tolerate the
strong shock effect of an EH pulse generator. They also allow a
wider range of discharge pulse durations that will extend the
effective frequency range of induced vibrations that can be applied
to a given reservoir.
[0029] In another embodiment of the present invention, the EH pulse
source can be directed using a range of directional focusing and
shaping devices that will cause the acoustic pulse to travel only
in specific directions. This reflector cone allows the operator to
aim the pulses from one or multiple wells so that they can effect
the specific portion of the formation where stimulation is
desired.
[0030] In another embodiment of the present invention, the pulse
source is placed in an injector well that is being used for water
injection, surfactant injection, diluent injection, or CO2
injection. The tool can be configured to operate in a rubber sleeve
to isolate it, where appropriate, from the fluids being injected.
The tool can be deployed in a packer assembly suspended by
production tubing, and can be bathed continuously in water to
maintain good coupling to the formation. Gases generated by the
electrohydraulic discharge can be removed from the packer assembly
by pumping water down the well and allowing the gases to be flushed
back up the production tubing to maintain optimal coupling and
avoid the increase in compressibility that would occur if the gases
were left in the well near the discharge device.
[0031] A chronic problem with electrohydraulic discharge devices is
that the electrodes are prone to wear and must be replaced from
time to time. In another embodiment of the present invention, the
electrodes designed for electrohydraulic stimulation have been
improved using several methods including (1) improved alloys that
withstand the pulse discharge better and last longer, (2) two new
feeding devices for exploding filaments, one with a hollow
electrode using a pencil filament, and one with a rolled filament
on a spool, that allows the exploding filament to be threaded
across the spark gap rapidly between discharges so that the pulse
generator can operate more efficiently, and (3) gas injection
through a hollow electrode that acts as a spark initiation
channel.
[0032] In another embodiment of the invention, the fluids produced
from the wellbore are separated into its components. These
components may include one or more of associated gas, condensate,
liquid hydrocarbons, helium and other noble gases, carbon dioxide,
sulphur dioxide, pyrite, paraffins, heavy metals such as chromium,
manganese and vanadium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a diagram of the basic configuration of the tool
as deployed in a wellbore, including the surface equipment, winch
truck and control panel, and showing the activation of various
scales of the reservoir in a blow-up insert to the diagram.
[0034] FIG. 2 is a diagram showing improvements in the basic
one-level tool from U.S. Pat. No. 4,345,650 of Wesley.
[0035] FIG. 3 is a diagram showing the design of a multi-level tool
allowing time sequential and variable inductance discharges with
both EH and EM discharge devices under user control.
[0036] FIG. 4 is a schematic diagram showing the design of a
single-turn coil EM discharge device for the tool with rubber
sleeve for electrical isolation
[0037] FIG. 5 is a schematic diagram showing the activation of a
reservoir adjacent to the tool with a multi-level discharge
device.
[0038] FIG. 6 is a schematic diagram showing the deployment of
multiple tools in multiple wells to act as a source array.
[0039] FIG. 7 is a schematic diagram showing the deployment of a
tool contained in a packer assembly in an injector well with tubing
to feed water and electrical and control leads.
[0040] FIG. 8. is a schematic diagram showing the design of the
tool incorporating a sleeve exploder configuration for non-packer
applications.
[0041] FIG. 9 is a schematic diagram showing the design of the
directional energy cone for the EH discharge device.
[0042] FIG. 10 is a schematic diagram showing the design of hollow
EH electrodes with a pencil exploding filament device.
[0043] FIG. 11 is a schematic diagram showing the design of hollow
EH electrodes with a spooled feeding device for an exploding
filament.
[0044] FIG. 12 is a schematic diagram showing the design of hollow
electrodes with a gas-injection device for improving electrode
wear.
DETAILED DESCRIPTION OF THE INVENTION
[0045] FIG. 1 shows a wellbore 1 drilled in the subsurface of the
earth penetrating formations 7, 9, 11, 13, 15 . . . . The wellbore
1 is typically filled with a drilling fluid 5 known in the art as
"drilling mud.". The sonde 21 that forms part of the present
invention is conveyed downhole, in the preferred embodiment of the
present invention, on an armored electrical cable, commonly called
a wireline 3.
[0046] The wireline is supported by a derrick 19 or other suitable
device and may be spooled onto a drum (not shown) on a truck 25. By
suitable rotation of the drum, the downhole tool may be lowered to
any desired depth in the borehole. In FIG. 1, for illustrative
purposes, the downhole tool is shown as being at the depth of the
formation 11. This is commonly a hydrocarbon reservoir from which
recovery of hydrocarbons is desired. An uphole power source 33 and
a surface control unit 23 provide electrical power and control
signals through the electrical conductors in the wireline to the
sonde 21. In FIG. 1, the sonde is depicted as generating energy
pulses 35 into one of the subsurface formations.
[0047] The control unit 23 includes a power control unit 25 that
controls the supply of power to the sonde 21. The surface control
unit also includes a fire control unit 27 that is used to initiate
generation of the energy pulses 35 by the sonde. Another component
of the surface control unit 23 is the inductance control unit 29
that controls the pulse duration of the energy pulses 35. Yet
another component of the surface control unit is the rotation
control 31 that is used to control the orientation of components of
the sonde 35. The functions of the power control unit 25, the fire
control unit 27, the inductance control unit 29 and the rotation
control unit 31 are discussed below in reference to FIG. 3.
[0048] One embodiment of the invention is a tool designed for
operation at a single level in a borehole. This is illustrated in
FIG. 2 that is a view of the sonde 21 and the major components
thereof as adapted to be lowered into the well. The basic EH sonde
is an improvement over that disclosed in U.S. Pat. No. 4,345,650
issued to Wesley and the contents of which are fully incorporated
here by reference.
[0049] One set of modifications relates to the use of processors
wherever possible, instead of the electronic circuitry. This
includes the surface control unit 23 and its components as well as
in the downhole sonde.
[0050] In a preferred embodiment of the invention, the sonde 21 is
used within a cased well, though it is to be understood that the
present invention may also be used in an uncased well. The sonde 21
comprises an adapter 53 that is supported by a cable head adapter
55 for electrical connection to the electrical conductors of the
wireline 3. The sonde 21 includes a gyro section 57 that is used
for establishing the orientation of the sonde and may additionally
provide depth information to supplement any depth information
obtained uphole in the truck 25 based upon rotation of the take-up
spool. The operation of the gyro section 57 would be known to those
versed in the art and is not discussed further. The gyro section 57
here is an improvement over the Wesley device and makes it possible
to controllably produce energy pulses in selected directions.
[0051] The other main components of the sonde 21 are a power
conversion and conditioning system 59, a power storage section 63,
a discharge and inductance control section 65, and the discharge
section 67. A connector 69 couples the power conversion and
conditioning section to the power storage section 63. The power
storage section 63, as discussed in the Wesley patent, comprises a
bank of capacitors for storage of electrical energy. Electrical
power is supplied at a steady and relatively low power from the
surface through the wireline 3 to the sonde and the power
conversion and conditioning system includes suitable circuitry for
charging of the capacitors in the power storage section 63. Timing
of the discharge of the energy in the power from the power storage
section 63 through the discharge section 67 is accomplished using
the discharge and induction control section 65 on the basis of a
signal from the fire control unit (27 in FIG. 1). Upon discharge of
the capacitors in the power storage section 63 through the
discharge section 67 energy pulses are transmitted into the
formation. In one embodiment of the invention, the discharge
section 67 produces EH pulses. Refinements in the design of the
discharge section 67 over that disclosed in the Wesley patent are
discussed below with reference to FIGS. 9-12.
[0052] Turning now to FIG. 3, an embodiment of the invention
suitable for use with multiple levels of energy stimulation into
the formation is illustrated. The downhole portion of the apparatus
comprises a plurality of sondes 121a, 121b, . . . 121n. For
illustrative purposes, only three sondes are shown. The coupling
between two of the sondes 121a and 121b is illustrated in detail in
the figure. Eyehooks 141 and 143 enable sonde 121b to be suspended
below sonde 121a. This eyehook arrangement allows for a limited
rotation of sonde 121b relative to sonde 121a. Flexible electrical
leads 153 carry power and signals to the lower sonde 121b and the
eyehooks ensure that the leads 153 are not subjected to stresses
that might cause them to break. The leads are carried within
support post 151 in the upper sonde 121a. A similar arrangement is
used for suspending the remaining sondes.
[0053] Each of the sondes 121a, 121b . . . 121n has corresponding
components in the surface control unit 123. Illustrated are power
control units 125a, 125b . . . 125n for power supply to the sondes;
inductance control units 127a, 127b . . . 127n for inductance
control; rotation control units 129a, 129b . . . 129n for
controlling the rotation of the various sondes relative to each
other about the longitudinal axes of the sondes (see rotation
bearing 71 in FIG. 2); and inclination control unites 131a, 131b, .
. . 131n for controlling the inclination of the discharge sections
(see 67 in FIG. 2) of the sondes relative to the horizontal. In
addition, the surface control unit also includes a fire control and
synchronization unit 135 that controls the sequence in which the
different sondes 121a, 121b, . . . 121n are discharged to send
energy into the subsurface formations.
[0054] Turning next to FIG. 4, an EM pulse source is depicted. This
is a single-turn magnetic coil that produces a magnetic pulse with
no significant acoustic pulse. This tool can be placed in more
sensitive wells that will not tolerate the strong shock effect of
an EH pulse generator. It also allows a wider range of discharge
pulse durations that will extend the effective frequency range of
induced vibrations (up to 100 microseconds) that can be applied to
a given reservoir.
[0055] The input electrical power is supplied by a conductor 161.
The EM discharge device comprises a cylindrical single-turn
electromagnet 179 having an annular cavity 174 filled with
insulation 175. The electromagnet body is separated by rubber
insulation 173 from the steel top plate 164 and the steel base
plate 181. Steel support rods 171 couple the steel top plate 164
and the steel base plate 181. The whole is within a nonconductive
housing 163 with an expansion gap between the steel base plate 183.
Optionally, provision may be made for circulating a cooling liquid
between the electromagnet body 179 and the rubber insulation 173.
The electromagnet does not allow current to flow back out of the
device, which results in dissipative resistive heating of the
magnet from each pulse, hence the potential need for a cooling
medium if rapid discharge is desired.
[0056] Turning next to FIG. 5, the different scales at which the
flow of reservoir fluids in the subsurface is depicted. Depicted
schematically are four energy sources 211, 213, 215 and 217 within
a borehole 201. Waves 200a from source 211 are depicted as
propagating into formations 221,223 and 225 to stimulate the flow
of hydrocarbons therein. The frequency of these waves is selected
to stimulate flow on the scale of bedding layers: typically, this
is of the order of a few centimeters to a few meters.
[0057] The energy source 217 is shown propagating waves 200d into
the subsurface to stimulate flow of hydrocarbons from fractures 227
therein. As would be known to those versed in the art, these
fractures may range in size from a few millimeters to a few
centimeters. Accordingly, the frequency associated with the waves
200d would be greater than the frequency associated with the waves
200a.
[0058] Also shown in FIG. 5 are waves 200b and 200c from sources
213 and 215 are depicted as propagating into the formation to
stimulate flow of hydrocarbons on the scale of grain size 229 and
pore size 231. Typical grain sizes for subsurface formations range
from 0.1 mm to 2 mm. while pore sizes may range from 0.01 mm to
about 0.5 mm, so that the frequency for stimulation of hydrocarbons
at the grain size scale is higher than for the fractures and the
frequency for stimulation of flow at the pore size level is higher
still.
[0059] As would be known to those versed in the art, the discharge
of a capacitor is basically determined by the inductance and
resistance of the discharge path. Accordingly, one function of the
inductance control units (27 in FIG. 1; 65 in FIG. 2; 127a . . .
127n in FIG. 3) in the invention is to adjust the rate of discharge
(the pulse duration) and the frequency of oscillations associated
with the discharge.
[0060] FIG. 6a is a plan view of an arrangement of wells using the
present invention. Shown is a producing well 253 and a number of
injection wells 251a, 251b, 251c . . . 251n. Each of the wells
includes a source of EH or EM energy. Shown in FIG. 6a are the
acoustic waves 255a, 255b . . . 255n propagating from the injection
wells in the formation towards the producing well. When sources in
all the injection wells 251a, 251b, 251c . . . 251n are discharged
simultaneously, then the acoustic wavefronts, depicted here by 257a
. . . 257n propagate through the subsurface as shown and arrive at
the producing well substantially simultaneously, so that the
stimulation of hydrocarbon production by the different sources
occurs substantially simultaneously.
[0061] One or more of the wells 251a, 251b, 251c . . . 251n may be
used for water injection, surfactant injection, diluent injection,
or CO2 injection using known methods. The tool can be configured to
operate in a rubber sleeve to isolate it, where appropriate, from
the fluids being injected. The tool can be deployed in a packer
assembly suspended by production tubing, and can be bathed
continuously in water to maintain good coupling to the formation.
Gases generated by the electrohydraulic discharge can be removed
from the packer assembly by pumping water down the well and
allowing the gases to be flushed back up the production tubing to
maintain optimal coupling and avoid the increase in compressibility
that would occur if the gases were left in the well near the
discharge device. This is discussed below with reference to FIGS. 7
and 8.
[0062] FIG. 6b shows a similar arrangement of injection wells 251a,
251b . . . 251n and a producing well 253. However, if the sources
in the injection well are excited at different times by the surface
control unit, then the acoustic waves 255a', . . . 255n' appear as
shown and the corresponding wavefronts 257a', . . . 257n' arrive at
the producing well at different times. In the example shown in FIG.
6b, the acoustic wave 257c' from well 251c is the first to
arrive.
[0063] In both FIG. 6a and 6b, the injection wells have been shown
more or less linearly arranged on one side of the producing well.
This is for illustrative purposes only and in actual practice, the
injection wells may be arranged in any manner with respect to the
producing well. Those versed in the art would recognize that with
the arrangement of either 6a or 6b, the frequencies of the acoustic
pulses may be controlled to a limited extent by controlling the
pulse discharge in the sources using the inductance controls of the
surface control unit. As noted in the background to the invention,
these acoustic waves will have a limited range of frequencies.
However, when combined with the large range of frequencies possible
with the EM waves, the production of hydrocarbons may be
significantly improved over prior art methods.
[0064] Turning now to FIG. 7, a tool of the present invention is
shown deployed in a cased borehole within a formation 301. The
casing 305 and the cement 303 have perforations 307 therein. An
upper packer assembly 309 and a lower packer assembly 311 serve to
isolate the source and limit the depth interval of the well over
which energy pulses are injected into the formation. In addition to
the power supply 313, provision is also made for water inflow 315
and water outflow 317. The outflow carries with it any gases
generated by the excitation of the source 319. With the provision
of the water supply, the borehole between the packers 309, 311 is
filled with water or other suitable fluid and is in good acoustic
coupling with the formation. This increases the efficiency of
generation of acoustic pulses into the formation.
[0065] An alternate embodiment of the invention that does not use
packer assemblies is schematically depicted in FIG. 8 wherein a
tool of the present invention is shown deployed in a cased borehole
within a formation 351. The casing 355 and the cement 353 have
perforations (not shown). As in the embodiment of FIG. 7, in
addition to the power supply 363, provision is also made for water
inflow 365 and water outflow 367. The outflow carries with it any
gases generated by the excitation of the source 369. The tool is
provided with a flexible sleeve 373 that is clamped to the body of
the tool by clamps 371 and 375. The sleeve isolates the fluid
filled wellbore 357 from the water and the explosive source within
the sleeve while maintaining acoustic coupling with the
formation.
[0066] Turning now to FIG. 9, an embodiment of the invention
allowing for directional control of the outgoing energy is
illustrated. The tool 421 includes a bearing 403 that allows for
rotation of the lower portion 405 relative to the upper portion
401. This rotation is accomplished by a motor (not shown) that is
controlled from the surface control unit. By this mechanism, the
energy may be directed towards any azimuth desired. In addition,
the tool includes a controller motor that rotates a threaded
rotating post 409. Rotation of the post 409 pivots a pulse director
412 in a vertical plane, and a substantially cone-shaped opening in
the pulse director directs the outgoing energy in the vertical
direction.
[0067] A common problem with prior art spark discharge devices is
damage to the electrodes from repeated firing. One embodiment of
the present invention that addresses this problem is depicted in
FIG. 10. Shown are the electrodes 451 and 453 between which an
electrical discharge is produced by the discharge of the capacitors
discussed above with reference to FIG. 2. The electrode 451
connected to the power supply (not shown) is referred to as the
"live" electrode. In such spark discharge devices, the greatest
amount of damage occurs to the live electrode upon initiation of
the spark discharge. In the device shown in FIG. 10, the live
electrode is provided with a hollow cavity 454 through which a
pencil electrode 457 passes. The pencil electrode 457 is designed
to be expendable and initiation of the spark discharge occurs from
the pencil electrode while the bulk of the electrical discharge
occurs from the live electrode 451 after the spark discharge is
initiated. This greatly reduces damage to the live electrode 451
with most of the damage being limited to the end 459 of the pencil
electrode from which the spark discharge is initiated. The device
is provided with a motor drive 455 that feeds the pencil electrode
457 through the live electrode upon receipt of a signal from the
control unit received through the power and control leads 455. In
one embodiment of the invention, this signal is provided after a
predetermined number of discharges. Alternatively, a sensor (not
shown) in the downhole device measures wear on the pencil electrode
and sends a signal to the control unit.
[0068] Another embodiment of the invention illustrated
schematically in FIG. 11 uses a filament for the initiation of the
spark discharge. The power leads (not shown) are connected to the
live electrode 501 as before, and the return electrode 503 is
positioned in the same way as before. The filament 511 is wound on
a spool 509 and is carried between rollers 513 into a hole 504
within the live electrode. The spark is initiated at the tip 515 of
the filament 511. The filament 511 gets consumed by successive
spark discharges and additional lengths are unwound from the spool
509 as needed using the power and control leads 505.
[0069] FIG. 12 shows another embodiment of the invention wherein a
gas 561 is conveyed through tubes 563 and 565 to the hollow lower
electrode 553 via a threaded pressure fitting 569. The lower
electrode is coupled by means of a thread to the bottom plate 567.
The flowing gas gets ionized by the potential difference between
the lower electrode 553 and the upper electrode 551. The initiation
of the spark takes place in this ionized gas, thereby reducing
damage to the electrodes 551 and 553.
[0070] There are a number of different methods in which the various
embodiments of the device discussed above may be used. Central to
all of them is the initiation of an electromagnetic wave into the
formation. The EM wave by itself produces little significant
hydrocarbon flow on a macroscopic scale; however, it does serve the
function of exciting the hydrocarbons within the formation at a
number of different scales as discussed above with reference to
FIG. 5. This EM wave may be produced by an electromagnetic device,
such as is shown in FIG. 4, or may be produced as part of an EH
wave by a device such as described in the Wesley patent or
described above with reference to FIGS. 10, 11 or 12. This EM wave
is initiated at substantially the same time as the arrival of the
acoustic component of an earlier EH wave at the zone of interest
from which hydrocarbon recovery is desired. Any suitable
combination of EH and EM sources fired at appropriate times may be
used for the purpose as long as an EM and an acoustic pulse arrive
at the region of interest at substantially the same time.
[0071] For example, a single EH source as in FIG. 1, may be fired
in a repetitive manner so that acoustic pulses propagate into the
layer 11: the EM component of later firings of the EH source will
then produce the necessary conditions for stimulation of
hydrocarbon flow at increasing distances from the wellbore 1. Also
by way of example, a vertical array of sources such as is shown in
FIG. 5 may be used to propagate EM and acoustic pulses into the
formation to stimulate hydrocarbon flow from different formations
and from different types of pore spaces (fractures, intragranular,
etc.). EH and/or EM sources may be fired from a plurality of
wellbores as shown in FIG. 6a, 6b to stimulate hydrocarbon flow in
the vicinity of a single production well. The sources may be
oriented in any predetermined direction in azimuth and elevation
using a device as shown in FIG. 9. In any of the arrangements,
additional materials such as steam, water, a surfactant, a diluent
or CO.sub.2 may be injected into the subsurface. The injected
material serves to increased the mobility of the hydrocarbon,
and/or increase the flow of hydrocarbon.
[0072] The primary purpose of using electrohydraulic stimulation as
described above is the recovery of hydrocarbons from the subsurface
formations. However, as noted above in the Background of the
Invention, the fluids recovered from a producing borehole may
include a mixture of hydrocarbons and water and additional material
such as, solids, CO.sub.2, H.sub.2S, SO.sub.2, inert gases
[0073] H. Vernon Smith in Chapter 12 of the Petroleum Engineering
Handbook (Society of Petroleum Engineers), and the contents of
which are fully incorporated herein by reference, reviews devices
known as Oil and Gas Separators, that are normally used near the
wellhead, manifold or tank battery to separate fluids produced from
oil and gas wells into oil and gas or liquid and gas. In one
embodiment of the present invention, any of the devices discussed
in Smith may be used to separate fluids produced by the
electrohydraulic stimulation discussed above. Favret (U.S. Pat. No.
3,893,918), the contents of which are fully incorporated herein by
reference, teaches a fractionation column for separation of oil
from a fluid mixture containing oil. Kjos (U.S. Pat. No.
5,860,476), the contents of which are incorporated herein by
reference, teaches an arrangement in which a first cyclone
separator is used to separate gas and liquid, a second cyclone
separation is used to separate condensate/oil from water, and a
membrane separation us used to separate gases including H.sub.2S,
CO.sub.2 , and SO.sub.2. U.S. Pat. No. 4,805,697 to Fouillout et
al, the contents of which are fully incorporated herein by
reference, teaches a method in which recovered fluids from the
wellbore are separated into an aqueous and a light phase consisting
primarily of hydrocarbons and the aqueous phase is reinjected into
the producing formation.
[0074] U.S. Pat. No. 6,085,549 to Daus et al., the contents of
which are fully incorporated herein by reference, teaches a
membrane process for separating carbon dioxide from a gas stream.
U.S. Pat. No. 4,589,896 to Chen et al, the contents of which are
fully incorporated herein by reference, discloses the use of a
membrane process for separation of CO.sub.2 and H.sub.2S from a
sour gas stream. One embodiment of the present invention uses a
membrane process such as that taught by Daus and Chen et al to
separate CO.sub.2, H.sub.2S, He, Ar, N.sub.2, hydrocarbon vapors
and/or H.sub.2O from a gaseous component of the recovered fluids
from the borehole: Perry's Chemical Engineers' Handbook, 7.sup.th
Ed., by Robert H. Perry and Don W. Green, 1997, Chapter 22,
Membrane Separation Processes, page 22-61, Gas-Separation Processes
the contents of which are incorporated herein by reference, teaches
further methods for accomplishing such separation.
[0075] U.S. Pat. No. 5,983,663 to Sterner , the contents of which
are fully incorporated herein by reference, discloses a
fractionation process for separation of of CO.sub.2 and H.sub.2S
from a gas stream. One embodiment of the invention uses a
fractionation process to separate CO.sub.2 and H.sub.2S from the
recovered formation fluids.
[0076] Another embodiment of the invention uses a solvent method
for removing H.sub.2S from the recovered formation fluids using a
method such as that taught by Minkkinen et al in U.S. Pat. No.
5,735,936, the contents of which are incorporated herein by
reference.
[0077] Cryogenic separation may also be used to separate carbon
dioxide and other acid gases from the recovered formation fluids.
Examples of such methods are disclosed in Swallow (U.S. Pat. No.
4,441,900) and in Valencia et al (U.S. Pat. No. 4,923,493) the
contents of which are fully incorporated herein by reference. Those
versed in the art would recognize that removal of carbon dioxide
from the recovered formation fluids is particularly important if,
as discussed above with reference to FIG. 6a, CO.sub.2 injection is
used in conjunction with electrohydraulic stimulation.
[0078] Another embodiment of the invention uses a process of
cryogenic separation such as that taught by Wissoliki (U.S. Pat.
No. 6,131,407), the contents of which are fully incorporated here
by reference, for recovering argon, oxygen and nitrogen from a
natural gas stream. Optionally, Helium may be recovered from a
natural gas stream using a cryogenic separation such as that taught
by Blackwell et al (U.S. Pat. No. 3,599,438), the contents of which
are incorporated herein by reference. In another embodiment of the
invention, a combination of cryogenic separation and solvent
extraction, such as that disclosed in Mehra (U.S. Pat. No.
5,224,350) may be used for recovery of Helium.
[0079] As discussed above, a heavy liquid portion of the recovered
formation fluids may include vanadium, nickel, sulphur and
asphaltenes. In an alternate embodiment of the present invention,
these may be recovered by using, for example, the method taught by
UedaI et al (U.S. Pat. No. 3,936,371), the contents of which are
incorporated herein by reference. The process disclosed in Ueda
includes bringing the liquid hydrocarbon in contact with a red mud
containing alumina, silica and ferric oxide at elevated
temperatures in the presence of hydrogen. Another method for
recovery of heavy metals disclosed by Cha et al (U.S. Pat. No.
5,041,209) includes mixing the heavy crude oil with tar sand,
heating the mixture to about 800.degree. F. and separating the tar
send from the light oils formed during the heating. The heavy
metals are then removed from the tar sand by pyrolysis.
[0080] While the foregoing disclosure is directed to the preferred
embodiments of the invention, various modifications will be
apparent to those skilled in the art. It is intended that all
variations within the scope and spirit of the appended claims be
embraced by the foregoing disclosure.
* * * * *