Rock fracturing method, and reservoir layer construction method using the same

Abstract

To suppress induced earthquakes caused by rock fracturing during drilling by pressing-in supercritical CO2 and then injecting water during well drilling.SOLUTION: A method for fracturing rock near a well using supercritical CO2 comprises: a CO2 pressing-in step of pressing-in the supercritical CO2 into the well; and a pressurized water pressing-in step of pressing-in pressurized water into the well after the pressing-in of the supercritical CO2 is stopped, and backing up the supercritical CO2 with the pressurized water.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a rock fracturing method using supercritical carbon dioxide and a reservoir creation method using the same. [Background technology]

[0002] One well drilling technology known is, for example, Patent Document 1, which was previously proposed by the present applicant. Patent Document 1 relates to a well drilling device used for drilling deep wells such as oil wells, geothermal wells, and geological exploration wells. Drilling involves injecting mud water into the ground together with a rotating drill collar 23 having a bit 24. Patent Document 2 also discloses a well structure that uses fluids such as water to perform fracturing from a drilled well. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 55-136390 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-025239 Summary of the Invention [Problem to be solved by the invention]

[0004] Fracturing using water (mud water) like this tends to increase AE energy (Acoustic Emission: a phenomenon in which strain energy accumulated inside a material is released as elastic waves when the material deforms or cracks), which poses a risk of induced earthquakes, and how to prevent this is a major issue. The applicant of this application has discovered that by injecting supercritical carbon dioxide (hereinafter referred to as supercritical CO2) and then injecting water in combination, it is possible to prevent induced earthquakes caused by rock fracturing that occurs during drilling. [Means for solving the problem]

[0005] In order to solve the above problems, the following means are provided. (1) A method for fracturing rock mass near a well using supercritical CO2, comprising: a CO injection step of injecting the supercritical CO into the well; a pressurized water injection step of injecting pressurized water into the well after stopping the injection of the supercritical CO2 and boosting the supercritical CO2 with the pressurized water; A rock crushing method comprising the steps of: (2) The rock fracturing method according to (1), wherein the pressurized water contains a chelating agent. (3) The rock breaking method according to (2), wherein the chelating agent is a biodegradable chelating agent. (4) The rock breaking method according to (2), wherein the chelating agent is glutamic acid diacetate tetrasodium. (5) The rock fracturing method according to (2), wherein the pressurized water is acidic. (6) The rock fracturing method according to (2), wherein the pressurized water further contains hydrogen fluoride. (7) The rock crushing method according to (2), wherein the pressurized water further contains a thickener. (8) A rock fracturing method according to any one of (1) to (7), wherein the CO2 injection step comprises a first CO2 injection step of injecting supercritical CO2 at a first flow rate under a first pressure, and a second CO2 injection step, which is a step carried out after the first CO2 injection step, of injecting supercritical CO2 at a second pressure lower than the first pressure under a flow rate higher than the first flow rate. (9) A rock breaking method according to any one of (1) to (7), characterized in that after the pushing step with pressurized water, it includes a pressurized water removal step of flowing water into the crack to wash away the pressurized water, and / or flowing the pressurized water back out of the crack to recover it. (10) Using the rock crushing method according to any one of (1) to (7), A reservoir creation method for creating a reservoir in the vicinity of the well. [Effects of the Invention]

[0006] By adopting the above method, it is possible to suppress induced earthquakes caused by rock fracturing during well drilling. It is also possible to create a reservoir near the well, which is expected to have benefits such as efficient recovery of geothermal energy. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of a simulation device 1 used to verify a borehole rock fracturing method using supercritical CO2 and subsequent boosting water using a core according to the present invention. [Figure 2] Figure 2(a)(b) is a graph comparing the hydraulic fracturing and supercritical CO2 fracturing conditions of a core sample (Komatsu andesite). [Figure 3] Figures 3(a) and (b) show the results of verification of fracturing due to water pressure after supercritical CO2 injection. Figure 3(a) is a graph corresponding to Figures 2(a) and (b), and Figure 3(b) is an X-ray CT image of core sample 2. [Figure 4] Figure 4 is a schematic diagram conceptualizing the destruction mechanism. [Figure 5] FIG. 5 is a conceptual diagram of an embodiment of the method for fracturing rock mass in a well using supercritical CO2 and subsequent boosting water according to the present invention. [Figure 6] FIG. 6 is a schematic diagram of the apparatus used in the chelating agent-containing water flow experiment. [Figure 7] FIG. 7 is a graph showing the results of measuring the permeability in an experiment in which water containing a chelating agent was passed through the system. [Figure 8] FIG. 8 is an image showing the results of pore analysis in a chelating agent-containing water flow experiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The rock fracturing method and reservoir creation method using supercritical CO2 according to the present invention will be described below. The rock fracturing method of this embodiment is a method for fracturing rock near a borehole using supercritical CO2, and includes the steps of injecting supercritical CO2 into the borehole, and, after the injection of supercritical CO2 is stopped, injecting pressurized water into the borehole and backing up the supercritical CO2 with the pressurized water. Hydraulic fracturing has been known as a rock fracturing method for some time, but hydraulic fracturing involves high fracturing pressure and releases large amounts of AE energy, which poses a risk of induced earthquakes. Another known method of fracturing rock is the use of supercritical CO2. Compared to hydraulic fracturing, supercritical CO2 fracturing requires less fracturing pressure and can reduce the risk of induced earthquakes, but the cracks and openings in the rock tend to be smaller, and the use of a large amount of supercritical CO2 makes it expensive. In contrast, the rock fracturing method of this embodiment comprises the steps of injecting supercritical CO2 into a borehole, and, after stopping the injection of supercritical CO2, injecting pressurized water into the borehole and backing up the supercritical CO2 with the pressurized water. This allows the fracturing pressure to be kept low, just like with supercritical CO2 alone, and the release of AE energy to be kept low compared to hydraulic fracturing, making it possible to reduce the energy used during fracturing and to lower the risk of induced earthquakes due to stimulation of earthquake faults. In addition, the pressurized water used for boosting the rock can widen the cracks and openings, improving permeability in the same way as hydraulic fracturing. Furthermore, improved economic efficiency can be expected due to the reduction in the amount of supercritical CO2 used. Furthermore, by adding a chelating agent to the pressurized water used for boosting, it is possible to dissolve the minerals in the cracks or in the cracks and around the cracks, resulting in a greater fracturing effect than when water without a chelating agent is used. It is desirable that the water containing the chelating agent be moderately thickened to prevent the agent from dissipating outside the cracks. Specifically, it is preferable to add a thickener to the water containing the chelating agent. Although not particularly limited, for example, scleroglucan, a thickening polysaccharide derived from microorganisms, can be used. Furthermore, the mineral dissolution-promoting effect of water containing the chelating agent is exhibited over a wide range of pH levels, but acidic conditions are preferred because the promoting effect is greater at acidic pH levels. Furthermore, water containing the chelating agent has a greater mineral dissolution-promoting effect when it contains an appropriate amount of hydrogen fluoride (this is because the chelating agent promotes the dissolution of metal elements and the hydrogen fluoride promotes the dissolution of silicon). The hydrogen fluoride source is not particularly limited, but NH4HF2 can be used from the perspective of environmental and safety considerations. It is also preferable to have a pressurized water removal step after the step of pushing with pressurized water, in which water is flowed into the inside of the crack to wash out the pressurized water and / or the pressurized water is flowed back from the crack to be recovered. Furthermore, by using this rock fracturing method, it becomes possible to create a reservoir near the well, which makes it possible to create a reservoir near the well and efficiently recover geothermal energy, for example. Furthermore, if the reservoir is a geothermal reservoir, by storing supercritical CO2 in the reservoir, when supercritical CO2 is used as a heat transfer medium, the heat transfer medium can be circulated, and heat can be efficiently recovered from the geothermal reservoir, making it possible to realize highly efficient geothermal power generation.In addition, the reservoir may be for oil or natural gas extraction, or for CCS (carbon dioxide capture and storage), etc. [Example]

[0009] FIG. 1 is a diagram showing a simulation experiment example 1 for verifying a borehole rock fracturing method using supercritical CO2 and subsequent boosting water, which was used to verify a borehole rock fracturing method using a core according to the present invention and the injection of supercritical CO2 and subsequent boosting water.

[0010] In Figure 1, reference numeral 1 denotes a core-based pressure device for fracturing experiments (hereinafter simply referred to as "pressure device 1"); 2 denotes a core sample of this Komatsu andesite (30 mm diameter, 25 mm thick); 3 denotes a 10 mm deep borehole for injecting supercritical CO2 or water thereafter; 4 denotes a hand pump for pumping oil; 5 denotes a hydraulic jack for pressurizing the pressure device 1; 6 denotes a load cell for measuring load; 7 denotes a displacement transducer for measuring the displacement of the core sample 2; 8 denotes a piston for applying a compressive load to copper gaskets 9a and 9b; 9a denotes a copper gasket with a hole in the center so that fluid is injected only into the borehole 3; 9b denotes a copper gasket without a hole in the center; and 10 denotes a triaxial compression chamber for storing the core sample 2. The reference numeral 11 denotes a heater that heats the core sample 2, 12 denotes an acoustic emission (AE) sensor that measures the AE emitted from the core sample 2, 13 denotes a syringe pump that pressurizes and injects the test fluid, 14 denotes a pressure transducer that measures the pressure of the fluid injected into the borehole 3, 15 denotes a thermocouple that measures the temperature of the fluid injected into the borehole 3, and 16 denotes a syringe pump that injects molten resin at a predetermined pressure. At the top of the pressure vessel 10 are pipes for injecting the molten resin at a predetermined pressure, a pressure gauge 17, and a syringe pump 16. Reference numeral 17 denotes a pressure transducer that measures the injection pressure, 18 denotes a piston that pressurizes the molten resin, 19 denotes polyethylene resin that melts at the temperature of the experimental conditions to become an ultra-high viscosity liquid, and 20 and 21 denote thermocouples for measuring temperature.

[0011] Komatsu andesite is an andesite native to Manazuru, Kanagawa Prefecture, that was formed when lava flowed from the Hakone volcano eruption approximately 400,000 years ago, was forced into the sea and rapidly solidified. Supercritical CO2 refers to CO2 in a supercritical state, where the critical pressure exceeds 7.38 MPa and the critical temperature exceeds 31.1°C. CO2 in its supercritical state combines the solubility of liquid-like substances with the diffusibility of gas. It possesses the properties of a gas that can infiltrate anywhere (diffusibility) and the properties of a liquid that dissolves components (solubility), and is capable of continuously and dramatically changing its physical properties (https: / / www.itec-es.co.jp / efforts / pro_co2_00 / ) (https: / / shinko-airtech.com / supercritical / critical.html).

[0012] As is clear from Figure 1, the rock core sample 2 is placed horizontally in the center of a pressure vessel 10. A borehole 3 is opened to a depth of 10 mm on the fluid injection side end face of the core sample 2, and a copper gasket 9a with a hole in the center is attached so that the fluid is injected only into the borehole 3, and a copper gasket 9b without a hole is attached to the opposite end face.

[0013] A piston 8 is installed on the outside of this gasket 9b, and a compressive load is applied to the copper gaskets 9a and 9b by this piston 8, and this load (axial load) acts on the core sample 2. The core sample 2 is filled with polyethylene resin 19, which melts at the temperature of the experimental conditions to become an ultra-high viscosity liquid, and the pressure of this molten resin 19 applies a confining pressure to the core sample 2. Note that to prevent the molten resin 19, which solidifies after the experiment (after cooling), from adhering to the core sample 2, the sample surface that comes into contact with the molten resin is covered with a resin film (polyimide film) (not shown) that does not melt even at the experimental temperature.

[0014] The pressure vessel 10 containing the core sample 2 is placed in an electric furnace 11, which is installed in a loading frame that applies an axial load. An acoustic emission (AE) sensor 12 is attached to the loading frame. The piston 8 on the injection side is connected to a piping for injecting the fracturing fluid and a syringe pump 13. A pressure gauge 14 and a thermocouple 15 are attached to this piping for measuring the pressure and temperature of the fluid injected into the borehole 3. Furthermore, in order to apply a confining pressure to the core sample, a piping for injecting molten resin at a predetermined pressure, a pressure gauge 17, and a syringe pump 16 are connected to the top of the pressure vessel 10.

[0015] The experimental procedure and conditions for the experimental apparatus for verifying the method for fracturing rock mass in a well using supercritical CO2 and subsequent boosting water according to the present invention shown in Figure 1 are as follows. First, a dry rock core sample 2, which has previously undergone permeability measurements and X-ray CT imaging at room temperature and atmospheric pressure, is placed in a pressure vessel 10, and then the temperature, confining pressure, and axial stress are set to predetermined values, and AE measurement begins.

[0016] Next, the space from the pump 13 to the borehole 3 is filled with "water" or "supercritical CO2" as a fracturing fluid, and the pressure is set to 10 MPa and maintained for approximately 20 minutes. The fluid pressure is set to 10 MPa in order to liquefy the CO2 in the syringe pump 13 and inject it at a constant flow rate.

[0017] Finally, a fracturing fluid consisting of supercritical CO2 is injected at a predetermined flow rate until the pressure reaches a level at which the copper gasket 9a on the injection side end face of the core sample 2 can no longer maintain a seal. After the experiment, permeability measurements and X-ray CT images were taken for core sample 2 at room temperature and atmospheric pressure.

[0018] In the method for fracturing rock mass in a borehole using supercritical CO2 and subsequent boosting water according to this Example 1, the properties of supercritical CO2 are utilized to the maximum extent during borehole drilling, so that supercritical CO2 is permeated into the rock mass, and instead of sudden rock fracturing, fine cracks are gradually and asymptotically induced by the release of small AE energy, thereby avoiding large, sudden rock fracturing and suppressing induced earthquakes.

[0019] Using this device 1, we conducted a comparison of fracturing experiments using water and supercritical CO2 on a core sample (Komatsu andesite). Figure 2(a)(b) is a graph comparing the conditions of hydraulic fracturing and supercritical CO2 fracturing of a core sample (Komatsu andesite). Figure 2(a) shows the case where water is pressurized and injected into the borehole 3 of the core sample 2, with the pressurized state and the state of AE energy released below, while Figure 2(b) shows the case where supercritical CO2 is pressurized and injected into the borehole 3 of the core sample 2, with the pressurized state and the state of AE energy released below. Note that the CO2 shown in the graph in Figure 2(b) correctly means supercritical CO2.

[0020] As is clear from Figure 2(a), when pressurized water is injected, a large amount of AE energy is released instantaneously at a certain point (after 250 seconds, at approximately 70 MPa), causing Core Sample 2 to crack. In contrast, when pressurized supercritical CO2 is injected as shown in Figure 2(b), small amounts of AE energy are gradually and intermittently released after 250 seconds, starting from around 40 MPa, which tends to cause fine cracks to form. Furthermore, the fracturing initiation pressure was lower with supercritical CO2, dropping from approximately 70 MPa (water) to approximately 40 MPa (CO2). These results suggest that fracturing with supercritical CO2 requires less fracturing energy than fracturing with water, gradually generating finer cracks, and also reduces the risk of induced earthquakes. [Example]

[0021] Next, to reduce the amount of supercritical CO2 used, we also conducted an experiment using the apparatus 1 shown in Figure 1. This experiment first injected supercritical CO2 under pressure, followed by a boost of the injected supercritical CO2 with pressurized water. The experimental conditions and procedures were the same as those described above. Specifically, a dry rock core sample 2 was placed in a pressure vessel 10. The temperature, confining pressure, and axial stress were then set to predetermined values, and AE measurements were initiated. First, 10 MPa and 250°C supercritical CO2 was injected into the borehole 3 via a pump 13 for approximately 20 minutes. Subsequently, while the supercritical CO2 remained in the piping, pressurized water at 250°C was injected at a constant flow rate (1 mL / min) instead of the supercritical CO2. This experiment verified the crack formation caused by a two-stage injection method: first injecting supercritical CO2 and then injecting pressurized water.

[0022] As is clear from Figure 3(a), during the initial supercritical CO2 injection phase (up to approximately 250 seconds), cracks began to appear gradually around 100 seconds into the core. Then, at around 250 seconds, water reached the core sample, supercritical CO2 injection stopped, and the injection phase switched to water injection. However, the AE energy released was not significantly different from that in the case of CO2-only fracturing, indicating that the boosting water had almost no effect on the AE energy. In other words, even when supercritical CO2 was injected first and then boosted with water, the AE energy generated by the boosting water was similar to that in the case of CO2 alone, and sufficient cracks were successfully generated, demonstrating that the boosting effect of water also had a certain effect. This is also evident from the X-ray CT image of core sample 2 in Figure 3(b). If we conceptualize the crack mechanism shown in Figure 3(b), we can show it diagrammatically as shown in Figure 4. Figure 4 is a schematic diagram conceptualizing the crack mechanism. [Example]

[0023] Based on the experimental results described above, we considered the practical application of the rock fracturing method in actual well drilling. FIG. 5 is a conceptual diagram of practical application of a method for fracturing rock mass in a borehole using supercritical CO2 and subsequent boosting water according to a third embodiment of the present invention.

[0024] In Figure 5, reference numeral 31 denotes the artificial reservoir, 32 denotes the open well section, 33 denotes a straddle packer, 34 denotes the annular well section, 35 denotes the well casing, 36 denotes the transfer pipe, and 37 denotes the fracturing pump. The casing section 35 in Figure 5 is protected by the straddle packer 33 to prevent the annulus section 34 from being subjected to pressures greater than the casing's withstand pressure. A diaphragm pump is used to inject supercritical CO2, but the range of pressure that can be achieved with a high-flow pump is limited by the High-Pressure Gas Safety Act. Therefore, a low-flow, high-pressure pump is used to inject the CO2. Once a certain amount of opening has been achieved, a high-flow, low-pressure pump is used to expand the crack.

[0025] Then, by switching to water injection to further widen the crack, it is possible to reduce the amount of supercritical CO2 required. This is because procuring supercritical CO2 in large quantities takes time and costs more than procuring water, so the two-stage method is practical and particularly promising, as it is expected to reduce costs and procurement time.

[0026] To maintain the cracks when they occur, proppants used in oil and natural gas production (proppants are support materials embedded inside cracks formed in the strata during fracturing, a type of extraction technology for oil, natural gas, and geothermal energy, to prevent them from closing. Proppants are generally made from sand or ceramics and processed into granules, which are mixed into the fluid that fills the well) are not used due to their poor heat resistance. This is because it is better not to use proppants in high-temperature geothermal areas, so the "shear stress" of pressurized supercritical CO2 or water is used to maintain open cracks. That is, a pressure pipe 36 is inserted into the mine 32, and is closed with a straddle packer 33 installed at the bottom of the casing 35, filling the inside with supercritical CO2. After that, the pipe is filled with water while the supercritical CO2 is still present, and when pressure is applied, cracks occur in the open hole 32, and the cracks that occur are maintained by the shear stress of the supercritical CO2 or water that is constantly pressurized.

[0027] The fracturing pump 37 used in the implementation of the rock fracturing method for well drilling according to the third embodiment has a maximum pressure of 20 MPa and a maximum flow rate of 14.58 m3, although the injection conditions for supercritical CO2 and pressurized water, the switching time to supercritical CO2 and pressurized water, etc. vary depending on the underground structure being implemented. 3 Three large-flow fracturing pumps with a maximum flow rate of 45 MGa and 74 L / h (e.g., Nikkiso metering pump LDG: model G3R) are used in series, and any pressure shortfall is made up with a smaller-scale fracturing pump that can inject at a higher pressure (e.g., Nikkiso metering pump model G3R). As a result, it becomes possible to inject supercritical CO2 and water alternately at a maximum pressure of 45 MGa and a maximum flow rate of 74 L / h. The maximum flow rate of 74 L / h is determined by the pump specifications.

[0028] Experimental results using the above-mentioned device and a core sample (Komatsu andesite)2 showed that branched fine cracks can be formed at lower pressures than when rock is fractured using only water, because the AE (Acoustic Emission) energy released is small and intermittent.

[0029] Furthermore, even if supercritical CO2 is injected first and then water is injected afterwards while the supercritical CO2 is left in place, the formation of cracks is similar to that in the case of only supercritical CO2 injection, and the AE energy release is significantly smaller than that of water alone. As for the mechanism, as shown in Figure 4, by first generating a crack with supercritical CO2 and then pushing it with water, the opening can be widened while pressurizing the supercritical CO2 that has already been injected. By using supercritical CO2 to fracture rock, the energy required to generate AE is reduced, allowing for a corresponding reduction in the amount of pressure applied, thereby reducing the risk of induced earthquakes compared to fractures using water alone. [Example]

[0030] In the rock crushing method of this embodiment, tests and measurements were carried out in the following manner to confirm the effect of improving the permeability when a chelating agent or the like is contained. (1) A 25 mm diameter and 25 mm long piece of Emochi andesite (andesitic tuff) cut with a rock cutter was prepared as an experimental sample. (2) The cracks created by cutting with this rock cutter simulate cracks formed by crushing. (3) The experimental sample was placed in a pressure vessel equipped with a mantle heater, and the initial permeability was measured using pure water at a temperature of 150°C under effective confining pressure conditions of approximately 5 to 30 MPa (back pressure was fixed at 5 MPa, and the confining pressure was varied) (Fig. 7). (4) Then, under the condition of an effective confining pressure of approximately 5 MPa, water containing 0.25 wt% scleroglucan, 20 wt% GLDA-Na4, and 0.2% NH4HF2 at pH 2 was passed through the tube at 0.25 mL / min for 4 hours. (5) After that, pure water was passed through to wash away the chelating agent-containing water, and the permeability was measured in the same manner as in 3 above (Figure 7). Figure 7A shows that the flow of chelating agent-containing water was started from this state (simulating a state in which the effective confining pressure is decreasing during fracturing). Figure 7B shows that if chelating agent-containing water is not passed through, the effective confining pressure after fracturing will remain high, and this low permeability will be achieved, for example. Figure 7C shows that when chelating agent-containing water is passed through, the effective confining pressure after fracturing will remain high and the permeability will increase. (6) Furthermore, after the experimental sample was removed from the pressure vessel, pore analysis based on X-ray CT data confirmed the formation of pores due to mineral dissolution in the chelating agent-containing water (Fig. 8). [Industrial Applicability]

[0031] The present invention is used for rock fracturing and reservoir creation using supercritical CO2, and has industrial applicability. [Explanation of symbols]

[0032] 1 Pressure equipment 2 Core Sample 3. Borehole 4 manual pumps 5 Hydraulic jack 6 Load cell 7. Displacement gauge 8 pistons 9a, 9b Copper gasket 10 Triaxial cell (pressure vessel) 11 Electric furnace 12 AE energy sensor 13 Syringe pump 14 Pressure gauge 15 Thermocouple 16 Syringe Pump 17 Pressure gauge 18 Piston 19 Polyethylene resin 20, 21 Thermocouples 31 Geothermal reservoir 32 Bare pit 33 Straddle Packer 34 Well annular section 35 Well casing 36 Transfer pipe 37 Crushing pump (diaphragm pump)

Claims

1. supercritical CO ２ A method for fracturing rock mass near a wellbore using The supercritical CO ２ CO is injected into the well ２ A press-fitting step; The supercritical CO ２ After the injection of the supercritical CO2 is stopped, pressurized water is injected into the well. ２ a pressurized water injection step of pushing the above with pressurized water; A rock crushing method comprising the steps of:

2. The rock fracturing method according to claim 1 , wherein the pressurized water contains a chelating agent.

3. The rock breaking method according to claim 2, wherein the chelating agent is a biodegradable chelating agent.

4. 3. The rock breaking method according to claim 2, wherein the chelating agent is 4Na glutamic acid diacetate.

5. The rock fracturing method according to claim 2, wherein the pressurized water is acidic.

6. The rock fracturing method according to claim 2, wherein the pressurized water further contains hydrogen fluoride.

7. The rock breaking method according to claim 2, wherein the pressurized water further contains a thickener.

8. The CO ２ the injecting step comprises injecting supercritical CO at a first pressure ２ a first CO ２ Injection step; ２ a step performed after the step of injecting supercritical CO at a second pressure lower than the first pressure; ２ a second CO ２ 8. The rock breaking method according to claim 1, further comprising a press-in step.

9. A rock breaking method according to any one of claims 1 to 7, characterized in that after the step of pushing with pressurized water, a pressurized water removal step is included in which water is flowed into the inside of the crack to wash away the pressurized water, and / or the pressurized water is flowed back from the crack to recover it.

10. A reservoir creation method, comprising creating a reservoir near the borehole by using the rock fracturing method according to any one of claims 1 to 7.

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