Compressed CO2 energy storage-heat storage method for exhausted oil and gas reservoir based on horizontal well multi-section hydraulic fracture

Abstract

The invention discloses an exhausted oil and gas reservoir compressed CO2 energy storage-heat storage method based on horizontal well multi-section hydraulic fractures, which is applied to the technical field of underground energy storage, and comprises the following steps: carrying out transformation work aiming at an exhausted oil and gas reservoir, carrying out reservoir transformation on an exhausted reservoir without a horizontal well and a hydraulic fracture through horizontal fracturing, and carrying out energy storage and heat storage on the exhausted reservoir without the horizontal well and the hydraulic fracture; forming multiple sections of hydraulic main fractures and communicating with the natural fractures; cO2 is continuously injected into the depleted reservoir through the horizontal well and the hydraulic fracture for padding; the method comprises the following steps: compressing collected CO2 into high-temperature and high-pressure CO2 in a supercritical state in a low ebb of power utilization, injecting the high-temperature and high-pressure CO2 into a depleted reservoir for energy storage, taking the high-pressure CO2 to the ground for expansion power generation in a peak period of power utilization, completing energy release, storing the low-pressure CO2 after energy release in a low-pressure reservoir, not directly discharging, partially sealing and storing, and partially preparing for next circulation to form an energy storage full-chain closed loop. According to the invention, compressed gas energy storage has a larger development space, and becomes another feasible energy storage means after pumped storage.

Description

Technical Field

[0001] The present invention relates to the technical field of underground energy storage, and particularly relates to a method for compressed CO 2 energy storage - heat storage in depleted oil and gas reservoirs based on horizontal well multi - stage hydraulic fractures. Background Technique

[0002] With the continuous expansion of the energy supply - demand gap, there is an urgent need to develop a large - scale energy storage technology to achieve the off - peak utilization of energy. Currently, the main large - scale energy storage technologies are pumped - storage hydroelectricity and compressed - gas geological energy storage systems. Due to the strict site - selection requirements and long construction periods of hydropower stations, pumped - storage hydroelectricity systems cannot meet the continuously growing energy storage demands in the future. Therefore, it is necessary to make full use of the vast underground space, give play to the geographical flexibility and energy storage potential of compressed - gas geological energy storage systems, and promote the construction of MW - level and GW - level energy storage power stations.

[0003] Currently, all successfully commercialized compressed - gas geological energy storage power stations are compressed - air energy storage systems using salt caverns as underground gas storage reservoirs, such as Huntorf Power Station, Jintan Power Station, and Yingcheng Power Station, etc. Salt mine resources are mainly distributed in the eastern region, but the phenomenon of abandoned photovoltaic and wind power is more serious in the western region, and the energy storage demand is more urgent, resulting in geographical limitations of salt - cavern energy storage. In addition, the high - pressure gas compressed on the surface has the characteristic of high temperature at the same time, and salt caverns are not resistant to high temperature. Therefore, the gas needs to be cooled before energy storage to be stored in the salt cavern, and needs to be reheated again before energy release to meet the temperature requirements for expansion. The additional heat - exchange process reduces the system efficiency, resulting in heat - storage temperature limitations of salt - cavern energy storage.

[0004] In terms of energy - storage working fluids, compared with the air used in existing commercial energy storage power stations, CO 2 is easier to liquefy and reach the supercritical state, and has excellent physical properties such as low viscosity and high density. When used for energy storage, its cycle energy consumption is smaller and its energy - storage density is larger, having great energy - storage potential. However, after the compressed CO 2 energy storage system releases energy, the low - pressure CO 2 cannot be directly discharged into the atmosphere, and an additional gas storage tank is required to store the low - pressure CO 2 , increasing the system construction cost. Therefore, at home and abroad, efforts have begun to explore using widely distributed underground natural reservoirs with excellent pressure - bearing performance as gas storage reservoirs for compressed - gas energy storage systems. Using underground reservoirs for compressed - gas energy storage has a wide site - selection range and can reduce the system floor area and cost, which is an important future development direction. However, the seepage resistance of porous media limits the injection - production flow rate of fluids, resulting in higher cycle energy consumption and lower energy - storage efficiency of reservoir compressed - gas energy storage, and it is still in the stage of on - site experimental exploration.

[0005] Therefore, how to provide a compressed gas energy storage technology with greater development space, making it another viable energy storage method after pumped storage, and promoting the construction of a more perfect energy-power system, which is a problem that those skilled in the art urgently need to solve for the compressed CO2 energy storage-heat storage method in depleted oil and gas reservoirs based on horizontal well multi-stage hydraulic fractures. 2 The energy storage-heat storage method is an issue that those skilled in the art urgently need to address. Summary of the Invention

[0006] In view of this, the present invention proposes a compressed CO2 energy storage-heat storage method in depleted oil and gas reservoirs based on horizontal well multi-stage hydraulic fractures.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A compressed CO2 energy storage-heat storage method in depleted oil and gas reservoirs based on horizontal well multi-stage hydraulic fractures, comprising: 2 Step 1: Carry out transformation work on depleted oil and gas reservoirs that do not have production capacity. For depleted reservoirs without horizontal wells and hydraulic fractures, perform reservoir transformation through horizontal fracturing technology to form multi-stage main hydraulic fractures and connect natural fractures, obtaining an ideal fracture network for energy storage. For depleted reservoirs that have already exploited oil and gas resources through horizontal well fracturing technology, directly perform the cushion gas operation in Step 2.

[0009] Step 2: Collect surface CO2 and continuously inject CO2 into the depleted reservoir through horizontal wells and hydraulic fractures for cushion gas. After the cushion gas is completed, enter the cyclic energy storage and release stage in Step 3.

[0010] Step 3: During the low electricity consumption period, drive a compression device with excess electricity and a second preset renewable energy that is difficult to consume in a timely manner to compress the collected CO2 into supercritical high-temperature and high-pressure CO2, and inject it into the depleted reservoir for energy storage. 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 a low-pressure reservoir without direct emission. Partially seal it and prepare for the next cycle. When the working gas volume is insufficient, appropriately supplement it to form a closed loop of the entire energy storage chain. Among them, the energy storage and release stage includes single-stage compression and expansion and multi-stage compression and expansion. 2 and 2 carry out cushion gas injection, and after the cushion gas injection is completed, enter the cyclic energy storage and release stage in Step 3.

[0011] Step 3: During the low electricity consumption period, drive a compression device with excess electricity and a second preset renewable energy that is difficult to consume in a timely manner to compress the collected CO2 into supercritical high-temperature and high-pressure CO2, and inject it into the depleted reservoir for energy storage. 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 a low-pressure reservoir without direct emission. Partially seal it and prepare for the next cycle. When the working gas volume is insufficient, appropriately supplement it to form a closed loop of the entire energy storage chain. Among them, the energy storage and release stage includes single-stage compression and expansion and multi-stage compression and expansion. 2 into supercritical high-temperature and high-pressure CO2 2 and inject it into the depleted reservoir for energy storage. During the high electricity consumption period, take the high-pressure CO2 2 to the ground for expansion power generation to complete energy release, and store the low-pressure CO2 after energy release 2 in a low-pressure reservoir without direct emission, partially seal it and prepare for the next cycle. When the working gas volume is insufficient, appropriately supplement it to form a closed loop of the entire energy storage chain. Among them, the energy storage and release stage includes single-stage compression and expansion and multi-stage compression and expansion.

[0012] Optionally, in Step 1, for depleted reservoirs without horizontal wells and hydraulic fractures, perform reservoir transformation through horizontal fracturing technology to form multi-stage main hydraulic fractures and connect natural fractures, obtaining an ideal fracture network for energy storage, specifically:

[0013] Multiple hydraulic main fractures are formed by hydraulic jet lateral fracturing, and natural fractures are communicated by volume fracturing. Secondary fractures are formed on the side of the hydraulic main fractures, and the secondary fractures continue to branch and extend to form secondary fractures of the second level. After continuous branching and extending, an ideal fracture network for energy storage is finally formed.

[0014] Optionally, in step 2, before injecting CO into the depleted reservoir continuously through the horizontal well and the hydraulic fracture 2 before conducting cushion gas, it further includes:

[0015] heating the CO used as cushion gas by the collected surface waste heat and the first preset renewable energy that is difficult to utilize, so that the difference between the temperature of the cushion gas and the initial temperature of the reservoir is maintained within the preset temperature difference range, and the temperature of the cushion gas is higher than the initial temperature of the reservoir. 2

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

[0017] directly store the compression heat in the depleted reservoir and keep it warm until the energy release stage.

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

[0019] cool the inter-stage compression, store the compression heat of the last stage underground and keep it warm until the energy release stage.

[0020] Optionally, in step 3, the main working area of the gas during the energy storage and release stage is located around the hydraulic fracture and the horizontal well. The cushion gas in the area greater than the preset distance is used to isolate the groundwater for a long time and is permanently stored, realizing the geological storage of CO 2

[0021] According to the above technical solutions, compared with the prior art, the present invention provides a method for compressed CO energy storage and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures of horizontal wells. 2 By using the depleted oil and gas reservoir as the gas storage reservoir of the compressed gas energy storage system, the abandoned underground space and drilling facilities are fully utilized, and the necessary energy storage power is ensured; the hydraulic fracture can reduce the seepage resistance, accumulate highly saturated gas, and extend the service life of the system; the length of the horizontal well is not limited by the reservoir thickness, and it is more convenient to expand the energy storage scale; the compression heat can be directly stored underground and kept warm until the energy release stage, eliminating the combustion chamber and the ground heat exchange device, which helps to improve the efficiency of the energy storage system; CO 2 is used as cushion gas and working gas in a closed-loop manner, so CO 2 the geological storage work can be used as the cushion gas link of the compressed energy storage, giving full play to the technical advantages and improving the economy of energy storage and storage. The present invention improves the integration of resources and technologies, and organically combines CO 2Technical solutions such as geological storage, compressed gas energy storage, underground heat storage, and CCUS enable the compressed gas energy storage technology to have greater development space, making it another viable energy storage means after pumped-storage energy storage and promoting the construction of a more complete energy-power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0023] Figure 1 It is a schematic flowchart of the method of the present invention.

[0024] Figure 2 It is a schematic diagram of compressed CO 2 energy storage - heat storage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0026] Embodiment 1:

[0027] Embodiment 1 of the present invention discloses a method for compressed CO 2 energy storage - heat storage in depleted oil and gas reservoirs based on multi - stage hydraulic fractures in horizontal wells, including:

[0028] Step 1: Carry out transformation work on depleted oil and gas reservoirs that do not have production capacity. Depleted oil and gas reservoirs with a depth of several kilometers have rich drilling data, perfect abandoned well facilities, and good structural traps, which can significantly reduce the transformation cost of gas storage reservoirs in the energy storage system. For depleted reservoirs without horizontal wells and hydraulic fractures, reservoir transformation is carried out through horizontal fracturing technology to form multiple hydraulic main fractures and connect natural fractures, providing an advantageous flow channel for energy storage fluids to obtain an ideal fracture network for energy storage. For depleted reservoirs that have already exploited oil and gas resources through horizontal well fracturing technology, directly perform the cushion gas operation in Step 2.

[0029] For depleted reservoirs without horizontal wells and hydraulic fractures, reservoir transformation is carried out through horizontal fracturing technology to form multiple hydraulic main fractures and connect natural fractures to obtain an ideal fracture network for energy storage. Specifically:

[0030] Multiple hydraulic main fractures are formed through hydraulic jet lateral fracturing, and natural fractures are connected through volume fracturing. Secondary fractures are formed on the side of the hydraulic main fractures, and the secondary fractures continue to branch and extend to form secondary fractures at the second level. Through continuous branching and extension, an ideal fracture network for energy storage is finally formed.

[0031] Compared with the construction cost and cycle of salt caverns, the cost of horizontal well fracturing is lower and the cycle is shorter. Generally, the transformation can be quickly completed and put into production within a few months. The density and length of the main fractures should be reasonably determined according to the reservoir characteristics. In typical sandstone reservoirs and carbonate reservoirs, the length of horizontal wells can range from several hundred meters to several kilometers, the height of hydraulic main fractures is dozens of meters, the length is dozens of meters to two or three hundred meters, the width is 0.5 mm to 1 cm, and the spacing between multiple fractures is 50 meters to more than one hundred meters, mainly depending on the characteristics of the oil and gas reservoir and development technology.

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

[0033] Step 2: Collect surface CO 2 , and continuously inject CO 2 into the depleted reservoir through horizontal wells and hydraulic fractures for cushion gas. The cushion gas will gradually form a large airbag to displace the residual water in the depleted oil and gas reservoir formed by water flooding, fill the reservoir to maintain or even increase the initial reservoir pressure, and provide power for energy release. After the cushion gas is completed, enter the cyclic storage and energy release stage in Step 3.

[0034] Before continuously injecting CO 2 into the depleted reservoir through horizontal wells and hydraulic fractures for cushion gas, it also includes:

[0035] Heat the CO 2 used as cushion gas by the collected surface waste heat and the first preset renewable energy that is difficult to utilize, so that the temperature difference between the cushion gas temperature and the initial reservoir temperature remains within the preset temperature difference range, and the cushion gas temperature is higher than the initial reservoir temperature to avoid too large a temperature difference.

[0036] Step 3: During the low electricity consumption period, drive the compression device with excess electricity and the second preset renewable energy that is difficult to consume in time to compress the collected CO 2 into high-temperature and high-pressure CO 2 in a supercritical state, inject it into the depleted reservoir for energy storage. During the high electricity consumption period, take the high-pressure CO 2 to the ground for expansion power generation to complete energy release, and the low-pressure CO 2Stored in the low-pressure reservoir without direct emission, partially sealed and partially prepared for the next cycle, and appropriately supplemented when the working gas volume is insufficient, forming a closed-loop of the entire energy storage chain; among them, 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] Directly store the compression heat in the depleted reservoir and keep it warm until the energy release stage.

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

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

[0041] Therefore, the energy release gas has an ideal temperature without the need for reheating, eliminating the ground heat exchange device and improving the system efficiency. The target pressure and temperature after compression are determined according to the characteristics of the depleted reservoir. A reservoir with a depth of 2000 meters can withstand a storage pressure of at least 20 MPa and a storage temperature of 100 °C.

[0042] The main working area of the gas during the energy storage and release stage is located around the hydraulic fractures and horizontal wells. The cushion gas in the area greater than the preset distance is used to permanently isolate groundwater and is permanently stored, realizing CO 2 geological storage. Because the hydraulic fracture, as the dominant seepage channel, can help CO 2 to gather around the hydraulic fractures and horizontal wells to form a high-saturation zone. Without hydraulic fractures, CO 2 will float and migrate to the top of the reservoir under the action of buoyancy, resulting in a low gas saturation around the wellbore and the risk that gas and water are produced simultaneously, making the system unable to operate smoothly.

[0043] The compressed CO 2 energy storage - heat storage of the present invention is as Figure 2 shown.

[0044] The embodiment of the present invention discloses a method for compressed CO 2 energy storage - heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures of horizontal wells. By using the depleted oil and gas reservoir as the gas storage reservoir of the compressed gas energy storage system, the abandoned 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 extend the service life of the system; the length of the horizontal well is not limited by the reservoir thickness, and it is more convenient to expand the energy storage scale; the compression heat can be directly stored underground and kept warm until the energy release stage, eliminating the combustion chamber and the ground heat exchange device, which helps to improve the efficiency of the energy storage system; CO 2 is used as cushion gas and working gas in a closed-loop manner, so CO 2As the cushion gas link of compressed energy storage, geological storage work gives full play to technical advantages and improves the economy of energy storage and storage. The present invention improves the integration of resources and technologies, and organically combines technical solutions such as geological storage, compressed gas energy storage, underground heat storage, and CCUS, enabling the compressed gas energy storage technology to have greater development space and becoming another viable energy storage means after pumped storage, thus promoting the construction of a more perfect energy-electricity system. 2 Geological storage, compressed gas energy storage, underground heat storage, and CCUS and other technical solutions, enabling the compressed gas energy storage technology to have greater development space and becoming another viable energy storage means after pumped storage, thus promoting the construction of a more perfect energy-electricity system.

[0045] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.

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

Claims

1. A method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells, characterized in that: include: Step 1: Carry out transformation work for depleted oil and gas reservoirs that do not have production capacity. For depleted reservoirs that do not have horizontal wells and hydraulic fractures, horizontal fracturing technology is used to transform the reservoirs, forming multiple hydraulic main fractures and connecting natural fractures to obtain an ideal fracture network for energy storage. For depleted reservoirs that have been exploited for oil and gas resources through horizontal well fracturing technology, the padding operation in step 2 is directly performed; Step 2: Collect surface CO2, and continuously inject CO2 into the depleted reservoir through the horizontal well and hydraulic fractures for cushioning. After the cushioning is completed, enter the cyclic energy storage and release stage in step 3; Step 3: During the period of low electricity consumption, the collected CO2 is compressed into high-temperature and high-pressure CO2 in a supercritical state by driving a compression device through excess electricity and a second preset renewable energy source that is difficult to consume in time, and injected into the depleted reservoir for energy storage. During the period of peak electricity consumption, the high-pressure CO2 is taken to the ground and expanded to generate electricity, completing energy release, and the low-pressure CO2 after energy release is stored in the low-pressure reservoir instead of being directly discharged, part of which is sealed and part is prepared for the next cycle. When the working gas volume is insufficient, it is appropriately supplemented to form a closed loop of the entire energy storage chain; wherein, the energy storage and release stages include: single-stage compression and expansion and multi-stage compression and expansion.

2. The method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells according to claim 1 is characterized in that: In step 1, the depleted reservoir without horizontal wells and hydraulic fractures is transformed by horizontal fracturing technology to form multiple hydraulic main fractures and connect natural fractures to obtain an ideal fracture network for energy storage, specifically: Multiple hydraulic main fractures are formed by hydraulic jet lateral fracturing, and natural fractures are connected by volume fracturing, and secondary fractures are formed laterally of 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 after continuous branching and extension.

3. The method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells according to claim 1 is characterized in that: In step 2, before continuously injecting CO2 into the depleted reservoir through the horizontal well and the hydraulic fracture for cushioning, the step further includes: The CO2 used as cushion gas is heated by collecting surface waste heat and a first preset renewable energy source that is difficult to utilize, so that the difference between the cushion gas temperature and the initial reservoir temperature is maintained within a preset temperature difference range, and the cushion gas temperature is higher than the initial reservoir temperature.

4. The method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells according to claim 1 is characterized in that: In step 3, the single-stage compression and expansion is specifically as follows: The heat of compression is stored directly in the depleted reservoir and retained until the energy release stage.

5. The method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells according to claim 1 is characterized in that: In step 3, the multi-stage compression and expansion are specifically: Cooling between compression stages stores the heat of compression at the last stage underground and keeps it warm until the energy release stage.

6. The method for compressing CO2 energy and heat storage in depleted oil and gas reservoirs based on multi-stage hydraulic fractures in horizontal wells according to claim 1 is characterized in that: In step 3, the main working area of ​​the gas in the energy storage and release stage is located around the hydraulic fractures and horizontal wells, and the cushion gas in the area greater than the preset distance is used to isolate the groundwater for a long time and is permanently stored to achieve CO2 geological storage.

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