U.S. patent application number 15/243312 was filed with the patent office on 2018-02-22 for using radio waves to fracture rocks in a hydrocarbon reservoir.
The applicant listed for this patent is Saudi Arabian Oil Company. Invention is credited to Jinhong Chen, Lorne Arthur Davis, JR., Daniel T. Georgi, Hui-Hai Liu.
Application Number | 20180051546 15/243312 |
Document ID | / |
Family ID | 59702881 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180051546 |
Kind Code |
A1 |
Chen; Jinhong ; et
al. |
February 22, 2018 |
USING RADIO WAVES TO FRACTURE ROCKS IN A HYDROCARBON RESERVOIR
Abstract
The present disclosure describes methods and systems for
fracturing geological formations in a hydrocarbon reservoir. One
method includes forming a borehole in a hydrocarbon reservoir from
a surface of the hydrocarbon reservoir extending downward into the
hydrocarbon reservoir; transmitting an electromagnetic (EM) wave
through the borehole: directing at least a portion of the EM wave
to rocks at a location below the surface in the hydrocarbon
reservoir; and fracturing the rocks at the location below the
surface in the hydrocarbon reservoir by irradiating the rocks
around the borehole using at least the portion of the EM wave,
wherein irradiating the rocks elevates pore-water pressure in the
rocks causing fracturing of the rocks.
Inventors: |
Chen; Jinhong; (Katy,
TX) ; Georgi; Daniel T.; (Houston, TX) ; Liu;
Hui-Hai; (Katy, TX) ; Davis, JR.; Lorne Arthur;
(Seguin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
|
SA |
|
|
Family ID: |
59702881 |
Appl. No.: |
15/243312 |
Filed: |
August 22, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 49/00 20130101;
E21B 43/26 20130101 |
International
Class: |
E21B 43/26 20060101
E21B043/26; E21B 49/00 20060101 E21B049/00 |
Claims
1. A method, comprising: forming a borehole pattern in a
hydrocarbon reservoir from a surface of the hydrocarbon reservoir
extending downward into the hydrocarbon reservoir, wherein the
borehole pattern comprises a plurality of boreholes and the
plurality of boreholes are formed in a horizontal well pattern, and
wherein forming the borehole pattern comprises: determining a
fracturing radius based on a diameter of at least one borehole of
the plurality of boreholes and a stimulated fracture density; and
positioning the plurality of boreholes in the borehole pattern
based on the fracturing radius; and for each of the plurality of
boreholes: transmitting an electromagnetic (EM) wave through the
respective borehole: directing at least a portion of the EM wave to
rocks at a location below the surface in the hydrocarbon reservoir;
and fracturing the rocks at the location below the surface in the
hydrocarbon reservoir by irradiating the rocks around the
respective borehole using at least the portion of the EM wave,
wherein irradiating the rocks elevates pore-water pressure in the
rocks causing fracturing of the rocks.
2-5. (canceled)
6. The method of claim 1, wherein the borehole pattern is a 5-spot
pattern.
7. The method of claim 1, wherein the EM wave has a frequency
between 500 KHz and 5 MHz.
8. The method of claim 1, wherein the rocks have a permeability
between about 1 nanodarcy (nD) and 0.01 millidarcy (mD).
9. The method of claim 1, further comprising: positioning an EM
wave transmitter at a surface of the hydrocarbon reservoir; and
generating the EM wave using the EM wave transmitter.
10. The method of claim 1, further comprising: positioning an EM
wave transmitter in at least one borehole of the plurality of
boreholes, wherein the EM wave transmitter is enclosed in a
protective case; generating the EM wave using the EM wave
transmitter; and retrieving the EM wave transmitter after the rocks
are fractured.
11. The method of claim 1, wherein the location is a first location
and the EM wave is a first EM wave, further comprising:
transmitting a second EM wave through at least one borehole of the
plurality of boreholes; directing at least a portion of the second
EM wave to rocks at a second location below the surface in the
hydrocarbon reservoir; and fracturing the rocks at the second
location below the surface in the hydrocarbon reservoir by
irradiating the rocks around the at least one borehole of the
plurality of boreholes using at least the portion of the second EM
wave, wherein irradiating the rocks elevates pore-water pressure in
the rocks causing fracturing of the rocks, and a distance between
the first location and the second location is determined based on a
penetration depth of the first EM wave.
12. A method, comprising: forming a borehole pattern comprising a
plurality of boreholes in a hydrocarbon reservoir from a surface of
the hydrocarbon reservoir extending downward into the hydrocarbon
reservoir, wherein forming the borehole pattern comprises:
determining a fracturing radius based on a diameter of at least one
borehole of the plurality of boreholes and a stimulated fracture
density; and positioning the plurality of boreholes in the borehole
pattern based on the fracturing radius; transmitting an EM wave
through at least one of the plurality of boreholes; and for each of
the at least one of the plurality of boreholes, fracturing rocks
around the respective borehole using the EM wave.
13. The method of claim 12, wherein the plurality of boreholes are
formed in a vertical well pattern.
14. The method of claim 12, wherein the plurality of boreholes are
formed in a horizontal well pattern.
15. The method of claim 12, wherein an azimuthal coverage of a
stimulation zone generated by the EM wave for each of the plurality
of boreholes is a fraction of a circumference of the respective
borehole.
16. The method of claim 15, wherein a radiation pattern generated
by the EM wave for each of the at least one of the plurality of
boreholes is azimuthally asymmetric with respect to the respective
borehole.
17. The method of claim 12, wherein the plurality of boreholes are
positioned in a pattern having an equal distance between
neighboring boreholes, wherein the equal distance is determined
based on a stimulated fracture density.
18. The method of claim 12, further comprising: positioning an EM
wave transmitter at a surface of the hydrocarbon reservoir; and
generating the EM wave using the EM wave transmitter.
19. The method of claim 12, further comprising: positioning an EM
wave transmitter in at least one of the plurality of the boreholes,
wherein the EM wave transmitter is enclosed in a protective case;
generating the EM wave using the EM wave transmitter; and
retrieving the EM wave transmitter after the rocks are
fractured.
20. (canceled)
21. The method of claim 1, wherein an azimuthal coverage of a
stimulation zone generated by the EM wave for each of the plurality
of boreholes is a fraction of a circumference of the respective
borehole.
22. The method of claim 1, wherein a radiation pattern generated by
the EM wave for each of the plurality of boreholes is azimuthally
asymmetric with respect to the respective borehole.
23. The method of claim 12, wherein the borehole pattern is a
5-spot pattern.
24. The method of claim 12, wherein the EM wave has a frequency
between 500 KHz and 5 MHz.
Description
TECHNICAL FIELD
[0001] This disclosure relates to fracturing geological formations
in a hydrocarbon reservoir, for example, using electromagnetic
waves.
BACKGROUND
[0002] In some cases, a reservoir may have a tight geologic
formation. The tight geologic formation can include rocks with a
low permeability. Flows of hydrocarbon fluids can be limited in
regions where the rocks have a tight formation. It may be difficult
to recover the hydrocarbon products in these types of
reservoirs.
[0003] In some cases, hydraulic fracture techniques can be used to
fracture a tight geologic formation. In a hydraulic fracture
method, large quantity of hydraulic fluid can be pumped underground
to fracture the rocks and to keep open the fractured rocks. The
hydraulic fluid can include a mixture of water, proppants (for
example, sand or other proppants), and chemicals.
SUMMARY
[0004] The present disclosure describes methods and systems for
using radio waves to fracture rocks in a reservoir. One method
includes forming a borehole in a hydrocarbon reservoir from a
surface of the hydrocarbon reservoir extending downward into the
hydrocarbon reservoir; transmitting an electromagnetic (EM) wave
through the borehole: directing at least a portion of the EM wave
to rocks at a location below the surface in the hydrocarbon
reservoir; and fracturing the rocks at the location below the
surface in the hydrocarbon reservoir by irradiating the rocks
around the borehole using at least the portion of the EM wave,
wherein irradiating the rocks elevates pore-water pressure in the
rocks causing fracturing of the rocks.
[0005] The foregoing and other implementations can each,
optionally, include one or more of the following features, alone or
in combination:
[0006] A first aspect, combinable with the general implementation,
wherein the borehole is a first borehole, and wherein the method
further comprises forming, in the hydrocarbon reservoir, a borehole
pattern comprising a plurality of boreholes including the first
borehole; and for each of the plurality of boreholes, fracturing
rocks around the borehole using the radio wave that elevates
pore-water pressure in the rocks.
[0007] A second aspect, combinable with any of the previous
aspects, wherein the plurality of boreholes are formed in a
vertical well pattern.
[0008] A third aspect, combinable with any of the previous aspects,
wherein the plurality of boreholes are formed in a horizontal well
pattern.
[0009] A fourth aspect, combinable with any of the previous
aspects, wherein forming, in the hydrocarbon reservoir, the
borehole pattern comprising: determining a fracturing radius based
on a diameter of the borehole and a stimulated fracture density;
and positioning the plurality of boreholes in the borehole pattern
based on the fracturing radius.
[0010] A fifth aspect, combinable with any of the previous aspects,
wherein the borehole pattern is a 5-spot pattern.
[0011] A sixth aspect, combinable with any of the previous aspects,
wherein the radio wave has a frequency between 500 KHz and 5
MHz.
[0012] A seventh aspect, combinable with any of the previous
aspects, wherein the rocks have a permeability between about 1
nanodarcy (nD) and 0.01 millidarcy (mD).
[0013] An eighth aspect, combinable with any of the previous
aspects, wherein the method further comprises: positioning an EM
wave transmitter at a surface of the reservoir; and generating the
EM wave using the EM wave transmitter.
[0014] A ninth aspect, combinable with any of the previous aspects,
wherein the method further comprises: positioning an EM wave
transmitter in the borehole, wherein the EM wave transmitter is
enclosed in a protective case; generating the EM wave using the EM
wave transmitter; and retrieving the EM wave transmitter after the
rocks are fractured.
[0015] A tenth aspect, combinable with any of the previous aspects,
wherein the location is a first location and the EM wave is a first
EM wave. The method further comprises: transmitting a second EM
wave through the borehole; directing at least a portion of the
second EM wave to rocks at a second location below the surface in
the hydrocarbon reservoir; and fracturing the rocks at the second
location below the surface in the hydrocarbon reservoir by
irradiating the rocks around the borehole using at least the
portion of the second EM wave, wherein irradiating the rocks
elevates pore-water pressure in the rocks causing fracturing of the
rocks, and a distance between the first location and the second
location is determined based on a penetration depth of the first EM
wave.
[0016] Another method includes forming a borehole pattern
comprising a plurality of boreholes in a hydrocarbon reservoir from
a surface of the hydrocarbon reservoir extending downward into the
hydrocarbon reservoir; transmitting an EM wave through at least one
of the plurality of boreholes; and for each of the at least one of
the plurality of boreholes, fracturing rocks around the respective
borehole using the EM wave.
[0017] The foregoing and other implementations can each,
optionally, include one or more of the following features, alone or
in combination:
[0018] A first aspect, combinable with the general implementation,
wherein the plurality of boreholes are formed in a vertical well
pattern.
[0019] A second aspect, combinable with any of the previous
aspects, wherein the plurality of boreholes are formed in a
horizontal well pattern.
[0020] A third aspect, combinable with any of the previous aspects,
wherein an azimuthal coverage of a stimulation zone generated by
the EM wave for each of the plurality of boreholes is a fraction of
a circumference of the respective borehole.
[0021] A fourth aspect, combinable with any of the previous
aspects, wherein a radiation pattern generated by the EM wave for
each of the at least one of the plurality of boreholes is
azimuthally asymmetric with respect to the respective borehole.
[0022] A fifth aspect, combinable with any of the previous aspects,
wherein the method comprises: determining a distance based on a
stimulated fracture density; and positioning the plurality of
boreholes in a pattern having an equal distance between neighboring
boreholes, wherein the equal distance is set to the determined
distance.
[0023] A sixth aspect, combinable with any of the previous aspects,
wherein the method comprises: positioning an EM wave transmitter at
a surface of the reservoir; and generating the EM wave using the EM
wave transmitter.
[0024] A seventh aspect, combinable with any of the previous
aspects, wherein the method comprises: positioning an EM wave
transmitter in at least one of the plurality of the boreholes,
wherein the EM wave transmitter is enclosed in a protective case;
generating the EM wave using the EM wave transmitter; and
retrieving the EM wave transmitter after the rocks are
fractured.
[0025] Yet another method includes forming a borehole in a
hydrocarbon reservoir from a surface of the hydrocarbon reservoir
extending downward into the hydrocarbon reservoir; generating an EM
wave that fractures rocks in the hydrocarbon reservoir;
transmitting the EM wave through the borehole; and fracturing rocks
at a location below the surface in the hydrocarbon reservoir by
irradiating the rocks around the borehole using the EM wave,
wherein the rocks have a permeability between about 1 nanodarcy
(nD) nD and 0.01 millidarcy (mD) and irradiating the rocks elevates
pore-water pressure in the rocks causing fracturing of the
rocks.
[0026] Other implementations of this aspect include corresponding
systems and apparatuses.
[0027] The details of one or more implementations of the subject
matter of this disclosure are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
DESCRIPTION OF DRAWINGS
[0028] FIG. 1A is a schematic diagram that illustrates an example
well system including a vertical borehole according to an
implementation.
[0029] FIG. 1B is a schematic diagram that illustrates an example
well system including a horizontal borehole according to an
implementation.
[0030] FIG. 1C is a schematic diagram that illustrates an example
well system including an EM wave transmitter below the surface
according to an implementation.
[0031] FIG. 2A is a chart illustrating relationships between
pore-water pressure and temperature changes according to an
implementation.
[0032] FIG. 2B is a chart illustrating an example relationship
between the frequency and the penetration depth of the EM wave
according to an implementation.
[0033] FIG. 3 is a schematic diagram that illustrates volume
distributions of fractured rocks according to an
implementation.
[0034] FIG. 4A is a schematic diagram that illustrates an example
well system including multiple vertical boreholes according to an
implementation.
[0035] FIG. 4B is a schematic diagram that illustrates an example
well system including a plurality of horizontal boreholes according
to an implementation.
[0036] FIG. 4C illustrates a top view of an example pattern of
borehole formations according to an implementation.
[0037] FIG. 4D illustrates a side view of an example pattern of
borehole formations according to an implementation.
[0038] FIG. 5 illustrates an example method for fracturing rocks
using electromagnetic waves according to an implementation.
[0039] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0040] This disclosure generally describes methods and systems for
fracturing rocks in a hydrocarbon reservoir. In some cases, a
reservoir may have tight geographic formations between wells. Flows
of hydrocarbon fluids can be very limited in regions where the
rocks have a tight formation. In some cases, the rocks in the
regions of a tight formation may have a low permeability. Examples
of a low permeability can include matrix permeability between less
than 1 nanodarcy (nD) and 0.01 millidarcy (mD). Examples of rocks
having a low permeability include shales, tight sandstones, and
tight carbonates. Therefore, if a region of a reservoir has a tight
formation, it may be difficult to recover the hydrocarbon products,
for example, oil or gas, from the region. In some cases, hydraulic
fracturing can be used to fracture the rocks and improve
permeability. However, using hydraulic fracturing to recover
hydrocarbon products may have one or more disadvantages. For
example, hydraulic fracturing may use a significant amount of
water. Furthermore, the hydrocarbon recovery rate using hydraulic
fracturing can be less than 10% for oil and less than 35% for gas.
Hydraulic fracturing can also induce damage to the fracture surface
and impede flow from the formation to the fractures. Moreover, it
may be difficult to control the location of the fracturing zone. In
addition, the recovered fluid from hydraulic fracturing may create
environment issues and thus may need to be disposed of or
treated.
[0041] In some cases, heat transfer can be used to increase the
fluidity of the oil in geological formations with a high
permeability. In one example, microwave can be used to increase the
temperature of the wellbore or a heating device in a well. Because
microwave has a high intensity, the temperature of the wellbore or
the heating device can be raised to a high level, for example, to a
level as high as 700 F. The heat can be transferred from the
wellbore or the heating device to the oil in the subterranean
formation around the well. The heat can break down the chemical
structure of the oil and decrease the viscosity of the oil. If the
subterranean formation has a high permeability, for example, if the
rocks around the well have a loose formation, this approach can
make it easier for the oil to flow from one well to another well.
However, using this approach to fracture rocks with a tight
formation may have one or more issues. For example, microwave has a
short wavelength, and therefore may have a low penetration
depth.
[0042] In a subterranean structure with a tight geological
formation, pore-water pressure can increase rapidly when the
pore-water in the rocks is heated. In the context of this
disclosure, pore-water pressure refers to the pressure of connate
water held in gaps between particles within a soil or rock. In some
cases, rocks in a tight formation can be fractured by increasing
the pore-water pressure. In some implementations, electromagnetic
(EM) waves with long wavelength can be used to irradiate directly
on the rocks around a borehole. Examples of the EM waves with long
wavelength can include a radio wave. In some cases, radio waves
having a frequency between 500 kilohertz (KHz) to 5 megahertz (MHz)
can be used to irradiate the rocks and heat the pore water in the
rocks. When the water temperature is increased to a sufficiently
high level, the pore-water pressure can fracture the rocks.
Alternatively or additionally, EM waves with even higher frequency,
for example, up to 100 MHz, can be used to irradiate the rocks.
[0043] In some cases, this approach can provide a mechanism to
fracture rocks without using fracturing fluids. The mechanism can
increase rock permeability in the tight formation and increase
recovery rate in the reservoir. In addition, this approach can
introduce minimum formation damages by redistributing the fractured
rocks in the borehole. Furthermore, patterns of the boreholes can
be selected to optimize the size of the total stimulation zone, and
thus the size of the stimulated zone can be well controlled.
Moreover, this approach can work in deep reservoir with strong
rocks, for which hydraulic fracturing may not be practical. In
addition, this approach does not introduce chemicals in the process
and therefore can be more environmental friendly.
[0044] FIGS. 1A and 1B are schematic diagrams that illustrate
example well systems 102 and 104, respectively, according to
respective implementations. The example well systems 102 and 104
can use EM waves to irradiate rocks and fracture rocks around a
wellbore, as described below.
[0045] In some cases, changes in the pore-water pressure can depend
on the water content, rock matrix modulus, temperature changes, or
a combination thereof, in the reservoir rocks. FIG. 2A is a chart
210 illustrating relationships between pore-water pressure and
temperature changes, according to an implementation. In some cases,
the rocks can be fractured if the pore-water pressure is equal to,
or larger than, a summation of the minimum in-situ effective stress
and the rock tensile strength of the rocks. In some cases, for
rocks from tight formations, rocks may be fractured when pore-water
pressure reaches a few thousand pounds per square inch (psi). The
chart 210 shows the pore-water pressure elevations for 10% water in
the rocks with different matrix modulus. As shown in FIG. 2A, if
the temperature is increased by 20 degrees Celcius, the pore-water
pressure can be increased to about 10,000 psi or higher. In these
cases, the increase of the pore-water pressure may pulverize the
rocks into small fragments, and thus fracture the rocks and
increase the permeability.
[0046] In some cases, the penetration depth of an EM wave into a
rock formation can be a function of the wavelength of the EM wave
and the dielectric property of the rock formation. Microwave has a
wavelength of approximately 12 cm, and thus may not be used to
efficiently stimulate formations much more beyond 12 cm. On the
other hand, EM waves with longer wavelength than microwaves, for
example, radio waves, can provide much longer penetration depth
than microwaves. For example, radio waves having frequency in the
MHz range can penetrate several dozen feet from a borehole into the
rocks around the borehole, and thus stimulate a much larger volume
of tight rocks for production in a single well.
[0047] In some cases, the average power generated from an EM wave
can be represented in the equation (1):
P av = 1 2 .omega. 0 i .intg. V r , i '' E E * dV ( 1 )
##EQU00001##
[0048] where P.sub.av represents the average power, w represents
the EM frequency, E represents the electric field strength, E*
represents the conjugate of E, .epsilon.''.sub.r,i represents the
relative dielectric loss of the ith mineral composition including
the fluids, and .epsilon..sub.0 represents a constant coefficient
that is equal to 8.85.times.10.sup.-12 F/m.
[0049] As shown in equation (1), the average power can be
calculated by integrating over the volume the EM wave irradiates.
The volume of that the EM wave irradiates depends on the
penetration depth of the EM wave. Equation (2) represents an
example calculation of the penetration depth:
D = .lamda. 2 .pi. { 2 r ' [ 1 + ( r '' / r ' ) 2 ] 1 / 2 - 1 } - 1
/ 2 ( 2 ) ##EQU00002##
[0050] where D represents the penetration depth, .lamda. represents
the wavelength of the EM wave, .sub.i' and .epsilon..sub.r''
represent the average relative dielectric constant and dielectric
loss of the rock formation, respectively. The term
.epsilon..sub.r'' can be a function of the dielectric loss
.epsilon..sub.dl'' and the conductivity .sigma., which can be
represented as .sigma.=1/.rho., where .rho. represents the
formation resistivity. Equation (3) represents an example
calculation of the dielectric loss .epsilon..sub.r'':
'' = dl '' + .sigma. 2 .pi. v 0 ( 3 ) ##EQU00003##
[0051] where v represents the EM frequency and v=c/.lamda.,
c=3.times.10.sup.8 m/s, and .epsilon..sub.0=8.854.times.10.sup.-12
F/m.
[0052] FIG. 2B is a chart 220 illustrating an example relationship
between the frequency and the penetration depth of the EM wave
according to an implementation. In the illustrate example,
.epsilon..sub.i' is set to 4 and .epsilon..sub.dl'' is set to 0.3.
The chart 220 illustrates the peneration depth as a function of the
EM wave frequency for different resistivities of the formation. The
resisitivity of a production shale formation can be between 100
.OMEGA.m and 1000 .OMEGA.m. Therefore, using an EM wave in the
range of 500 KHz to 5 MHz can provide a peneration depth of several
feet. Alternatively or additionally, EM waves with higher
frequency, for example, up to 100 MHz, can be used to irradiate the
rocks
[0053] As shown in equation (2) and FIG. 2B, the penetration depth
depends on the wavelength of the EM wave and the property of the
rock formation. In the context of the present disclosure, a
stimulation zone refers to the region of rocks that are affected by
the EM wave. In some cases, the depth of the stimulation zone can
be larger than the penetration depth due to the thermal
conductivity. In some implementations, the depth of the stimulated
zone can be a few dozens of feet. As shown in Eq. (1), the heating
efficiency of the formation can depend on the square of the field
intensity E of the EM wave.
[0054] Returning to FIG. 1A, the example well system 102 includes a
wellbore 114 below the terranean surface 110. The wellbore 114 is
extended by a vertical borehole 116 in the tight rock formation
region 120. The tight rock formation can span a single formation,
portions of a formation or multiple formations.
[0055] The well system 102 also includes an EM wave transmitter
112. The EM wave transmitter 112 can be implemented as one or more
hardware circuit elements, software, or a combination thereof that
can be configured to generate an EM wave. In some implementations,
an EM wave transmitter, for example, the EM wave transmitter 112,
can include a power supply, an oscillator, a modulator, a power
amplifier, or any combinations thereof, that can be configured to
generate EM waves to irradiate the rock formation. In some
implementations, the transmitter can include a synthesized radio
frequency (RF) signal generator, a free running RF signal
generator, or a combination thereof
[0056] The well system 102 also includes an antenna 115. The
antenna 115 can be positioned in the vertical borehole 116. The
antenna 115 can be configured to transmit radio waves into in the
tight rock formation surrounding the vertical borehole 116. The
antenna 115 can be implemented using dipole antenna.
[0057] The well system 102 also includes a transmission line 118
that is coupled with the EM wave transmitter 112 and the antenna
115. The transmission line can be configured to direct the EM wave
generated by the EM wave transmitter 112 to the antenna 115. The
transmission line 118 can be implemented using a coaxial cable, a
twisted pair wire, or a waveguide. In some implementations, a
waveguide can be implemented using hollow conductive metal
pipes.
[0058] In operation, the EM wave transmitter 112 generates EM
waves. The EM waves can travel through the transmission line 118 to
the antenna 115. The antenna 115 irradiates EM waves to the rocks
around the vertical borehole 116. The irradiation raises the
temperature of the water and rocks around the vertical borehole 116
and increases the pore-water pressure in the rocks. The increased
pore-water pressure fractures the rocks. The fractured rocks around
the vertical borehole 116 can become loose. Some of the loosed
rocks can collapse into the vertical borehole 116. Rocks collapsing
into the vertical borehole 116 can cause restructuring of the rocks
and create a corresponding increase in the permeability of the
rocks. The hydrocarbon products, for example, oil or gas, in the
tight rock formation region 120 can then be recovered through the
wellbore 114.
[0059] In some cases, a horizontal borehole can be used instead of
the vertical borehole. As shown in FIG. 1B, the example well system
104 includes a wellbore 134 below the terranean surface 130. The
wellbore 134 is extended by a horizontal borehole 136 in the tight
rock formation region 140. The well system 104 also includes an EM
wave transmitter 132, a transmission line 138, and an antenna
135.
[0060] In operation, the EM wave transmitter 132 generates EM waves
that travel through the transmission line 138 to the antenna 135.
The antenna 135 irradiates EM waves to the rocks around the
horizontal borehole 136. The irradiation raises the temperature of
the rocks around the horizontal borehole 136 and increases the
pore-water pressure in the rocks around the horizontal borehole
136. In some cases, the irradiation is targeted to the stimulation
zone above the horizontal borehole 136. The increased pore-water
pressure fractures the rocks. The fractured rocks can become loose.
Some of the loosed rocks can collapse into the horizontal borehole
136. Rocks collapsing into the horizontal borehole 136 can cause
restructuring of the rocks and creates a corresponding increase in
the permeability of the rocks. The hydrocarbon products, for
example, oil or gas, in the tight rock formation region 140 can
then be recovered through the wellbore 134.
[0061] In some cases, as illustrated in FIG. 1A and 1B, the EM wave
transmitter can be positioned at the surface. Alternatively or in
combination, the EM wave transmitter can be positioned inside the
borehole. FIG. 1C is a schematic diagram that illustrates an
example well system 106 including an EM wave transmitter below the
surface according to an implementation. As shown in FIG. 1C, the EM
wave transmitter 112 is placed inside the vertical borehole 116 in
the tight rock formation region 120. In some cases, a case 160 can
be used to protect the EM wave transmitter 112, the transmission
line 118, the antenna 115, or any combinations thereof, from the
collapsed rocks. The case 160 can be implemented using a ceramic
conduit. In some cases, a cable 162 can be used to retrieve the
case 160 after the rocks are irradiated and fractured to reuse the
components protected by the case 160.
[0062] In some cases, the irradiation can be performed in stages.
For example, in a first stage irradiation, the antenna 115 can be
positioned at a first location 172. The antenna 115 can irradiate
rocks surrounding the first location 172. After the first stage
irradiation, the antenna 115 can be repositioned at a second
location 174 to irradiate the rocks around the second location 172.
The distance between the first location 172 and the second 174 can
be determined based on the penetration depth of the EM waves, as
discussed previously in FIG. 2B and associated descriptions. This
process can be repeated for additional stages of irradiation.
[0063] FIG. 3 is a schematic diagram 300 that illustrates volume
distributions due to EM wave irradiation, according to an
implementation. The schematic diagram 300 includes a illustration
of stimulation zones 310 and 320, respectively. The stimulation
zone 310 represents the formation before the irradiation. As shown
in FIG. 3, the stimulation zone 310 includes a borehole 312 that is
drilled into the stimulation zone 310. In the illustrated example,
the stimulation zone 310 has a length L and a radius R. The
borehole 312 has a radius r. As discussed previously, during
irradation, while the radio wave travels through the borehole 312,
the radio wave irradiates the rocks around borehole 312, which
includes the rocks in the stimulation zone 310. The stimulation
zone 320 represents the formation after the irradiation. The
stimulation zone 320 has the same length L and the same radius R as
the stimulation zone 310. After irradiation, the fractured rocks in
the stimulation zone 310 fall into the borehole 312 due to
gravity.
[0064] Assuming the fractures are homogeneously distributed in the
stimulated zone 320 and the stimulated fracture density is a (the
fraction of fracture volume over the stimulated volume), equation
(3) represents the volume redistributions in the stimulation zones
310 and 320 by the fractured rocks:
.pi.r.sup.2L=.alpha..pi.R.sup.2L Or R=d/(2 {right arrow over
(.alpha.)}) (3)
[0065] where d represents the diameter of the borehole 312 and
d=2r. In some cases, when the stimulated fracture density .alpha.
is 0.1%, the permeability can increase approximately 3 orders of
magnitude. This would significantly enhance hydrocarbon production
in rocks with tight formations. In some cases, for a 6 inch
borehole, the radius of the stimulated zone can be approximately 8
ft. For a 24 inch borehole, the radius of the stimulated zone can
be extended to more than 60 ft. Furthermore, if there is any
original void space in the formation other than the drilled
borehole, the stimulated zone or the fracture density can be
further increased. To use the EM energy for stimulation
efficiently, the penetration depth D of the EM in Eq. (2) can be
optimized to approximately equal to the stimulated zone size R in
Eq. (3). In some cases, the size of the borehole can be determined
based on a target radius of the stimulation zone and a targetted
stimulated fracture density using equation (3).
[0066] When the borehole is positioned horizontally, the gravity
and the elevated pore-water pressure can redistribute the rock
fragments into the horizontal borehole. In some cases, it may be
beneficial to fracture a portion of the formation above the
borehole, and therefore the rocks above the borehole can be
redistributed into the borehole under gravity. For example, instead
of transmitting the EM wave in an omni-direction orientation, the
antenna 135 can be configured to transmit EM waves above the
horizontal borehole 136. Therefore, the azimuthal coverage of the
stimulation zone can include a fraction of the circumference of the
horizontal borehole 136.
[0067] In some cases, the stimulated zone can be significantly
increased by using multiple boreholes. This approach may increase
efficiency because drilling multiple sidetrack wells can be
relatively cheap. For example, the patterned boreholes can be
drilled using sidetracking and can share one vertical wellbore.
[0068] FIGS. 4A and 4B are schematic diagrams that illustrate
example well systems 402 and 404, respectively, according to an
implementation. The example well systems 402 and 404 can include
multiple boreholes. As shown in FIG. 4A, the example well system
402 includes a wellbore 414 below the terranean surface 410. The
wellbore 414 is extended by multiple vertical boreholes 416a-e in
the tight rock formation region 420. The well system 402 also
includes an EM wave transmitter 412 and transmission lines 418a-e
that connect the EM wave transmitter 412 with antennas 415a-e,
respectively. In operation, the EM wave transmitter 412 generates
EM waves that are directed through each of the multiple boreholes
416a-e to the antennas 415a-e using the transmission lines 418a-e.
The antennas 415a-e transmit the EM waves to irradiate the rocks
around the boreholes 416a-e and fracture the rocks around the
boreholes 416a-e with increased pore-water pressure.
[0069] In some cases, the multiple boreholes 416a-e can form a
pattern. In some implementations, the pattern can be selected to
optimize the size of the total stimulation zone for a given number
of boreholes. For example, a 5-spot pattern can be selected to
position the multiple boreholes 416a-e. In a 5-spot pattern, the
distances between a central borehole, for example, the borehole
416c, and each of the surrounding boreholes, for example, the
boreholes 416a, 416b, 416d, and 416e are the same. As discussed
previously, the radius of the stimulation zone introduced by one
borehole can be determined based on the stimulated fracture density
and penetration depth of the EM wave. Therefore, the distance
between the central borehole and a surrounding borehole can be
determined based on the radius of the stimulation zone. For
example, the distance between the central borehole and a
surrounding borehole can be set to 2 times the determined radius.
Thus, the size of the total simulation zone can be optimized if the
size of the borehole pattern is set according to the calculation
described previously.
[0070] FIG. 4C illustrates a top view 450 of an example pattern of
borehole formations according to an implementation. As illustrated,
the example pattern is a 5 spot pattern, where each surrounding
borehole is positioned with the same distance relative to a central
borehole. This pattern can provide an optimized coverage because
the pattern covers a large stimulated zone with a small number of
boreholes, and therefore saves drilling cost. This pattern can also
be repeated easily to cover a portion of a reservoir or the entire
reservoir.
[0071] In some cases, as discussed previously, horizontal boreholes
can be used instead of the vertical boreholes. As shown in FIG. 4B,
the example well system 404 includes a wellbore 434, below the
terranean surface 430. The wellbore 434 is extended by multiple
horizontal boreholes 436a-c in the tight rock formation region 440.
The well system 404 also includes an EM wave transmitter 432 and
transmission lines 438a-c that connect the EM wave transmitter 432
with antennas 435a-c, respectively. In operation, the EM wave
transmitter 432 generates EM waves that are directed through each
of the multiple boreholes 436a-c, using the transmission lines
438a-c. The antennas 435a-c transmit the EM waves to irradiate the
rocks around the boreholes 436a-c and fracture the rocks around the
boreholes 436 with increased pore-water pressure.
[0072] In some cases, a pattern of equal distance between
neighboring boreholes can be selected. In some cases, the fractured
rocks above a horizontal borehole are redistributed into the
horizontal boreholes. In these or other cases, the distance between
the boreholes can be set close to the determined radius. FIG. 4D
illustrates a side view 460 of an example pattern of borehole
formations according to an implementation. The side view 460
includes multiple horizontal boreholes 462. For each horizontal
borehole 462, the EM waves can be targeted to the rocks above the
horizontal borehole 462. The rocks in regions 464 above the
horizontal borehole 462 are redistributed during fracturing. The
distances between neighboring horizontal boreholes 462 are set to
R, which is the radius of the stimulation zone.
[0073] As discussed previously, the horizontal borehole can be
tilted towards a fracture direction to generate a radiation pattern
that is azimuthally asymmetric with respect to the borehole. For
example, the horizontal borehole may be tilted by an angle relative
to the vertical wellbore. Consequently, the size of the stimulated
zone can be represented by equation (4):
R = .pi. 2 .alpha..theta. d ( 4 ) ##EQU00004##
[0074] where .theta. represents the angle of the fractured zone
above the borehole. In some cases, 0.theta. can be set to 100 to
110 degrees.
[0075] In some cases, while multiple boreholes are formed, one or
more boreholes among the multiple boreholes are used for
irradiation. The rocks around the one or more boreholes can be
fractured by the EM waves. The remaining boreholes can be used for
future irradiation in a later stage. This approach may be more
economical than drilling boreholes in different stages. In one
example, every other borehole can be used for irradiation in the
first stage. The the high attenuation caused by the connate water
may trigger a second stage of irradiation. During the second stage,
one or more of the remaining boreholes can be used for
irradiation.
[0076] In some cases, during the first stage, the presense of the
unused boreholes can affect affect the stress distributions and
result in local stress concentrations that can deflect the EM
wave-induced fractures. In these or other cases, a temperature
survery or a Distributed temperature sensing (DTS) system can be
used to measure the temperature at locations around unused
boreholes to determine whether the EM waves have penetrated to
these locations. If the temperature does not rise to a threshold,
the EM waves have not penetrated to these locations, and
irraditions from the unused boreholes can be performed.
[0077] FIG. 5 illustrates an example method 500 for fracturing
rocks using EM waves according to an implementation. For clarity of
presentation, the description that follows generally describes
method 500 in the context of FIGS. 1A-1C, 2A-2B, 3, and 4A-4D.
[0078] At 502, a borehole is formed in a hydrocarbon reservoir. The
borehole is formed from a surface of the hydrocarbon reservoir
extending downward into the hydrocarbon reservoir. In some cases, a
borehole is a first borehole, and multiple boreholes are formed in
the hydrocarbon reservoir. The multiple boreholes include the first
borehole. In some cases, the multiple boreholes include vertical
boreholes. Alternatively or in combination, the multiple boreholes
include horizontal boreholes. In some cases, the multiple boreholes
formed a 5-spot pattern.
[0079] At 504, an EM wave that fractures rocks in the hydrocarbon
reservoir is transmitted through the borehole. In some cases, the
EM wave is generated using an EM wave transmitter. In some cases,
the EM wave transmitter can be positioned at a surface of the
reservoir. Alternatively, the EM wave transmitter can be positioned
inside the boreholes. In some cases, the EM wave transmitter is
configured to generate an EM wave having a frequency between 500
KHz and 5 MHz. Alternatively or in combination, the EM wave
transmitter can be configured to generate EM waves up to 100 MHz.
At 506, at least a portion of the EM wave is directed to rocks at a
location below the surface in the hydrocarbon reservoir. At 508,
the rocks at a location below the surface in the hydrocarbon
reservoir are fractured by irradiation of the radio wave.
[0080] This description is presented to enable any person skilled
in the art to make and use the disclosed subject matter, and is
provided in the context of one or more particular implementations.
Various modifications to the disclosed implementations will be
readily apparent to those skilled in the art, and the general
principles defined herein may be applied to other implementations
and applications without departing from scope of the disclosure.
Thus, the present disclosure is not intended to be limited to the
described and/or illustrated implementations, but is to be accorded
the widest scope consistent with the principles and features
disclosed herein.
[0081] Accordingly, the previous description of example
implementations does not define or constrain this disclosure. Other
changes, substitutions, and alterations are also possible
without
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