A method for storing energy and heat by compressing co2 in depleted oil and gas reservoirs based on multi-stage hydraulic fractures of horizontal wells

Abstract

The application discloses a kind of depleted oil and gas reservoir compression CO2 energy storage-heat storage method based on horizontal well multi-section hydraulic fracture, applied to underground energy storage technical field, comprising: for depleted oil and gas reservoir, carry out reformation work, for the depleted reservoir without horizontal well and hydraulic fracture, carry out reservoir reformation by horizontal fracturing, form multi-section hydraulic main fracture and communicate natural fracture;Through horizontal well and hydraulic fracture, continuously inject CO2 into depleted reservoir for pad gas;At the low electricity consumption valley, the collected CO2 is compressed into high temperature and high pressure CO2 in supercritical state, and injected into depleted reservoir for energy storage, at the high electricity consumption peak, high pressure CO2 is taken to the ground to expand power generation, complete energy release, and the low pressure CO2 after energy release is stored in low pressure reservoir without direct discharge, part of storage, part of preparation for the next cycle, form energy storage full chain closed loop.The application makes compressed gas energy storage have greater development space, become another feasible energy storage means after pumped storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground energy storage, in particular to a depleted oil and gas reservoir compressed CO2 energy storage-heat storage method based on horizontal well multi-section hydraulic fractures. BACKGROUND

[0002] With the continuous expansion of the energy supply-demand gap, it is urgent to develop a large-scale energy storage technology to realize the peak-shaving utilization of energy. At present, the main large-scale energy storage technologies are pumped storage and compressed gas geological energy storage systems. Due to the strict site selection requirements and long construction period of hydropower stations, the pumped storage system cannot meet the growing energy storage demand in the future. Therefore, it is necessary to make full use of the vast underground space, to give full play to the geographical flexibility and energy storage potential of the compressed gas geological energy storage system, and to promote the construction of MW and GW energy storage power stations.

[0003] At present, all the successfully commercialized compressed gas geological energy storage power stations are compressed air energy storage systems with salt caverns as underground gas storage, such as Huntorf power station, Jintan power station and Yingcheng power station. Salt mine resources are mainly distributed in the eastern region, but the phenomenon of abandoned light and wind in the western region is more serious, and the demand for energy storage is more urgent, resulting in geographical limitations of salt cavern energy storage. In addition, the high-pressure gas after surface compression has high temperature characteristics, and salt caverns are not resistant to high temperature, so the gas needs to be cooled before storage in the salt cavern and heated again before energy release to meet the temperature requirements of expansion. The additional heat exchange process reduces the system efficiency, resulting in temperature limitations of salt cavern energy storage.

[0004] In terms of energy storage working medium, compared with the air used in existing commercial energy storage power stations, CO2 is easier to liquefy and reach a supercritical state, and has excellent properties such as low viscosity and high density, so it has smaller energy consumption and larger energy storage density for energy storage, and has great energy storage potential. However, low-pressure CO2 cannot be directly discharged to the atmosphere after the compressed CO2 energy storage system releases energy, and an additional gas storage tank is needed to store low-pressure CO2, increasing the system construction cost. Therefore, underground natural reservoirs with wide distribution and excellent pressure-bearing performance have been explored as gas storage for compressed gas energy storage systems. The use of underground reservoirs for compressed gas energy storage has a wide range of site selection and can reduce the system footprint and cost, which is an important development direction in the future. However, the seepage resistance of the porous medium limits the injection and production flow rate of the fluid, resulting in higher energy consumption and lower energy storage efficiency of the reservoir compressed gas energy storage cycle, which is still in the field test exploration stage.

[0005] Therefore, how to provide a depleted oil and gas reservoir compressed CO2 energy storage-heat storage method based on horizontal well multi-section hydraulic fractures, which can make the compressed gas energy storage technology have greater development space, become a feasible energy storage means after pumped storage, and promote the construction of a more perfect energy-power system, is a problem that those skilled in the art need to solve. SUMMARY

[0006] In view of the above, the present application provides a depleted oil and gas reservoir compression CO2 energy storage-heat storage method based on horizontal well multi-stage hydraulic fractures.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A depleted oil and gas reservoir compression CO2 energy storage-heat storage method based on horizontal well multi-stage hydraulic fractures, comprising:

[0009] Step 1: For the depleted oil and gas reservoirs without production capacity, carry out modification work, and for the depleted reservoirs without horizontal wells and hydraulic fractures, carry out reservoir modification through horizontal fracturing technology to form multi-stage hydraulic main fractures and communicate natural fractures to obtain an ideal fracture network for energy storage, and for the depleted reservoirs that have been exploited through horizontal well fracturing technology, directly carry out the gas cushioning operation in step 2;

[0010] Step 2: Collect CO2 on the ground and continuously inject CO2 into the depleted reservoir through the horizontal well and the hydraulic fracture for gas cushioning, and after the gas cushioning is completed, enter the cyclic energy storage and release stage in step 3;

[0011] Step 3: During the low electricity consumption period, use the excess electricity and the second predetermined renewable energy that is difficult to timely consume to drive the compression device to compress the collected CO2 into high-temperature and high-pressure CO2 in a supercritical state, and inject it into the depleted reservoir for energy storage, and during the high electricity consumption period, take the high-pressure CO2 to the ground for expansion power generation to complete energy release, and store the low-pressure CO2 after energy release in the low-pressure reservoir without direct discharge, part of which is stored and part of which is prepared for the next cycle, and when the working gas volume is insufficient, it is appropriately supplemented to form a closed loop of the energy storage whole chain; wherein, the energy storage and release stage comprises single-stage compression and expansion and multi-stage compression and expansion.

[0012] Optionally, in step 1, for the depleted reservoirs without horizontal wells and hydraulic fractures, the reservoir modification is carried out through horizontal fracturing technology to form multi-stage hydraulic main fractures and communicate natural fractures to obtain an ideal fracture network for energy storage, specifically:

[0013] A plurality of hydraulic main fractures are formed by hydraulic jet lateral fracturing, and natural fractures are communicated by volume fracturing, secondary fractures are formed laterally in the hydraulic main fractures, the secondary fractures continue to branch and extend to form secondary secondary fractures, and finally an ideal fracture network for energy storage is formed through continuous branching and extension.

[0014] Optionally, in step 2, before continuously injecting CO2 into the depleted reservoir through the horizontal well and the hydraulic fracture for gas cushioning, it further comprises:

[0015] The CO2 as cushion gas is heated by the collected surface waste heat and the first preset renewable energy which is difficult to utilize, so that the temperature difference between the cushion gas and the initial temperature of the reservoir is kept within a preset temperature difference range, and the temperature of the cushion gas is higher than the initial temperature of the reservoir.

[0016] Optionally, in step 3, single-stage compression and expansion, specifically:

[0017] The compression heat is directly stored in the depleted reservoir and is kept warm until the energy release stage.

[0018] Optionally, in step 3, multi-stage compression and expansion, specifically:

[0019] Inter-stage cooling of compression, the compression heat of the last stage is stored underground and kept warm until the energy release stage.

[0020] Optionally, in step 3, the main working area of the gas in the energy storage and release stage is located around the hydraulic fractures and the horizontal well, and the cushion gas in the area greater than the preset distance is used for long-term isolation of underground water and is permanently stored, to realize CO2 geological storage.

[0021] According to the technical scheme, compared with the prior art, the application provides a depleted oil and gas reservoir compression CO2 energy storage and heat storage method based on horizontal well multi-section hydraulic fractures. The depleted oil and gas reservoir is used as a gas storage of the compression gas energy storage system, the underground space and drilling facilities are fully utilized, and the necessary energy storage power is ensured; the hydraulic fractures can reduce the seepage resistance, gather high-saturation gas, and prolong the system operation life; the length of the horizontal well is not limited by the thickness of the reservoir, and the energy storage scale can be more conveniently expanded; the compression heat can be directly stored underground and kept warm until the energy release stage, so that the combustion chamber and the ground heat exchange device are omitted, and the efficiency of the energy storage system is improved; the CO2 is used as the cushion gas and working gas in a closed loop, so that the CO2 geological storage work can be used as the cushion gas link of the compression energy storage, the technical advantages are fully utilized, and the economy of the energy storage and storage is improved. The application improves the integration of resources and technologies, organically combines the CO2 geological storage, compression gas energy storage, underground heat storage and CCUS technical solutions, makes the compression gas energy storage technology have greater development space, becomes another feasible energy storage method after pumped storage, and promotes the construction of a more perfect energy-power system. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical schemes in the embodiments of the application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only embodiments of the application, and other accompanying drawings can be obtained by those skilled in the art without creative labor on the basis of the provided accompanying drawings.

[0023] Figure 1A schematic diagram of the method of the present application.

[0024] Figure 2 A schematic diagram of the compressed CO2 energy storage-heat storage of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0026] Embodiment 1

[0027] Embodiment 1 of the present application discloses a compressed CO2 energy storage-heat storage method for depleted oil and gas reservoirs based on horizontal well multi-stage hydraulic fractures, comprising:

[0028] Step 1: For the depleted oil and gas reservoirs without production capacity, carry out reconstruction work, and the depleted oil and gas reservoirs with a depth of thousands of meters have rich drilling data, perfect abandoned well facilities and good structural traps, which can greatly reduce the reconstruction cost of the gas storage in the energy storage system. For the depleted reservoirs without horizontal wells and hydraulic fractures, carry out reservoir reconstruction through horizontal fracturing technology to form multi-stage hydraulic main fractures and communicate with natural fractures to provide an advantage flow channel for energy storage fluid, and obtain an ideal fracture network for energy storage. For the depleted reservoirs that have been exploited by horizontal well fracturing technology, directly carry out the gas cushioning operation in step 2.

[0029] For the depleted reservoirs without horizontal wells and hydraulic fractures, carry out reservoir reconstruction through horizontal fracturing technology to form multi-stage hydraulic main fractures and communicate with natural fractures to obtain an ideal fracture network for energy storage, specifically:

[0030] Through hydraulic jet lateral fracturing, form multiple hydraulic main fractures, and communicate with natural fractures through volume fracturing, form secondary fractures laterally in the hydraulic main fractures, the secondary fractures continue to branch and extend to form secondary secondary fractures, and finally form an ideal fracture network for energy storage through continuous branching and extension.

[0031] Compared with the construction cost and period of salt caverns, the horizontal well fracturing has lower cost and shorter period, and generally can be quickly completed and put into production in a few months. The main fracture density and length should be reasonably determined according to the reservoir characteristics. In typical sandstone reservoirs and carbonate reservoirs, the horizontal well length can be between a few hundred meters and a few thousand meters, the hydraulic main fracture has a height of tens of meters, a length of tens of meters to two or three hundred meters, a width of 0.5 millimeters to 1 centimeter, and a multi-stage fracture interval of 50 meters to more than 100 meters, which mainly depends on the characteristics of the oil and gas reservoirs and the development technology.

[0032] Horizontal wells can be more convenient to increase length and expand the scale of energy storage; while the traditional vertical well system is limited by reservoir thickness, the well length is usually about 100 meters, and the injection and production capacity is usually tens of kilograms per second, which is difficult to meet the hundreds of kilograms per second of energy storage demand of commercial energy storage power stations.

[0033] Step 2: Collecting CO2 from the surface and continuously injecting CO2 into the depleted reservoir through horizontal wells and hydraulic fractures to pad gas, which will gradually form a large gas pocket, displace the residual water in the depleted oil and gas reservoir formed by water flooding, and fill the reservoir to maintain or even increase the initial reservoir pressure to provide power for energy release. After the padding gas is completed, it enters the circulating energy storage and release stage in step 3.

[0034] Before continuously injecting CO2 into the depleted reservoir through horizontal wells and hydraulic fractures to pad gas, it also includes:

[0035] Heating the CO2 used as padding gas by collecting surface waste heat and the first preset renewable energy that is difficult to utilize, so that the difference between the padding gas temperature and the initial reservoir temperature is maintained within a preset temperature difference range, and the padding gas temperature is higher than the initial reservoir temperature, to avoid excessive temperature difference.

[0036] Step 3: During the low electricity consumption period, use excess electricity and the second preset renewable energy that is difficult to timely absorb to drive the compression device to compress the collected CO2 into high-temperature and high-pressure CO2 in a supercritical state, and inject it into the depleted reservoir for energy storage. During the electricity consumption peak period, take the high-pressure CO2 to the ground for expansion power generation to complete energy release, and store the low-pressure CO2 after energy release in the low-pressure reservoir without direct discharge, part of which is stored and part of which is prepared for the next cycle. When the working gas volume is insufficient, appropriate supplement is made to form a closed loop of the entire energy storage chain; wherein, the energy storage and release stage includes: single-stage compression and expansion and multi-stage compression and expansion.

[0037] Single-stage compression and expansion, specifically:

[0038] The compression heat is directly stored in the depleted reservoir and is kept warm until the energy release stage.

[0039] Multi-stage compression and expansion, specifically:

[0040] Inter-stage cooling of compression, storing the last stage of compression heat in the underground and keeping it warm until the energy release stage.

[0041] Therefore, the energy release gas has an ideal temperature without the need for further heating, eliminating the need for a ground heat exchange device, and the system efficiency is improved. The target pressure and temperature after compression are determined according to the characteristics of the depleted reservoir. A 2000-meter-deep reservoir can withstand at least 20 MPa of storage pressure and 100℃ of storage temperature.

[0042] The main working area of the gas in the storage and release energy stage is located around the hydraulic fracture and the horizontal well, and the cushion gas in the area greater than the preset distance is used for long-term isolation of underground water and is permanently stored to achieve CO2 geological storage. Because the hydraulic fracture can help CO2 to gather around the hydraulic fracture and the horizontal well to form a high saturation area as an advantage seepage channel. Without the hydraulic fracture, CO2 will migrate to the top of the reservoir under the action of buoyancy, resulting in low gas saturation around the well, and there is a risk that gas and water will be produced simultaneously, which makes the system unable to work smoothly.

[0043] The compressed CO2 energy storage and heat storage of the present application is shown as Figure 2 .

[0044] The embodiment of the present application discloses a compressed CO2 energy storage and heat storage method based on a horizontal well multi-section hydraulic fracture in a depleted oil and gas reservoir. By taking the depleted oil and gas reservoir as a gas storage of a compressed gas energy storage system, the underground space and drilling facilities are fully utilized, and the necessary energy storage power is ensured; the hydraulic fracture can reduce the seepage resistance, gather high-saturation gas, and prolong the service life of the system; the length of the horizontal well is not limited by the thickness of the reservoir, and the energy storage scale can be more conveniently expanded; the compressed heat can be directly stored underground and insulated to the energy release stage, so that the combustion chamber and the ground heat exchange device are saved, which helps to improve the efficiency of the energy storage system; CO2 is used as the cushion gas and working gas in a closed loop, so that the CO2 geological storage work can be used as the cushion gas link of the compressed energy storage, the technical advantages are fully utilized, and the economy of the energy storage and storage is improved. The integration of resources and technologies is improved, and the technical solutions of CO2 geological storage, compressed gas energy storage, underground heat storage and CCUS are organically combined, so that the compressed gas energy storage technology has greater development space, becomes another feasible energy storage means after pumped storage, and promotes the construction of a more perfect energy-power system.

[0045] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0046] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for storing energy and heat by compressing CO2 in depleted oil and gas reservoirs based on multiple hydraulic fractures of horizontal wells, characterized in that, The method comprises the following steps: Step 1: Reservoir reconstruction is carried out on a depleted oil and gas reservoir without horizontal wells and hydraulic fractures, and a multi-stage hydraulic main fracture is formed by horizontal fracturing technology to communicate with natural fractures, so that an ideal fracture network for energy storage is obtained; and a gas cushioning operation is directly carried out on a depleted reservoir which has been exploited by horizontal well fracturing technology in step 2; Step 2: Collecting CO2 on the ground, and continuously injecting CO2 into the depleted reservoir through the horizontal well and the hydraulic fracture for gas cushioning, and then entering the energy storage and release cycle in step 3; Step 3: During the low power consumption period, the collected CO2 is compressed into high-temperature and high-pressure CO2 in a supercritical state by using excess power and the second preset renewable energy source which is difficult to be timely consumed to drive a compression device, and then the high-temperature and high-pressure CO2 is injected into the depleted reservoir for energy storage; during the high power consumption period, the high-pressure CO2 is taken to the ground to expand and generate power, and the energy is released; and the low-pressure CO2 after the energy release is stored in a low-pressure reservoir without being directly discharged, part of the low-pressure CO2 is permanently stored and part of the low-pressure CO2 is prepared for the next cycle, and the working gas amount is appropriately supplemented when the working gas amount is insufficient, so that a closed loop of the energy storage whole chain is formed; wherein, the energy storage and release cycle comprises single-stage compression and expansion and multi-stage compression and expansion; Before the CO2 is continuously injected into the depleted reservoir through the horizontal well and the hydraulic fracture for gas cushioning in step 2, the method further comprises the following steps: The CO2 for gas cushioning is heated by using the collected ground waste heat and the first preset renewable energy source which is difficult to be utilized, so that the temperature difference between the gas cushioning temperature and the initial temperature of the reservoir is kept within a preset temperature difference range, and the gas cushioning temperature is higher than the initial temperature of the reservoir.

2. The method of claim 1, wherein the method is a method of CO2 storage and energy-heat storage compression in depleted oil and gas reservoirs based on multi-stage hydraulic fractures of horizontal wells. In step 1, the depleted reservoir without horizontal wells and hydraulic fractures is reconstructed by horizontal fracturing technology, a multi-stage hydraulic main fracture is formed to communicate with natural fractures, and an ideal fracture network for energy storage is obtained, and the method specifically comprises the following steps: A plurality of hydraulic main fractures are formed by hydraulic jetting lateral fracturing, and natural fractures are communicated by volume fracturing, secondary fractures are formed laterally in the hydraulic main fractures, the secondary fractures continue to branch and extend to form secondary fractures of the second level, and finally an ideal fracture network for energy storage is formed through continuous branching and extension.

3. The method of claim 1, wherein the method is a method of CO2 storage and energy-heat storage compression in depleted oil and gas reservoirs based on multi-stage hydraulic fractures of horizontal wells. In step 3, the single-stage compression and expansion specifically comprises the following steps: The compression heat is directly stored in the depleted reservoir and is kept warm until the energy release stage.

4. The method of claim 1, wherein the method is a method of CO2 storage and energy-heat storage compression in depleted oil and gas reservoirs based on multiple hydraulic fractures of horizontal wells. In step 3, the multi-stage compression and expansion specifically comprises the following steps: The compression heat is stored in the ground and kept warm until the energy release stage through inter-stage cooling.

5. The method of claim 1, wherein the method is a method of CO2 storage and energy-heat storage compression in depleted oil and gas reservoirs based on multiple hydraulic fractures of horizontal wells. In step 3, the main working area of the gas in the energy storage and release cycle is located around the hydraulic fracture and the horizontal well, and the gas cushioning in a region greater than a preset distance is used to isolate underground water for a long time and is permanently stored, so that CO2 geological storage is realized.

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