CN115853488A - Multistage fracturing method for reducing cracking pressure of dry hot rock reservoir by using supercritical water - Google Patents
Multistage fracturing method for reducing cracking pressure of dry hot rock reservoir by using supercritical water Download PDFInfo
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Abstract
The invention belongs to the technical field of development of geothermal resources of hot dry rocks, and particularly relates to a multi-stage fracturing method for reducing the fracturing pressure of a hot dry rock reservoir by using supercritical water. The invention aims to provide a multistage fracturing method for reducing the fracturing pressure of a dry hot rock reservoir by using supercritical water, and solves the problem that a large-volume dry hot rock fracture network reservoir is difficult to build. According to the fracturing method, supercritical water is used as fracturing fluid to perform hot dry rock reservoir multistage fracturing, and the supercritical water has the characteristics of low viscosity and high fluidity, so that the supercritical water can quickly permeate into gaps of low-porosity and low-permeability hot dry rock reservoirs to reduce the effective stress of a stratum in the fracturing process, further the fracture pressure of hot dry rock reservoir fracturing construction is reduced, the fracturing construction efficiency is improved, and a complex hot dry rock fracture network is formed.
Description
Technical Field
The invention belongs to the technical field of hot dry rock geothermal resource development, and particularly relates to a multistage fracturing method for reducing the fracturing pressure of a hot dry rock reservoir by using supercritical water.
Background
The Hot Dry Rock (HDR) geothermal resource reserves are huge, and the development potential is very large. According to statistics, the amount of hot dry rock resources available for human exploitation on the earth is 30 times of the amount of all oil, natural gas and coal resources on the earth. The main method for developing geothermal resources of dry and hot rocks is an Enhanced Geothermal System (EGS), i.e. by means of hydraulic fracturing, seepage channels of complex fracture networks are formed in high-temperature dry and hot rock masses, low-hole and low-seepage high-temperature rock masses in underground deep parts are built into artificial geothermal reservoirs with higher permeability and more heat exchange areas, and considerable heat energy is economically extracted from the artificial geothermal reservoirs for long term use.
The hydraulic fracturing technology destroys the original ground stress field of a high-temperature rock body through the injection of high-pressure fluid, thereby activating the existing fractures and generating new fractures, increasing the flow guide and heat exchange capacity of the rock body, and improving the connectivity of an injection well and a production well. Although the hydraulic fracturing technology is mature and applied to the field of oil and gas, the fracture pressure of the dry hot rock reservoir is far higher than that of a common oil and gas reservoir due to the characteristics of hard texture (high mechanical strength), high temperature, high stress and the like, and the difficulty and uncertainty of the dry hot rock reservoir transformation are increased. In addition, the high-pressure hydraulic fracturing operation process accompanied by the high fracture pressure of the hot dry rock reservoir has the risk of inducing earthquake, and the scale and industrialization of hot dry rock geothermal development are seriously restricted. For example, the Bassel (Base l) hot dry rock development project in Switzerland causes more than four 3-level earthquakes during water injection, causes building damage, forces the project to terminate, causes huge investment failure, and causes a great deal of legal disputes. The dry hot rock development project of Korea project (Pohang) in 2017 triggered M on nearby faults W 5.4 earthquake and causing serious economic loss, the korean government is forced to stop the operation of the project.
It can be seen that inducing earthquakes is an important determinant factor for the smooth implementation of hot dry rock mining, particularly for EGS projects employing hydraulic fracturing techniques. The general attention of academia and industry has been brought about by exploring a 'soft fracturing' technology aiming at effectively reducing the fracturing pressure of a dry-hot rock reservoir. At present, the main technical idea is to use the thermal stress effect caused by the temperature difference between the injected low-temperature fluid and the underground high-temperature rock mass to assist the dry hot rock fracturing construction.
Chinese patent CN115126460A discloses a fracturing method for reducing the fracture pressure of hot dry rock formation. According to the method, cold water is continuously injected into a fracturing oil pipe to continuously cool the rock of the borehole wall at the open hole section, micro cracks are formed on the borehole wall until the temperature of the stratum is reduced to a preset temperature, the cold water injection is stopped, the temperature of the stratum is recovered, the circulation is repeated, the rock of the borehole wall is subjected to circulating low-temperature impact to cause the damage of the borehole wall, and further the fracture pressure of dry and hot rock stratum fracturing construction is reduced. Chinese patent CN111173485A discloses a method for increasing hot dry rock thermal storage transformation volume. According to the method, ice water is injected into hot dry rock to generate a large number of micro cracks, the micro cracks are expanded under the critical discharge capacity and pressure, the pump is stopped, the well is stewed to recover the temperature, then the ice water is injected, the micro cracks are expanded, and a large-range micro crack system without main cracks is formed in the hot dry rock stratum after multiple cycles. Chinese patent CN108979609A discloses a method for assisting hydraulic fracturing and seam making by alternately spraying high-temperature and low-temperature fluids on deep dry hot rock. The method alternately injects high-temperature high-pressure fluid and low-temperature water into the main cracks in a short alternating time, the rock on the surfaces of the main cracks generates micro cracks through the thermal action of great temperature difference and the impact action generated by jet flow, the micro cracks are further expanded under the action of low-temperature water-based fracturing fluid and high pressure through multi-stage fracturing to form more micro cracks, and the micro cracks are repeatedly circulated until the main cracks and the micro cracks are mutually lapped and communicated to form crack groups and/or crack zones. Chinese patent CN108661617A discloses a fracturing method for increasing the complexity of artificial net-sewing of high-temperature stratum. The method comprises the steps of injecting low-temperature working fluid into a high-temperature stratum, generating strong cold and hot stress impact action by utilizing high temperature difference between the high-temperature working fluid and the high-temperature working fluid, inducing rock around a well to generate micro cracks, then injecting fracturing fluid to enable the micro cracks to continue to expand forwards, and finally injecting temporary blocking diverting fluid to bridge and block artificial cracks to force the cracks to divert to form multi-branch cracks. Chinese patent CN110173246A discloses a method for improving heat recovery rate by water-liquid nitrogen alternate fatigue fracturing of dry hot rock. The method comprises the steps of fracturing a hot dry rock reservoir by adopting high-pressure water jet to form a main fracture, then performing liquid nitrogen jet at ultralow temperature, generating a great temperature difference of nearly 400 ℃ in the hot dry rock containing water in the liquid nitrogen gasification process to enable the hot dry rock to generate a micro-fracture inside the hot dry rock, and simultaneously enabling the gasified volume-expanded nitrogen to enter the micro-fracture for re-fracturing; and repeating the steps, and continuously performing alternate fatigue fracturing by using water and liquid nitrogen respectively so as to form a complex communicated fracture network in the hot dry rock stratum. Chinese patent CN110145290A discloses a dry hot rock geothermal well liquid nitrogen multistage fracturing system and method. The method establishes the connection between the liquid nitrogen system and the continuous oil pipe, and performs liquid nitrogen step-by-step fracturing by expelling air and moisture in the system and filling liquid nitrogen to sequentially complete fracturing operation of each layer section, thereby effectively reducing fracture initiation pressure of the reservoir fracture of the hot dry rock and saving water consumption. Chinese patent CN105696996A discloses a construction method of hot dry rock geothermal artificial heat storage. According to the method, supercritical carbon dioxide fracturing is carried out along a weak surface or an interlayer formed by igneous rock phases to generate a main crack, then large-displacement hydraulic fracturing is carried out in the main crack to generate secondary fracture, and the dry-hot rock body is subjected to volume fracture or cluster fracture under cyclic fracturing to construct the dry-hot rock artificial heat storage.
In summary, for the improvement construction of the fracturing of the hot dry rock reservoir, induced micro-fractures are mainly forced to be generated around a well or near a main fracture through the temperature effect in the fracturing process of the hot dry rock reservoir at present, and the induced micro-fractures are further extended to form branch fractures, so that the complexity of the fractures is improved, and the heat exchange area is increased. However, the formation of the hot dry rock is limited by the slow heat conduction process of the hot dry rock, and the thermal stress effect generated by injecting the cryogenic fluid in the prior art is mainly concentrated around the wellbore, but the effect on the hot dry rock reservoir in the far well field area cannot be generated, so that the fracture pressure of the hot dry rock reservoir cannot be effectively reduced, and the formation of the large-volume hot dry rock reservoir is difficult. In addition, the existing fracturing method causes the main tensile damage of the hot dry rock mass, usually forms a single high-permeability crack, has small heat storage and heat exchange area and is not suitable for the high-efficiency exploitation of the hot dry rock geothermy. Therefore, there is a need for further exploration of reservoir construction methods that can effectively reduce the fracturing pressure of the hot dry rock reservoir and form a large-volume hot dry rock fracture network.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a multistage fracturing method for reducing the fracturing pressure of a hot dry rock reservoir by using supercritical water, and solves the problem that a large-volume hot dry rock fracture network reservoir is difficult to build. According to the fracturing method, supercritical water is used as fracturing fluid to perform hot dry rock reservoir multistage fracturing, and the supercritical water has the characteristics of low viscosity and high fluidity, so that the supercritical water can quickly permeate into gaps of low-porosity and low-permeability hot dry rock reservoirs to reduce the effective stress of a stratum in the fracturing process, further the fracture pressure of hot dry rock reservoir fracturing construction is reduced, the fracturing construction efficiency is improved, and a complex hot dry rock fracture network is formed.
The technical scheme of the invention is as follows:
the invention provides a multistage fracturing method for reducing cracking pressure of a dry hot rock reservoir by using supercritical water, which comprises the following steps:
selecting a target area for dry hot rock development, and arranging a well pattern of a production well and an injection well in the target area for dry hot rock development;
drilling a well to a target dry hot rock reservoir in the dry hot rock development target area, and performing open hole well completion on the target dry hot rock reservoir;
thirdly, putting a fracturing oil pipe into the dry-hot rock well to a preset depth, wherein an underground heating device, a packer and temperature and pressure sensors are arranged at the bottom of the fracturing oil pipe;
injecting a plurality of volumes of fracturing pad fluid (clear water) into the target fracturing interval before supercritical water fracturing so as to effectively wet the dry hot rock stratum around the target fracturing interval and improve the subsequent supercritical water fracturing effect;
fifthly, setting the packer, and continuously injecting preheated clean water to the bottom of the fracturing oil pipe;
step six, opening an underground heating device at the bottom of the fracturing oil pipe to heat the injected clean water, expanding the clean water after being heated, simultaneously increasing the pressure and the temperature, monitoring the state of the clean water in real time by utilizing the temperature and pressure sensors, and judging whether the clean water becomes supercritical water or not;
step seven, carrying out hydraulic stimulation on the target interval hot dry rock reservoir by using the supercritical water formed in the step six through heating to form a fracture network;
pumping the uniformly mixed sand-carrying fluid and the propping agent into the formed fracture network, and then pumping the displacement fluid to uniformly distribute the propping agent into the formed fracture network to form a stable dry-hot rock fracture network reservoir;
step nine, plugging the formed hot dry rock fracture network reservoir by using the packer as required, repeating the step four to the step eight, and performing hydraulic stimulation on the hot dry rock reservoir of other target intervals by using supercritical water to complete supercritical water multistage staged fracturing;
step ten, after fracturing of the dry hot rock reservoirs of all preset intervals, closing the well, and completing construction of the large-volume dry hot rock fracture network reservoir;
further, in the third step, the downhole heating device may be an electric heating device, or may be a fuel combustion heating device, and the fuel may be liquid hydrogen, liquid methane, or the like; further, in the fourth step, the fracturing pad fluid with the plurality of volumes is determined according to parameters such as the thickness of the target fracturing interval, the porosity and the like;
further, in step five, the preheated clean water can be heated at the surface in any form, including but not limited to electric heating, solar heating, combustion heating, etc.;
further, in the sixth step, the supercritical water means that the temperature and the pressure of water reach 374 ℃ and 22.1MPa respectively;
furthermore, in the seventh step, the supercritical water has a lower viscosity, for example, the viscosity of water at normal temperature and normal pressure is 1.0mPa · s, and the viscosity of water at 450 ℃ and 40mPa is 0.039mPa · s, and the low viscosity can significantly enhance the seepage capability of the supercritical water in the hot dry rock stratum, reduce the fracture pressure of the hot dry rock stratum, and increase the transformation range of the hot dry rock reservoir;
further, in the ninth step, the supercritical water multistage staged fracturing, wherein the fracturing interval can be one-stage fracturing or multistage fracturing;
furthermore, in the ninth step, the supercritical water multistage staged fracturing, whether vertical wells, inclined wells or horizontal wells, preferably takes the multistage staged fracturing from the bottom of the shaft to the top in sequence.
The invention has the beneficial effects that: (1) Compared with low-temperature hydraulic fracturing, supercritical hydraulic fracturing can reduce the cracking pressure of a hot dry rock reservoir. The high injection pressures inevitable with low temperature water fracturing construction may cause earthquakes, posing a threat to the safety of construction personnel and surface facilities. In the supercritical water fracturing process, water with low viscosity and high fluidity can quickly permeate into gaps of a low-pore and low-permeability dry hot rock reservoir, namely, in an area far away from an injection well, the pore pressure of the dry hot rock is increased, the effective stress on a rock framework is reduced, and natural fractures are easily induced to generate shear failure and new fractures, so that the cracking pressure of the dry hot rock reservoir can be effectively reduced, and the earthquake risk caused by the fracturing construction of the dry hot rock reservoir is reduced.
(2) Supercritical water fracturing can produce a complex network of hot and dry rock fractures compared to low temperature water fracturing. The low-temperature water fracturing process mainly causes the dry hot rock reservoir to generate tensile damage to form cracks, and the stress concentration at the tip of the tensile damage provides stronger inertia in a certain direction and controls the expansion of the cracks, so that single high-permeability cracks are usually formed, the heat exchange area is small, and the low-temperature water fracturing process is not suitable for the high-efficiency exploitation of the geothermal energy of the dry hot rock. In the supercritical water fracturing process, a high-temperature low-viscosity fluid enters a dry hot rock reservoir to cause more crack development forms, including a tensile crack and a shearing crack, and the initiation directions of the cracks caused by the shearing stress and the tensile stress are not parallel, so that expanded natural cracks and newly-grown cracks are more easily communicated to form a complex dry hot rock crack network, and the complex crack network reservoir has important significance for the efficient development of dry hot rock geothermy.
The technical advantages of the two points of dry heat rock reservoir fracturing by using supercritical water are proved by indoor experimental research.
Drawings
Fig. 1 shows a schematic construction diagram of a single-stage fracturing method for reducing fracturing pressure of a dry hot rock reservoir by using supercritical water according to the invention.
Figure 2 shows the contour plot of the viscosity of water under different temperature and pressure conditions.
Fig. 3 shows a schematic of a multi-stage fracturing method using supercritical water to reduce the fracturing pressure of a hot dry rock reservoir according to the present invention.
In the figure, 1 is a wellhead device, 2 is a casing well completion, 3 is an annulus, 4 is a fracturing oil pipe, 5 is an open hole well completion, 6 is a target hot dry rock reservoir, 7 is a booster injection pump, 8 is a preheating device, 9 is an injection pipe, 10 is a liquid return pipe, 11 is a water storage tank liquid level, 12 is a water storage tank, 13 is a filter screen, 14 is a packer, 15 downhole heating devices, 16 is a temperature and pressure sensor, 17 is a hot dry rock fracture network, 18 is a first-stage hot dry rock fracture network, 19 is a second-stage hot dry rock fracture network, and 20 is a third-stage hot dry rock fracture network.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.
Example 1, supercritical water single stage fracturing:
determining a target dry hot rock development target area according to the previous exploration data, and carrying out well pattern arrangement of a production well and an injection well in the target dry hot rock development area.
And carrying out dry hot rock reservoir drilling and completion construction in the dry hot rock development target area. Specifically, as shown in fig. 1, a well is drilled to a target dry hot rock reservoir 6 in a dry hot rock development target area, the target dry hot rock reservoir 6 is subjected to open hole well completion 5, and a casing well completion 2 is arranged above the target dry hot rock reservoir 6. And connecting the fracturing oil pipe 4, and lowering the fracturing oil pipe 4 into the dry hot rock well to a preset depth. The bottom of the fracturing oil pipe 4 is connected with a packer 14, a downhole heating device 15 and a temperature and pressure sensor 16. The packer 14 is located above the temperature and pressure sensors 16. The downhole heating means 15 may be an electrical heating means or a fuel fired heating means, the fuel being liquid hydrogen, liquid methane, etc. According to the invention, the wellhead device 1 is installed before the fracturing oil pipe 4 is lowered to ensure the safety of the wellhead; packer 14 remains unset during the running of frac tubing 4.
And after the fracturing oil pipe 4 is completely put in, the fracturing oil pipe is connected with a ground manifold. The ground manifold comprises a liquid injection pipe 9 and a liquid return pipe 10. The liquid injection pipe 9 is respectively connected with the preheating device 8 and the booster injection pump 7. Annotate the one end of liquid pipe 9 and be connected with fracturing oil pipe 4, the other end is connected with subaerial tank 12, and annotates the one end that is in tank 12 of liquid pipe 9 and extend to the bottom of tank 12 for leading-in to fracturing oil pipe 4 with the fracturing fluid in the tank 12. One end of the return pipe 10 is communicated with an annulus 3 formed between the fracturing oil pipe 4 and the casing completion 2, the other end of the return pipe is connected with the water storage tank 12, and the return pipe 10 is connected to the upper end of the water storage tank 12 and used for returning return liquid in the annulus 3 to the water storage tank 12. In order to prevent the liquid injection pipe 9 from being blocked, a filter screen 13 which is vertically distributed is arranged inside the water storage tank 12, and the liquid injection pipe 9 and the liquid return pipe 10 which are positioned in the water storage tank 12 are respectively positioned at two sides of the filter screen 13. Impurities such as rock debris can be effectively filtered, and therefore the rock debris in the return liquid is prevented from blocking the liquid injection pipe 9. The pre-heating device 8 may perform heating in any form, including but not limited to electrical heating, solar heating, combustion heating, and the like.
After completion of the wellhead 1 and surface manifold connections, the packer 14 is left set. And continuously injecting fracturing pad fluid (clear water) into the fracturing oil pipe 4, and observing whether the pressure is continuously increased through the temperature and pressure sensor 16 to judge whether the packer 14 works normally. The injection volume of the fracturing pad fluid needs to be determined according to parameters such as the thickness, the porosity and the like of a target fracturing layer section, for example, for granite strata, the injection volume of the fracturing pad fluid can be 10-100 m 3 。
And after the fracturing prepad fluid is injected, stopping pumping and stewing for several hours so as to effectively wet the target dry hot rock reservoir 6 at the periphery of the fracturing layer section. Keeping packer 14 setting, opening preheating device 8, opening downhole heating device 15, continuously injecting the clear water after preheating into fracturing oil pipe 4 through booster injection pump 7. The clear water that gets into fracturing oil pipe 4 bottom receives heating device 15's continuous heating, makes clear water temperature and pressure of packer 14 lower part continuously rise, utilizes temperature and pressure sensor 16 real-time supervision clear water state, judges whether it becomes supercritical water, and the temperature and the pressure of supercritical water need reach 374 ℃ and 22.1MPa respectively. The supercritical water has a lower viscosity as shown in fig. 2. The low viscosity characteristic can obviously enhance the seepage capability of supercritical water in the hot dry rock stratum, reduce the fracture pressure of the hot dry rock stratum and enlarge the transformation range of the hot dry rock reservoir.
And (3) carrying out hydraulic stimulation on the target hot dry rock reservoir 6 by using supercritical water formed after the heating of the underground heating device 15, after the supercritical water fracturing is completed, pumping the uniformly mixed sand-carrying liquid and the propping agent into the formed fracture network, and then pumping the displacement liquid into the formed fracture network so that the propping agent is uniformly distributed in the formed fracture network to form a hot dry rock fracture network 17.
And closing the well and finishing the construction of the reservoir of the hot dry rock fracture network 17.
Example 2, supercritical water multistage fracturing:
determining a target dry hot rock development target area according to the previous exploration data, and carrying out well pattern arrangement of a production well and an injection well in the target dry hot rock development area.
And carrying out dry hot rock reservoir drilling and completion construction in the dry hot rock development target area. Specifically, as shown in fig. 3, a well is drilled to a target dry hot rock reservoir 6 in a dry hot rock development target area, the target dry hot rock reservoir 6 is subjected to open hole well completion 5, and a casing well completion 2 is arranged above the target dry hot rock reservoir 6. And connecting the fracturing oil pipe 4, and lowering the fracturing oil pipe 4 into the dry hot rock well to a preset depth. The bottom of the fracturing oil pipe 4 is connected with a packer 14, a downhole heating device 15 and a temperature and pressure sensor 16. The packer 14 is located above the temperature and pressure sensors 16. The downhole heating means 15 may be an electrical heating means or a fuel fired heating means, the fuel being liquid hydrogen, liquid methane, etc. According to the invention, the wellhead device 1 is installed before the fracturing oil pipe 4 is lowered to ensure the safety of the wellhead; packer 14 remains unset during the run of frac tubing 4.
And after the fracturing oil pipe 4 is completely put in, the fracturing oil pipe is connected with a ground manifold. The ground manifold comprises a liquid injection pipe 9 and a liquid return pipe 10. The liquid injection pipe 9 is respectively connected with the preheating device 8 and the booster injection pump 7. Annotate the one end of liquid pipe 9 and be connected with fracturing oil pipe 4, the other end is connected with subaerial tank 12, and annotates the one end that is in tank 12 of liquid pipe 9 and extend to the bottom of tank 12 for leading-in to fracturing oil pipe 4 with the fracturing fluid in the tank 12. One end of the return pipe 10 is communicated with an annulus 3 formed between the fracturing oil pipe 4 and the casing completion 2, the other end of the return pipe is connected with the water storage tank 12, and the return pipe 10 is connected to the upper end of the water storage tank 12 and used for returning return liquid in the annulus 3 to the water storage tank 12. In order to prevent the liquid injection pipe 9 from being blocked, a filter screen 13 which is vertically distributed is arranged inside the water storage tank 12, and the liquid injection pipe 9 and the liquid return pipe 10 which are positioned in the water storage tank 12 are respectively positioned at two sides of the filter screen 13. Impurities such as rock debris can be effectively filtered, and therefore the rock debris in the return liquid is prevented from blocking the liquid injection pipe 9. The pre-heating device 8 may perform heating in any form, including but not limited to electrical heating, solar heating, combustion heating, and the like.
After the wellhead 1 and surface manifold connections are completed, the packers 14 are left set. And continuously injecting fracturing pad fluid (clear water) into the fracturing oil pipe 4, and observing whether the pressure is continuously increased through the temperature and pressure sensor 16 to judge whether the packer 14 works normally. The injection volume of the fracturing pad fluid needs to be determined according to parameters such as the thickness, the porosity and the like of a target fracturing layer section, for example, for granite strata, the injection volume of the fracturing pad fluid can be 10-100 m 3 。
And after the fracturing prepad fluid is injected, stopping pumping and stewing for several hours so as to effectively wet the target dry hot rock reservoir 6 at the periphery of the fracturing layer section. Keeping packer 14 setting, opening preheating device 8, opening downhole heating device 15, continuously injecting the clear water after preheating into fracturing oil pipe 4 through booster injection pump 7. The clear water that gets into fracturing oil pipe 4 bottom receives heating device 15's continuous heating, makes clear water temperature and pressure of packer 14 lower part continuously rise, utilizes temperature and pressure sensor 16 real-time supervision clear water state, judges whether it becomes supercritical water, and the temperature and the pressure of supercritical water need reach 374 ℃ and 22.1MPa respectively. The supercritical water has a lower viscosity as shown in fig. 2. The low viscosity characteristic can obviously enhance the seepage capability of supercritical water in the hot dry rock stratum, reduce the fracture pressure of the hot dry rock stratum and enlarge the transformation range of the hot dry rock reservoir.
And (3) carrying out hydraulic stimulation on the target hot dry rock reservoir 6 by using supercritical water formed after the heating of the underground heating device 15, after the supercritical water fracturing is completed, pumping the uniformly mixed sand-carrying liquid and the propping agent into the formed fracture network, and then pumping the displacement liquid into the formed fracture network so that the propping agent is uniformly distributed in the formed fracture network to form a first-stage hot dry rock fracture network 18.
After the first-stage hot dry rock fracture network 18 reservoir construction is completed, lifting the fracturing oil pipe 4 to the depth of a second-stage hot dry rock fracture layer, plugging the formed first-stage hot dry rock fracture network 18 by using a packer, and repeating the first-stage hot dry rock fracture network 18 reservoir construction process to form second-stage hot dry rock fracture network 19 reservoir construction; and after the second-stage hot dry rock fracture network 19 reservoir construction is completed, lifting the fracturing oil pipe 4 to the depth of the third-stage hot dry rock fracture layer, plugging the formed first-stage hot dry rock fracture network 18 and the second-stage hot dry rock fracture network 19 by using a packer, and repeating the second-stage hot dry rock fracture network 19 reservoir construction process to form the third-stage hot dry rock fracture network 20 reservoir construction. The embodiment provides a three-stage staged fracturing operation process of supercritical water, and other supercritical water staged fracturing of any stages can be set according to actual needs. In addition, the supercritical water multistage staged fracturing can be a vertical well, an inclined well and a horizontal well, but the supercritical water multistage staged fracturing should be sequentially performed from the bottom of a well shaft to the top in a priority manner.
And (4) closing the well after fracturing of the dry hot rock reservoir of all preset stages is completed, and completing construction of the large-volume dry hot rock fracture network reservoir.
Claims (8)
1. A multistage fracturing method for reducing the fracturing pressure of a dry hot rock reservoir by using supercritical water is characterized by comprising the following steps:
selecting a target area for dry hot rock development, and arranging a well pattern of a production well and an injection well in the target area for dry hot rock development;
drilling a well to a target dry hot rock reservoir in the dry hot rock development target area, and performing open hole well completion on the target dry hot rock reservoir;
thirdly, putting a fracturing oil pipe into the dry-hot rock well to a preset depth, wherein an underground heating device, a packer and temperature and pressure sensors are arranged at the bottom of the fracturing oil pipe;
injecting a plurality of volumes of fracturing prepad liquid into the target fracturing layer section before supercritical water fracturing so as to effectively wet the hot rock formation around the well of the target fracturing layer section and improve the subsequent supercritical water fracturing effect;
fifthly, setting the packer, and continuously injecting preheated clean water to the bottom of the fracturing oil pipe;
step six, opening an underground heating device at the bottom of the fracturing oil pipe to heat the injected clean water, expanding the clean water after being heated, simultaneously raising the pressure and the temperature, monitoring the state of the clean water in real time by utilizing the temperature and pressure sensors, and judging whether the clean water becomes supercritical water or not;
step seven, carrying out hydraulic stimulation on the target interval hot dry rock reservoir by using the supercritical water formed in the step six through heating to form a fracture network;
pumping the uniformly mixed sand-carrying fluid and the propping agent into the formed fracture network, and then pumping the displacement fluid to uniformly distribute the propping agent into the formed fracture network to form a stable dry-hot rock fracture network reservoir;
step nine, plugging the formed hot dry rock fracture network reservoir by using the packer as required, repeating the step four to the step eight, and performing hydraulic stimulation on the hot dry rock reservoir of other target intervals by using supercritical water to complete supercritical water multistage staged fracturing;
and step ten, after fracturing all the dry hot rock reservoirs in the preset intervals, closing the well, and completing construction of the large-volume dry hot rock fracture network reservoir.
2. The multi-stage fracturing method for reducing the fracturing pressure of a hot dry rock reservoir by using supercritical water as claimed in claim 1, wherein in the third step, the downhole heating device can be an electric heating device or a fuel combustion heating device, and the fuel can be liquid hydrogen, liquid methane and the like.
3. The multistage fracturing method for reducing the fracturing pressure of the dry hot rock reservoir by using the supercritical water as claimed in claim 1, wherein in step four, the fracturing pad fluid with a plurality of volumes is determined according to parameters such as the thickness and the porosity of a target fracturing interval.
4. The multi-stage fracturing method of claim 1, wherein in step five, the preheated clean water can be heated at the surface in any form, including but not limited to electric heating, solar heating, combustion heating, etc.
5. The multi-stage fracturing method for reducing the fracturing pressure of a hot dry rock reservoir by using supercritical water as claimed in claim 1, wherein in step six, the supercritical water means that the temperature and the pressure of water reach 374 ℃ and 22.1MPa respectively.
6. The multi-stage fracturing method for reducing the fracturing pressure of the dry hot rock reservoir by using the supercritical water as claimed in claim 1, wherein in step seven, the supercritical water has lower viscosity, such as the viscosity of water at normal temperature and normal pressure is 1.0 mPa-s, the viscosity of water at 450 ℃ and 40mPa is 0.039 mPa-s, and the low viscosity can significantly enhance the seepage capability of the supercritical water in the dry hot rock reservoir, reduce the fracturing pressure of the dry hot rock reservoir and increase the transformation range of the dry hot rock reservoir.
7. The multi-stage fracturing method for reducing fracturing pressure of the dry hot rock reservoir by using supercritical water as claimed in claim 1, wherein in the ninth step, the supercritical water multi-stage staged fracturing is performed, and the fracturing layer section can be one-stage fracturing or multi-stage fracturing.
8. The multi-stage fracturing method for reducing the fracturing pressure of the hot dry rock reservoir by using the supercritical water as claimed in claim 1, wherein in the ninth step, the supercritical water multi-stage staged fracturing, whether a vertical well, an inclined well or a horizontal well, is performed by sequentially considering the multistage staged fracturing from the bottom of a shaft to the top.
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|---|---|---|---|---|
| CN117780320A (en) * | 2023-12-15 | 2024-03-29 | 中国矿业大学 | Efficient damping dry-hot rock reservoir complex seam net construction method |
| CN117970482A (en) * | 2024-03-28 | 2024-05-03 | 中国地震局地球物理研究所 | Method, system, medium and terminal for judging microseism event dry-wet type |
-
2022
- 2022-12-06 CN CN202211579896.4A patent/CN115853488A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117780320A (en) * | 2023-12-15 | 2024-03-29 | 中国矿业大学 | Efficient damping dry-hot rock reservoir complex seam net construction method |
| CN117780320B (en) * | 2023-12-15 | 2024-05-31 | 中国矿业大学 | Efficient damping dry-hot rock reservoir complex seam net construction method |
| CN117970482A (en) * | 2024-03-28 | 2024-05-03 | 中国地震局地球物理研究所 | Method, system, medium and terminal for judging microseism event dry-wet type |
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