Method for transforming exhausted or nearly exhausted unconventional oil and gas reservoir into compressed air energy storage system

Abstract

The invention discloses a method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system, which is applied to the technical field of underground energy storage and aims to solve the problem that the existing main compressed air energy storage system is mainly a salt cavern reservoir, but salt caverns capable of being used for compressed air energy storage are insufficient from comprehensive factors. According to the invention, an existing exhausted or nearly exhausted unconventional oil and gas reservoir is transformed as an energy storage place for compressed air. Due to the fact that the exhausted or nearly exhausted unconventional oil gas fracturing well is adopted, the existing fracturing well can be effectively utilized, resource waste is avoided, and economic benefits are increased. Due to the fact that the complex fracture network space formed by fracturing and the pore space, disturbed by fracturing, of the unconventional oil and gas reservoir are utilized, high-pressure gas can be effectively sealed, leakage is reduced, and the pressure maintaining capacity is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground energy storage, and in particular relates to a compressed air energy storage technology. Background Art

[0002] The use of fossil energy has brought serious environmental problems. In order to meet the goals of "carbon peak" and "carbon neutrality", it is necessary to vigorously develop renewable energy. Renewable energy includes wind energy, solar energy, hydropower, biomass energy, wave energy, tidal energy, ocean temperature difference energy and geothermal energy. The geographical and seasonal fluctuations of renewable energy, as well as its unstable characteristics, pose challenges to energy supply. Energy storage technology plays a key role in this situation, which can help make up for the mismatch between energy supply and demand, improve energy utilization efficiency, and promote the large-scale application of renewable energy. Compressed gas energy storage technology has become a better energy storage option because of its low site selection restrictions, high economic benefits, and stable safety. At present, the main compressed gas energy storage system is mainly salt cavern reservoirs, but from a comprehensive perspective, the salt caverns that can be used for compressed gas energy storage are insufficient. Summary of the invention

[0003] In order to supplement geological bodies that can be used as compressed air energy storage sites, the present invention provides a method for transforming depleted or nearly depleted unconventional oil and gas reservoirs into a compressed air energy storage system.

[0004] The technical solution adopted by the present invention is: a method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system, comprising:

[0005] S1. Select appropriate depleted or nearly depleted unconventional oil and gas reservoir fracturing wells as energy storage wells;

[0006] S2. The wellbore of the energy storage well selected in step S1 is located at one end of the wellhead and connected to the compressor output end and the expander input end through valves;

[0007] The compressor is electrically connected to the motor, the motor is connected to a circuit for outputting electric energy from a power grid or a renewable energy source, and the compressor works under the drive of the motor;

[0008] The output end of the expander is connected to a generator, and the generator generates electric energy under the drive of the high-pressure gas output by the expander; the generator is connected to the power grid;

[0009] S3, when storing energy, the motor drives the compressor to compress the air into the energy storage well for energy storage;

[0010] S4. When generating electricity, the principle of internal and external pressure difference is used to release the high-pressure gas in the energy storage well to drive the generator to generate electricity.

[0011] Beneficial effects of the present invention: The present invention provides a new compressed air energy storage site, supplements the geological bodies that can be used for compressed air, improves the utilization rate of renewable energy, and alleviates energy fluctuations. Existing depleted or nearly depleted unconventional oil and gas reservoirs can be transformed as compressed air energy storage sites. Since depleted or nearly depleted unconventional oil and gas fracturing wells are used, existing fracturing wells can be effectively utilized, avoiding waste of resources and increasing economic benefits. Since the complex fracture network space formed by fracturing and the pore space of the unconventional oil and gas reservoir disturbed by fracturing are utilized, high-pressure gas can be effectively sealed, leakage can be reduced, and the pressure holding capacity can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a flow chart of the method of the present invention;

[0013] Figure 2 This is a schematic diagram of a shale gas fracturing single well transformation well;

[0014] Figure 3 Schematic diagram of a storage well converted from a fracturing well in a shale gas fracturing platform;

[0015] Figure 4 Schematic diagram of the energy storage well transformed from a fracturing well in a shale gas multi-fracturing platform. DETAILED DESCRIPTION

[0016] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0017] like Figure 1 As shown, the present invention provides a method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed gas energy storage site, which mainly comprises the following steps:

[0018] 1. Select appropriate depleted or nearly depleted unconventional oil and gas reservoir fracturing wells as energy storage wells;

[0019] 2. Laying of lines to connect electricity generated by renewable energy;

[0020] 3. Add motors and compressors to the ground facilities to compress the air, and add expanders and generators to generate electricity. Specifically: the motor is connected to the circuit connected to the renewable energy output electricity and is connected to the compressor. The motor drives the piston or rotating parts of the compressor to compress the air to a higher pressure. The compressed high-pressure air is input into the wellbore through the pipeline, and a valve is installed at the wellhead. It is opened when the high-pressure air is input and closed for storage after the input. A pressure gauge is also installed at the wellhead to measure the pressure of the compressed air in the energy storage well. In actual application, during the storage process, when the pressure value measured by the compressed air in the energy storage well reaches the minimum horizontal principal stress corresponding to the energy storage well, it means that the maximum storage capacity of the energy storage well has been reached, and the valve is closed to stop the storage of compressed air.

[0021] Those skilled in the art should know that the minimum horizontal principal stress corresponding to the energy storage well mentioned here has been measured during the early fracturing process of the energy storage well, and the specific measurement process of the minimum horizontal principal stress corresponding to the energy storage well is not described in detail in the present invention.

[0022] 4. Laying of lines to transmit the electricity generated by the release of high pressure gas.

[0023] Depleted or nearly depleted unconventional oil and gas reservoirs are compressed gas energy storage sites. The main steps are as follows:

[0024] 1. When renewable energy generates excess electricity, collect the excess electricity generated by renewable energy;

[0025] 2. Use excess electrical energy to drive motors and compressors to compress air into energy storage wells;

[0026] 3. When the demand for electricity is large, the high-pressure gas is released from the energy storage well by using the principle of internal and external pressure difference; and the release rate of the high-pressure gas is controlled by controlling the valve;

[0027] The specific bleed timing and power requirements will vary depending on system design and application.

[0028] The Compressed-Air Energy Storage (CAES) system will start to discharge gas when the power demand reaches 70%-90% of its designed capacity to ensure grid stability. For example, if the maximum discharge capacity of a CAES system is 100MW, when the grid demand reaches 70-90MW, the system will start to discharge gas to meet the demand.

[0029] These values ​​depend on the specific energy storage system configuration and the load demand of the power grid.

[0030] 4. High-pressure gas generates electricity through a turbo expander and generator;

[0031] 5. The generated electricity is transmitted to where it is needed through the laid circuits.

[0032] Of course, the energy storage process can also be carried out when the power consumption of the power grid is at a low point, using excess electricity to drive motors and compressors to compress air into energy storage wells for energy storage.

[0033] Selecting a suitable fracturing well for depleted or nearly depleted unconventional oil and gas reservoirs requires the following four conditions: mechanical stability, low permeability, small heat transfer coefficient, and high fracture toughness. These four conditions are explained below:

[0034] Mechanical stability:

[0035] To screen the reservoir, select rocks that are consistent with the target reservoir, or drill rocks on the target reservoir, and process 6 standard samples with a diameter of 50 mm and a height of 100 mm to carry out cyclic loading and unloading experiments.

[0036] Triaxial compression mechanics tests were carried out on three of the standard samples at reservoir temperature and confining pressure to obtain the triaxial compressive strength of the standard samples.

[0037] Cyclic loading and unloading mechanical tests were carried out on the other three standard samples at reservoir temperature and confining pressure, and the upper and lower limits of stress were set to 50% and 10% of the triaxial compressive strength, respectively.

[0038] If the number of cycles of the standard sample of three cycles of loading and unloading exceeds 1000 times, the selected reservoir can be considered to be a mechanically stable unconventional reservoir.

[0039] Low penetration:

[0040] To screen the reservoir, select rocks that are consistent with the target reservoir, or drill rocks on the target reservoir, and process three standard samples with a diameter of 25 mm and a height of 50 mm for permeability experiments.

[0041] The permeability test was performed on three standard samples. If the average permeability was lower than 0.5×10 -3 μm 2 , which can be considered as an unconventional reservoir with low permeability.

[0042] Small heat transfer coefficient:

[0043] To screen the reservoir, select rocks that are consistent with the target reservoir, or drill rocks on the target reservoir, and process three standard samples with a diameter of 2 mm and a thickness of 2 mm for heat transfer experiments.

[0044] Heat transfer experiments were conducted on three standard samples. If the average heat transfer coefficient obtained was lower than 1W / m 2 ·K (W / (m2·degree)), which can be considered as an unconventional reservoir with a small heat transfer coefficient.

[0045] High fracture toughness

[0046] To screen the reservoir, select rocks that are consistent with the target reservoir, or drill rocks on the target reservoir, and process three standard samples of 40 × 10 × 10 mm for fracture toughness tests.

[0047] The fracture toughness test was carried out on three standard samples. If the fracture toughness obtained was lower than 1 MPa·m1 / 2, it could be considered as an unconventional reservoir with high fracture toughness.

[0048] Example 1

[0049] The method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system comprises the following steps:

[0050] The depleted or nearly depleted unconventional oil and gas reservoirs selected are shale gas reservoirs. Figure 2 The shale gas fracturing single well transformation well shown. Since the fracturing well produces shale gas, the shale gas does not leak into the formation, so when the compressed air enters the energy storage well, it will not leak into the formation either, and has the ability to store high-pressure gas.

[0051] When electricity demand is low, excess electricity from renewable energy sources such as solar or wind energy is used to compress air into storage wells through motors and compressors, and high-pressure gas is stored in the complex fracture network space formed by fracturing and the pore space of unconventional oil and gas reservoirs disturbed by fracturing.

[0052] When electricity consumption is at its peak, high-pressure gas is released from the energy storage well, which drives the turbo expander and generator to generate electricity, which is then transmitted to places with high electricity demand.

[0053]

[0054] w e Electric energy generated, m e Mass flow rate during deflation, c p is the constant pressure specific heat of air, are the temperatures entering and leaving the expander, respectively.

[0055] Example 2

[0056] The method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system comprises the following steps:

[0057] The depleted or nearly depleted unconventional oil and gas reservoirs selected are shale gas reservoirs. Figure 3The fracturing well in the shale gas fracturing platform shown is transformed into a storage well. Since the fracturing well produces shale gas, the shale gas does not leak into the formation, so when the compressed air enters the storage well, it will not leak into the formation either, and has the ability to store high-pressure gas.

[0058] When electricity demand is low, excess electricity from renewable energy sources such as solar or wind energy is used to compress air into storage wells through motors and compressors, and high-pressure gas is stored in the complex fracture network space formed by fracturing and the pore space of unconventional oil and gas reservoirs disturbed by fracturing.

[0059] When electricity consumption is at its peak, high-pressure gas is released from the energy storage well, which drives the turbo expander and generator to generate electricity, which is then transmitted to places with high electricity demand.

[0060] Example 3

[0061] The method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system comprises the following steps:

[0062] The depleted or nearly depleted unconventional oil and gas reservoirs selected are shale gas reservoirs. Figure 4 The fracturing wells in the shale gas multi-fracture platform shown are transformed into energy storage wells. Since the fracturing wells produce shale gas, the shale gas does not leak into the formation, so when the compressed air enters the energy storage well, it will not leak into the formation either, and has the ability to store high-pressure gas.

[0063] When electricity demand is low, excess electricity from renewable energy sources such as solar or wind energy is used to compress air into storage wells through motors and compressors, and high-pressure gas is stored in the complex fracture network space formed by fracturing and the pore space of unconventional oil and gas reservoirs disturbed by fracturing.

[0064] When electricity consumption is at its peak, high-pressure gas is released from the energy storage well, which drives the turbo expander and generator to generate electricity, which is then transmitted to places with high electricity demand.

[0065] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the unconventional oil and gas reservoirs may be tight sandstone, shale, tight oil, shale oil or other unconventional oil and gas reservoirs that use hydraulic fracturing as the main method for increasing production.

[0066] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the renewable energy is solar energy, wind energy or other renewable energy in the region.

[0067] According to the above aspects and any possible implementation, an implementation is further provided, wherein the fracturing well may be a single well, multiple wells in a fracturing well platform, or multiple fracturing well platforms.

[0068] Renewable energy is solar energy, wind energy or other renewable energy sources in the area.

[0069] The function of the valve in this embodiment is explained as follows: when injecting gas, open the valve connecting the wellhead and the compressor, and close the valve connecting the wellhead and the expander; when exhausting gas, open the valve connecting the wellhead and the expander, and close the valve connecting the wellhead and the compressor.

[0070] In this embodiment, a regulating valve is used to control the gas flow rate. By adjusting the opening of the regulating valve, the amount of air flowing through the pipeline can be accurately controlled; in specific applications, a flow regulator or a pressure regulator can be selected. The flow regulator is usually integrated into the air system and the release rate is controlled by setting the flow rate; the pressure regulator controls the pressure in the system, thereby indirectly controlling the gas flow rate. The pressure regulator maintains the system pressure at a set value, and the flow rate changes with the pressure and pipeline resistance.

[0071] Combining flow sensors and automatic control systems can achieve real-time flow monitoring and adjustment. The flow sensor monitors the gas flow data, and the control system adjusts the valve or regulator based on this data to maintain the expected flow.

[0072] Use a preset switch to control the gas flow. When the flow reaches the set value, the switch will trigger and adjust or shut off the gas release accordingly.

[0073] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system, characterized in that: include: S1. Select appropriate depleted or nearly depleted unconventional oil and gas reservoir fracturing wells as energy storage wells; S2. The wellbore of the energy storage well selected in step S1 is located at one end of the wellhead and connected to the compressor output end and the expander input end through valves; The compressor is electrically connected to the motor, the motor is connected to a circuit for outputting electric energy from a power grid or a renewable energy source, and the compressor works under the drive of the motor; The output end of the expander is connected to a generator, and the generator generates electric energy under the drive of the high-pressure gas output by the expander; the generator is connected to the power grid; S3, when storing energy, the motor drives the compressor to compress the air into the energy storage well for energy storage; S4. When generating electricity, the principle of internal and external pressure difference is used to release the high-pressure gas in the energy storage well to drive the generator to generate electricity.

2. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 1, characterized in that: In step S1, a suitable depleted or nearly depleted unconventional oil and gas reservoir fracturing well is selected based on mechanical stability, permeability, heat transfer coefficient, and fracture toughness.

3. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 2, characterized in that: The specific requirements for mechanical stability are: A1. Select rocks consistent with the target reservoir and process them into several first standard samples with a diameter of 50 mm and a height of 100 mm; A2. Performing triaxial compression mechanics tests at reservoir temperature and confining pressure on at least three of the first standard samples to obtain the triaxial compressive strength of the first standard samples; A3, performing a cyclic loading and unloading mechanical test at reservoir temperature and confining pressure on the remaining first standard samples, and setting upper and lower limits of stress according to the triaxial compressive strength obtained in step A2; A4. If the number of cycles of the first standard sample of these cyclic loading and unloading exceeds the preset number, the reservoir is considered to be an unconventional reservoir that meets the mechanical stability requirements.

4. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 3, characterized in that: The specific requirements for permeability are: Select rocks consistent with the target reservoir and process at least three second standard samples with a diameter of 25 mm and a height of 50 mm; The second standard samples were tested for permeability. If the average permeability was less than 0.5×10 -3 μm 2 , it is considered to be an unconventional reservoir that meets the permeability requirements.

5. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 4, characterized in that: The specific requirements for heat transfer coefficient are: Select rocks consistent with the target reservoir and process at least three third standard samples with a diameter of 2 mm and a thickness of 2 mm; Heat transfer experiments are carried out on these third standard samples. If the average heat transfer coefficient obtained is lower than 1W / m 2 ·K, it is considered to be an unconventional reservoir that meets the heat transfer coefficient requirements.

6. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 5, characterized in that: The specific requirements for fracture toughness are: Select rocks consistent with the target reservoir and process at least three fourth standard samples with a size of 40×10×10 mm; The fourth standard samples are subjected to a fracture toughness test. If the fracture toughness obtained is lower than 1 MPa·m1 / 2, it is considered to be an unconventional reservoir that meets the fracture toughness requirement.

7. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 6, characterized in that: The complex fracture network space formed by fracturing in energy storage wells and the pore space of unconventional oil and gas reservoirs disturbed by fracturing are used to store high-pressure gas.

8. A method for transforming a depleted or nearly depleted unconventional oil and gas reservoir into a compressed air energy storage system according to claim 7, characterized in that: The unconventional oil and gas reservoir fracturing well is one of: a shale gas fracturing single well, a fracturing well in a shale gas fracturing platform, and a fracturing well in a shale gas multi-fracturing platform.

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