Method and system for storing and releasing energy by utilizing foam

Abstract

The invention belongs to the technical field of underground energy storage, and particularly relates to a method and system for storing and releasing energy through foam, and the method comprises the steps that S1, at least one target stratum fracture is selected; s2, high-pressure foam fluid is injected into the at least one target stratum fracture, so that the pressure of the at least one target stratum fracture is increased, and the fracture width is increased; therefore, the electric energy is converted into elastic deformation energy of stratum rock and compression energy of gas in foam to be stored; and S3, high-pressure fluid reversely discharged from a wellhead in the closing process of at least one target stratum fracture is utilized, and corresponding power generation equipment is driven to generate power according to the state of the high-pressure fluid so as to release energy. According to the method and the system, the effective energy storage density of the formation fracture can be greatly improved, and energy consumed by gravitational potential energy increase in the fluid reverse discharge process is reduced; the energy storage method is low in investment and maintenance cost, can adapt to different earth terrains, and is wide in application range.

Description

Technical Field

[0001] The present invention relates to the technical field of underground energy storage, and in particular to a method and system for storing and releasing energy using foam. Background Art

[0002] Many renewable energy sources, such as solar and wind, have daily and seasonal intermittent output, making their power output unstable. Therefore, how to store excess clean electricity on a large scale and reliably transmit it when sunlight and wind are insufficient remains a technical challenge that countries around the world are tackling.

[0003] Underground energy storage technology is a key approach to addressing the volatility of renewable energy and the need for long-term energy storage. It is particularly suitable for emerging power systems with a high proportion of renewable energy. It primarily utilizes underground spaces (such as salt caverns, abandoned mines, aquifers, or rock formations) to store energy media (such as compressed air, hydrogen, heat, or liquids) to achieve large-scale, long-term energy storage and release. This technology is primarily used to balance electricity supply and demand, improve renewable energy utilization, and support grid stability.

[0004] Chinese patent document CN114016988A discloses a method and system for storing and releasing energy through formations. The method performs hydraulic fracturing in an energy storage formation that does not contain oil or gas, thereby generating at least one formation fracture. High-pressure fluid is then injected into the resulting formation fracture to cause elastic deformation of the formation fracture to store energy. The energy is then released by discharging the high-pressure fluid in the fracture back into a preset power generation device.

[0005] This method can use high-pressure liquid fluids to store energy (such as water). However, using high-pressure liquid fluids to store energy will severely limit the energy storage density and output power of this method. On the one hand, the backflow of high-pressure fluids from the wellbore will convert the stored energy into the gravitational potential energy of water (the energy consumed by water moving from the depth of the formation to the surface). In shallow fracture energy storage systems, such as those within a depth of 500 meters, nearly 50% of the energy in the fracture reservoir is used to convert into the gravitational potential energy of water, and only nearly 50% is used for power generation. On the other hand, due to the limitation of the wellbore diameter, the output power of energy storage using high-pressure liquid fluids is only 1-3MW, which severely limits the application scenarios of this method.

[0006] This method can utilize high-pressure gas fluids (such as air) for energy storage. Since the density of air is much smaller than that of liquid, only a small portion of the compressed air discharged from the fracture energy storage system is converted into the gravitational potential energy of the air. At the same time, since the gas has a greater flow rate in the pipeline and the compression energy it carries, the output power of energy storage using high-pressure gas fluids is greatly improved. However, the cost of compressing high-pressure gas to increase the gas pressure is much greater than the cost of increasing the liquid fluid pressure. For example, to compress air to increase the pressure and inject it into the wellbore, a multi-stage compressor is usually required for pressurization. At the same time, a large amount of heat is generated during the air compression process, requiring a matching heat treatment and heat recovery system, which sharply increases the investment cost of ground equipment, and the subsequent operation and maintenance costs are also very high.

[0007] Chinese patent document CN 118654399 A discloses a method and system for storing and releasing energy through formation fractures and obtaining geothermal energy. The system includes a fracturing device for pumping fracturing fluid into a wellbore to create formation fractures in the energy storage geothermal layer; an injection pipeline connected to an injection device; a backflow pipeline connected to a hydroelectric power generation device, a geothermal power generation device, and a heating system, so that when the fluid in the formation fracture is reversed through the backflow pipe, it can drive the hydroelectric power generation device and the geothermal power generation device to generate electricity and provide heating through the heating system; and a plugging device for closing the backflow pipeline so that the fluid in the formation fracture continuously exchanges heat with the energy storage geothermal layer, causing the fluid temperature to continue to rise. This technical solution is to construct a formation fracture in a geothermal layer with geothermal resources, and then inject a normal temperature high-pressure fluid, such as a liquid, to increase the width of the formation fracture, causing the formation rock to elastically deform and store energy. Therefore, this technical solution is highly dependent on geological conditions, limiting its applicability. It is not suitable for plains, geologically unstable areas, or areas without geothermal resources. Furthermore, the efficiency of energy storage based solely on elastic deformation is low. Energy is lost during the storage and release of rock elastic deformation energy, and a large portion of the released energy is converted into gravitational potential energy of water. Furthermore, the efficiency of heat exchange between the fluid and the formation in this method is affected by the fracture extension radius and the duration of closed heat storage. If the wellbore outlet temperature is insufficient (e.g., below 50°C), the method can only be used for heating, not power generation.

[0008] Therefore, there is an urgent need for a new clean electricity storage method with low investment and maintenance costs, high electricity conversion efficiency in formation energy storage, and adaptability to various terrains. Summary of the Invention

[0009] The purpose of the present invention is to provide a method and system for storing and releasing energy using foam, which can partially solve or alleviate the above-mentioned shortcomings in the prior art, significantly increase the effective energy storage density in formation fractures, and reduce the energy consumed by the gravitational potential energy during fluid backflow; at the same time, the energy storage method has low investment and maintenance costs, can adapt to different surface terrains, and has a wide range of applications.

[0010] In order to solve the above-mentioned technical problems, the present invention specifically adopts the following technical solutions: A first aspect of the present invention is to provide a method for storing and releasing energy using foam, which specifically comprises the following steps: S1: selecting at least one target formation fracture that does not contain oil or gas; preferably, the target formation fracture is connected to only one wellbore through the formation; S2: injecting high-pressure foam fluid into at least one of the target formation fractures, thereby increasing the pressure of the at least one target formation fracture and widening the fracture; thereby converting the electrical energy into elastic deformation energy of the formation rock and compression energy of the gas in the foam for storage; That is, electrical energy is converted into elastic potential energy generated by the deformation of stratum rock for storage; and storing the potential energy of the compressed air caused by the pressure increase in the space of the target formation fracture due to the gas in the foam; S3: utilizing the high-pressure fluid discharged from the wellhead during the closing process of at least one of the target formation fractures, and driving corresponding power generation equipment to generate electricity according to the state of the high-pressure fluid to release energy; In step S3, after detecting that there is a demand for power generation, the state of the high-pressure fluid to be discharged is first determined during the closing process. The state of the high-pressure fluid is divided into high-pressure gas fluid, high-pressure liquid fluid and high-pressure foam fluid; When the reversed high-pressure fluid is in a gaseous state, i.e., a high-pressure gas fluid, the reversed high-pressure gas fluid is first used to drive the preset gas power generation equipment to generate electricity; After the high-pressure gas fluid in the wellbore and the target formation fracture is emptied, the remaining high-pressure liquid fluid is reversely discharged, thereby driving the preset liquid power generation equipment to generate electricity; When the high-pressure fluid discharged from the wellhead during the closing process is high-pressure foam fluid, the discharged high-pressure foam fluid is first transported to the separation device for gas-liquid separation, and then the high-pressure liquid fluid and high-pressure gas fluid obtained after separation are used to drive their respective preset corresponding power generation equipment to generate electricity.

[0011] Preferably, in step S3, the state of the high-pressure fluid discharged from the wellhead is determined by monitoring the pressure of the high-pressure fluid in the wellhead or wellbore, or / and the density of the high-pressure fluid, or / and the dielectric constant of the high-pressure fluid, or / and the propagation speed of sound waves in the high-pressure fluid; accordingly, If the density of the high-pressure fluid is less than a first preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the density of the high-pressure fluid is greater than a second preset density threshold and less than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; If the density of the high-pressure fluid is greater than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid; Wherein, the first preset density threshold is smaller than the second preset density threshold, and the second preset density threshold is smaller than the third preset density threshold; or, If the dielectric constant of the high-pressure fluid is less than a first preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the dielectric constant of the high-pressure fluid is greater than a second preset dielectric threshold and less than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; If the dielectric constant of the high-pressure fluid is greater than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid; The first preset dielectric threshold is smaller than the second preset dielectric threshold, and the second preset dielectric threshold is smaller than the third preset dielectric threshold; or, If the propagation speed of the sound wave in the high-pressure fluid is less than a first preset sound speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the sound wave propagation speed in the high-pressure fluid is greater than a second preset sound speed threshold and less than a third preset sound speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; Wherein, the first preset sound speed threshold is smaller than the second preset sound speed threshold, and the second preset sound speed threshold is smaller than the third preset sound speed threshold; If the acoustic wave propagation speed of the high-pressure fluid is greater than a third preset acoustic speed threshold, it is determined that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid fluid.

[0012] Because the foamy state cannot be directly used for power generation and energy release, the state of the high-pressure fluid discharged from the wellhead must be determined. If it is foamy, it must first be separated into gas and liquid through a separation device. If the high-pressure foam fluid does not rupture during energy storage, it is in the foam phase. If it ruptures completely, it separates into gas and liquid phases. If only partially ruptures, it separates into an upper gas phase, a middle foam phase, and a lower liquid phase. Regardless of the downhole situation, as long as the wellhead or a wellbore near the wellhead detects the gas or liquid phase in real time, the respective equipment will be driven to generate electricity. If it is in the foam phase, gas and liquid separation must be performed first.

[0013] Preferably, in step S3, it is first monitored whether there is a demand for power generation. If it is detected that there is a demand for power generation, the control valve on the reverse flow pipe connecting the wellbore corresponding to the formation fracture to the ground is opened, so that the high-pressure fluid in the formation fracture is discharged back to the ground through the reverse flow pipe and drives the corresponding power generation equipment to generate electricity; otherwise, the wellhead is blocked.

[0014] The present invention utilizes high-pressure fluid to be discharged back to the ground to drive power generation equipment to generate electricity, thereby converting the elastic deformation energy of rocks stored in the stratum and the compression energy of gas in the foam into electrical energy again.

[0015] Preferably, the liquid power generation equipment includes but is not limited to a water turbine, a turbine, etc. The gas power generation equipment includes but is not limited to a gas turbine, an expander, etc.

[0016] Preferably, the target formation fracture selected in step S1 includes original formation fractures and / or at least one formation fracture created by hydraulic fracturing of the formation.

[0017] As a mature technology in the oil and gas sector, hydraulic fracturing has been widely used, making related construction equipment readily available and cost-effective. In this technical solution, hydraulic fracturing creates at least one formation fracture and / or opens at least one existing formation fracture to a depth greater than 1,000 meters. In some embodiments, the fracturing fluid contains plugging substances that can physically or chemically seal rock voids and / or microcracks surrounding the formation fractures, reducing the permeability of the rock surrounding the formation fractures and preventing subsequent loss of the energy storage fluid.

[0018] Preferably, in step S2, electric energy is used to drive an injection device to inject high-pressure foam fluid into a target wellbore, and then the high-pressure foam fluid is injected into the target formation fracture through the wellbore until the pressure in the target formation fracture is greater than the closing pressure of the target formation fracture and less than the expansion pressure of the target formation fracture, at which time injection is stopped. If the formation fracture pressure is not reached, injection of high-pressure foam fluid is continued. If it is reached, power is deactivated to the injection device, causing it to stop injecting high-pressure foam fluid into the target wellbore, thereby stopping injection of high-pressure foam fluid into the formation fracture; this can increase the width of the formation fracture while preventing the formation fracture from expanding.

[0019] Preferably, the target formation fracture selected in step S1 is a vertical fracture; during the selection process, whether the formation fracture is a vertical fracture is determined by formation stress data or the depth of the formation fracture.

[0020] In this technical solution, both vertical and horizontal formation fractures can be used for energy storage when the energy storage medium is a high-pressure single-phase fluid (such as a single-phase liquid or gas). However, when the energy storage medium is a high-pressure foam fluid, vertical formation fractures are preferred. This is because when high-pressure foam fluid is stored in formation fractures, a portion of the foam continuously transforms into gas. In horizontal formation fractures, the foam collapses, forming a gas-liquid-bubble mixture within the fractures. When this mixture is discharged, multiphase flow (such as slug flow) occurs in the horizontal fractures and wellbore, significantly increasing frictional losses in the fractures and wellbore, and complicating surface separation of the gas-liquid fluid. In vertical formation fractures, however, the gaseous fluid formed by the foam collapse accumulates above the wellbore and vertical formation fractures due to the density difference, automatically separating from the foam fluid. Therefore, no multiphase flow in the fractures or wellbore occurs during discharge, greatly simplifying surface separation of the gas-liquid fluid. Therefore, vertical formation fractures are used as the primary energy storage medium.

[0021] Fractures created by hydraulic fracturing can be categorized as horizontal and vertical. Horizontal fractures occur when the minimum principal stress in the formation is vertical, while vertical fractures occur when the minimum principal stress in the formation is horizontal. Generally, within 500 meters of formation depth, hydraulic fracturing creates mostly horizontal fractures; at depths exceeding 1000 meters, hydraulic fracturing creates mostly vertical fractures. Therefore, the formation or fracture depth can be used to directly determine whether a fracture is vertical.

[0022] Well logging data (such as density logging) can be used to calculate vertical stress in the formation. The minimum principal stress / fracture closure stress can be determined using a pressure drop curve after hydraulic fracturing, a small-scale fracturing test, or a rapid injection flowback test. When the vertical stress is greater than the fracture closure stress, the formation fractures created by hydraulic fracturing are vertical. When the vertical stress is equal to the fracture closure stress, the formation fractures created by hydraulic fracturing are horizontal. Therefore, formation in-situ stress data can be used to directly determine whether a formation fracture is vertical.

[0023] Preferably, in step S2, the foam fluid is first prepared at room temperature and pressure, and then pressurized by a pressurizing device to form a high-pressure foam fluid and injected into the wellbore.

[0024] The advantage of this method is that the heat generated by the gas in the foam during the compression process is absorbed by water. The specific heat of water is much higher than that of gas, the temperature rise is limited, and there is no need to customize high-temperature resistant equipment or heat absorption system.

[0025] Injection of high-pressure foam fluid into the target wellbore is accomplished using electrically driven injection equipment, including but not limited to centrifugal, plunger, and screw pumps. The target wellbore can be a new energy storage wellbore or an abandoned wellbore. The wellbore can be vertical or horizontal.

[0026] Preferably, the foam fluid configured at normal temperature and pressure includes at least one of air foam, nitrogen foam and carbon dioxide foam; The specific gravity of the foam fluid after preparation at normal temperature and pressure is not higher than 0.8.

[0027] At room temperature and pressure, foam can be generated by adding various foaming agents and foam stabilizers to a water-based solution and mixing it with gas. Preferably, the foam's specific gravity is no higher than 0.8 (relative to water) to reduce its density and increase its gas storage capacity.

[0028] Preferably, in step S2, the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture is calculated based on the injection rate of the high-pressure foam fluid and the depth of the target formation fracture; then, suitable foaming agents and foam stabilizers are selected according to the type of foam, so that the life time T2 of the high-pressure foam fluid is equal to or greater than the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture, thereby ensuring that the high-pressure foam does not completely burst between the time of configuration and the time of transporting into the target formation fracture.

[0029] How long the foam lasts depends on many factors, such as the type of foam, the type of foaming agent and stabilizer, and the temperature and pressure.

[0030] Among them, the air foam uses sodium lauryl sulfate or sodium tetradecene sulfonate as a foaming agent, hydroxypropyl guar gum or partially hydrolyzed polyacrylamide as a stabilizer, and can survive for 1-2 hours under the conditions of 20-80°C and 1-15MPa; the carbon dioxide foam uses fluorocarbon surfactants or betaines as foaming agents, hydrophobically modified cellulose or nano-silica as stabilizers, and can survive for 2-8 hours under the conditions of 30-120°C and 1-20MPa; the nitrogen foam uses sodium tetradecene sulfonate as a foaming agent, and a viscoelastic surfactant as a stabilizer, and can survive for 6-18 hours under the conditions of 10-150°C and 5-35MPa.

[0031] Therefore, to prevent the injected high-pressure foam from completely bursting before reaching the formation fractures, causing severe wellbore multiphase flow, increasing wellbore flow resistance, or damaging injection equipment, the high-pressure foam fluid is configured to not completely burst before being delivered into the formation fractures. The specific method includes the following steps: calculating the time T1 required for the high-pressure foam fluid to be delivered from the surface to the target formation fractures based on the high-pressure foam fluid injection rate and the formation fracture depth; and selecting appropriate foaming agents and foam stabilizers based on the type of foam, so that the high-pressure foam fluid lifespan T2 is equal to or greater than T1, the time it takes for the high-pressure foam fluid to be delivered from the surface to the target formation fractures.

[0032] When the life time T2 of the high-pressure foam fluid is equal to or greater than the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture, and is less than the energy storage time T3, the target formation fracture selected in step S1 is a vertical fracture; during the selection process, whether the formation fracture is a vertical fracture is determined based on the formation stress data or the depth of the formation fracture; Alternatively, when the life time T2 of the high-pressure foam fluid is equal to or greater than the energy storage time T3, the target formation fracture selected in step S1 is a horizontal fracture; during the selection process, whether the formation fracture is a horizontal fracture is determined by formation stress data or the depth of the formation fracture.

[0033] Furthermore, when the stable duration of the foam in the formation fracture (i.e., the lifespan of the high-pressure foam fluid) T2 is greater than the energy storage time T3, the high-pressure fluid released and discharged remains in a foamy state. When the stable duration of the foam in the formation fracture (i.e., the lifespan of the high-pressure foam fluid) T2 is less than the energy storage time T3, the foam decomposes into gas and liquid phases within the formation fracture before energy release. Due to density differences, the gas phase is stored as a high-pressure gas fluid in the upper portion of the vertical formation fracture and in the wellbore, while the liquid phase is stored as a high-pressure liquid fluid in the lower portion of the formation fracture.

[0034] Preferably, in step S3, the separation device performs gas-liquid separation by changing the temperature or / and adding a defoaming agent or / and centrifugal force; At the end of energy release, the volume of the high-pressure foam fluid remaining in the target formation fracture is greater than or equal to a preset minimum volume threshold.

[0035] To reduce the frictional resistance of fluid flow in the fractures, at the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fractures must be greater than or equal to a preset volume threshold, thereby ensuring that the fracture width during the energy storage and release cycles is greater than or equal to a preset width threshold (the smaller the fracture width, the greater the frictional resistance). Both the preset volume threshold and the preset width threshold can be calculated using physical models (such as hydraulic fracturing models, wellbore-fracture flow models). For example, to ensure that the impact of frictional resistance loss from fluid flow in the fracture on the energy storage cycle efficiency is less than 10%, a physical model (such as a hydraulic fracturing model or a wellbore-fracture flow model) can be used to calculate, using known information (such as fracture height, fracture length, rock Young's modulus, rock Poisson's ratio, rock fracture properties, and fluid displacement rate), the minimum fracture width must be no less than 0.3 cm (i.e., the preset width threshold). This corresponds to a minimum volume of high-pressure foam fluid in the formation fracture of no less than 1000 cubic meters, and a high-pressure fluid volume for backflow of 5000 cubic meters. Therefore, 1000 cubic meters is used as the preset volume threshold. At the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fractures must be no less than 1000 cubic meters. For another example, to minimize the impact of frictional resistance losses caused by fluid flow in the fractures on the energy storage cycle efficiency by less than 5%, a physical model, utilizing known information (such as fracture height, fracture length, rock Young's modulus, rock Poisson's ratio, rock fracture dynamics, and fluid displacement), calculates that the minimum fracture width must be no less than 0.5 cm (the preset width threshold). This corresponds to a minimum volume of high-pressure foam fluid within the fracture of no less than 1500 cubic meters. The volume of high-pressure fluid used for backflow is 4500 cubic meters. Therefore, 1500 cubic meters is used as the preset volume threshold. At the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fractures must be no less than 1500 cubic meters. Generally, these two thresholds can be set based on the desired energy storage cycle efficiency. In special circumstances (such as those requiring emergency power generation or energy storage), the thresholds can be adjusted upward or downward based on actual conditions. At the end of energy release, the volume of high-pressure foam fluid remaining in the formation fracture is greater than or equal to the preset minimum volume threshold, which is equivalent to the pressure in the formation fracture being greater than or equal to the preset minimum pressure at the end of energy release, and the minimum pressure being greater than the closing stress of the formation fracture (i.e., the fracture is still in an open state).

[0036] Preferably, during the energy release process of step S3, the high-pressure liquid fluid generates electricity through a preset liquid power generation device and the liquid fluid is recovered at the same time; when the high-pressure gas fluid is not a gas, the gas fluid is recovered at the same time after generating electricity through a preset gas power generation device; the recovered liquid fluid and gas fluid can both be used for the configuration of the foam fluid in step S2.

[0037] The second aspect of the present invention is to provide a system for storing and releasing energy using foam, comprising: a foam injection device, a backflow pipe, a monitoring device, a blocking device, a gas power generation device, and a liquid power generation device. The foam injection device includes a foam generating device, a foam storage device and a pressurized injection pump; the foam generating device, the foam storage device and the pressurized injection pump are connected in sequence, and the pressurized injection pump is connected to the wellbore through an injection pipe to inject high-pressure foam fluid into the wellbore; The wellbore is connected to the formation fracture; The monitoring device is provided at the wellhead and is used to monitor and determine the parameters of the fluid in the wellhead or wellbore, thereby determining the state of the fluid discharged from the wellhead; The reverse discharge pipeline is connected to a gas power generation device and a liquid power generation device; The plugging device is used to close the reverse flow pipeline and plug the wellhead.

[0038] Preferably, the foam generating device includes at least one of a Venturi foam generator, a gas-liquid mixer, a nozzle foam generator, a mechanical stirring foam generator, and a rotating disk foam generator.

[0039] In the present technical solution, the foam generating device includes but is not limited to at least one of the following devices: a Venturi-type foam generator (utilizing the acceleration effect of the fluid passing through the Venturi tube to form a negative pressure at the narrowest part of the pipe to inhale gas, which is mixed with the foaming liquid to form foam), a gas-liquid mixer (the gas and foaming liquid are forcibly mixed through a static mixer or a stirrer to form foam in the pipe), a nozzle-type foam generator (the foaming liquid is sprayed at high speed by a nozzle, and gas is introduced at the same time, so that it is quickly mixed into foam during the spraying process), a mechanical stirring foam generator (the foaming liquid is mechanically stirred by a stirrer, and gas is continuously injected to form foam in the stirring chamber), and a rotating disk-type foam generator (the foaming liquid is thrown out through a rotating disk, and gas is injected at the same time to form uniform foam under the action of centrifugal force).

[0040] Preferably, the reverse discharge pipeline is further connected to a separation device, and the gas power generation device and the liquid power generation device are respectively connected via the separation device.

[0041] Preferably, the separation device includes a body for accommodating high-pressure foam fluid, a foam fluid inlet is provided on one side of the body, and a high-pressure gas fluid outlet and a high-pressure liquid fluid outlet are provided on the other side; a heating module is provided at the bottom of the body and / or a defoaming agent inlet is provided at the top of the body.

[0042] The separation device can separate gas and liquid by changing the temperature and / or adding a defoaming agent. However, the defoaming agent has significant limitations due to the need to consider recycling and its impact on the re-foaming of the recycled liquid. Therefore, in this technical solution, defoaming by changing the temperature is preferred.

[0043] Preferably, the system further comprises a fracturing device for pumping fracturing fluid into a wellbore through a wellbore leading to the energy storage geothermal layer so as to generate formation fractures in the energy storage geothermal layer.

[0044] Preferably, the reverse discharge pipeline is further connected to a liquid storage container, the liquid storage container is connected to the gas power generation device and the liquid power generation device, and the liquid storage container is used to store the reversed high-pressure fluid.

[0045] Compared with the existing technology, the present invention has the following beneficial technical effects: using the foam energy storage and release method and system to inject high-pressure foam fluid into the target formation fractures, the target formation fracture pressure is increased, and the electrical energy is converted into the elastic deformation energy of the formation rock and the compression energy of the gas in the foam for storage; then the high-pressure foam fluid discharged from the wellhead during the closing process of at least one of the target formation fractures is used to drive the power generation equipment to generate electricity to release energy. This method can greatly increase the effective energy storage density of the formation fractures and reduce the energy consumed by the gravitational potential energy during the fluid backflow process. At the same time, the system has a simple structure, which greatly reduces the investment cost and maintenance cost of ground equipment, and is of great significance for wind power generation or solar power generation grid-connected peak regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the embodiments or the description of the prior art. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the various elements or parts are not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work.

[0047] Figure 1 This is a flow chart of the method for storing and releasing energy using foam according to the present invention; Figure 2A A flow chart of a conventional method of injecting foam into formation fractures; Figure 2B This is a flow chart of a method for injecting foam into formation fractures using the foam energy storage and release method of the present invention; Figure 3 This is a structural diagram of a system utilizing foam energy storage and release without a separation device in system embodiment 1 of the present invention; Figure 4 This is a structural diagram of a system utilizing foam energy storage and release with a separation device in system embodiment 2 of the present invention; Figure 5 This is a structural diagram of a foam separation device that utilizes a heating device for separation in system embodiment 2 of the present invention; Figure 6 This is a structural diagram of a foam separation device using a defoaming agent for separation in system embodiment 2 of the present invention; Figure 7This is a structural diagram of a system utilizing foam energy storage and release with a liquid reservoir in system embodiment 3 of the present invention; Figure numerals: 1-foam inlet; 2-high-pressure gas fluid outlet; 3-high-pressure liquid fluid outlet; 4-foam; 5-high-pressure gas fluid; 6-high-pressure liquid fluid; 7-heating device; 8-defoaming agent inlet. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] As used herein, "and / or" includes any and all combinations of one or more of the listed items. As used herein, "at least one" means one or more, i.e., it includes one, two, three, four, etc. In this specification, certain embodiments may be disclosed in a format that is within a certain range. It should be understood that this description of "being within a certain range" is merely for convenience and brevity and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered to have specifically disclosed all possible sub-ranges and independent numerical values ​​within this range. For example, the description of a range of 1-6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. Regardless of the breadth of the range, the above rules apply.

[0050] Definition of term: "fluid" in this article can be but not limited to liquid, emulsion, slurry and solid particle flow with flow characteristics similar to liquid flow; The "gas fluid" herein can be, but is not limited to, air, nitrogen, carbon dioxide, or gases including different components.

[0051] As used herein, a "formation" is a porous and permeable rock formation (e.g., shale formation, sandstone formation, carbonate formation, hot dry rock formation, etc.) underground that can serve as a reservoir for fluids, typically water, hydrocarbons, or gases.

[0052] "Hydraulic fracturing," "fracture," or "fracturing" in this article refers to the formation and propagation of cracks in formation rocks under the action of external forces (such as high-pressure fluids). "Formation fractures" or "fractures" in this article refer to open rock cracks created by hydraulic fracturing or to pre-existing natural fractures or faults in the formation. The terms "formation fractures" and "fractures" are used interchangeably. "Fractures" can refer to a single fracture, multiple adjacent fractures at the same location, or a fracture cluster.

[0053] As used herein, a "wellbore" refers to a hole drilled or inserted into a formation. Typically, a wellbore is cylindrical, and therefore may have a circular cross-section. However, a wellbore may have any other cross-section. A wellbore may be open-hole or cased, with casing cemented to the inner wall. A wellbore may be vertical, horizontal, or inclined. The term "fracture closure pressure" used in this article refers to the minimum pressure at which a fracture opens. It is equal to the in-situ stress perpendicular to the fracture plane and is typically the minimum principal stress of the formation. For horizontal fractures, the fracture closure pressure is typically equal to the vertical principal stress of the formation. For vertical fractures, the fracture closure pressure is typically equal to the minimum horizontal principal stress of the formation.

[0054] The term "fracture pressure" or "in-fracture pressure" used in this article refers to the average pressure within formation fractures. Fracture pressure can be measured by monitoring wellhead pressure (fracture pressure = wellhead pressure + hydrostatic pressure - frictional resistance) or wellbore pressure. Using a wellbore flow model, the dynamic relationship between wellhead pressure and fracture pressure can be calculated under varying injection rates and fluid density / temperature conditions. The "fracture propagation pressure" in this article refers to the pressure at which a formation fracture begins to expand in length or height, and is typically greater than the "fracture closure pressure." Fracture propagation pressure can be determined using empirical formulas, rock mechanics model equations, well logging data, numerical modeling, and other methods. It can also be obtained through field measurements (such as overflow tests, formation integrity tests, small-scale fracturing tests, and step-by-step pressure tests).

[0055] "High-pressure fluid" in this context includes pressurized fluids injected into a wellbore using injection equipment, as well as fluids discharged from the wellhead or near the wellbore. Such fluids may contain liquid, gas, or foam phases. The foam phase may decay into a gas and / or liquid phase over time. Accordingly, if the injected fluid is a foam phase, it is referred to as "high-pressure foam fluid."

[0056] Example: Figure 1 As shown, the method of utilizing foam to store and release energy specifically comprises the following steps: S1: Select at least one target formation fracture; preferably, the target formation fracture is connected to only one wellbore through the formation.

[0057] The target formation fracture selected in step S1 includes original formation fractures and / or at least one formation fracture created by hydraulic fracturing of the formation. Preferably, the target formation fracture is connected to only one wellbore through the formation, that is, the target formation fracture is not connected to multiple wellbores in the underground space, so that each target formation fracture and the wellbore it is connected to form an independent energy storage system that is not affected by other wellbores. In other words, when there are multiple wellbores, the wellbores are not connected to each other, but each wellbore is connected to the corresponding fracture.

[0058] In some embodiments, the fracturing fluid contains plugging substances that can physically or chemically seal rock voids and / or microcracks around formation fractures, reduce rock permeability around formation fractures, and prevent subsequent energy storage fluid loss.

[0059] While both vertical and horizontal formation fractures can be used for energy storage when the energy storage medium is a high-pressure single-phase fluid (such as a single-phase liquid or gas), the morphology of the formation fractures can affect the energy storage efficiency when the energy storage medium is a high-pressure foam fluid. This is because when high-pressure foam fluid is stored in formation fractures, a portion of the foam continuously decays into gas and liquid phases.

[0060] When the stable duration of high-pressure foam fluid in formation fractures (i.e., its lifespan) T2 is equal to or greater than the energy storage time T3, the high-pressure foam fluid remains in a foamy state within the formation fractures (the effect of minimal foam decay can be ignored). Both vertical and horizontal fractures can be used for energy storage, but horizontal fractures are preferred because they are shallower and less expensive to stimulate. Furthermore, horizontal fractures are typically circular fractures within the same reservoir, making their geometry easier to control. However, the geometry of vertical fractures is significantly affected by formation stress and mechanical conditions.

[0061] When the stable duration of high-pressure foam fluid in formation fractures (i.e., its lifespan), T2, is less than the energy storage time, the foam collapses, forming a gas-liquid-bubble mixture within the fractures. When this mixture is discharged, multiphase flow (such as slugging) occurs in horizontal fractures and the wellbore, significantly increasing frictional losses within the fractures and wellbore, and complicating surface separation of the gas-liquid fluid. In vertical fractures, however, the gaseous fluid formed by the foam collapse accumulates above the wellbore and vertical fractures due to density differences, automatically separating from the foam fluid. Therefore, multiphase flow in the fractures or wellbore is avoided during discharge, significantly simplifying surface separation of the gas-liquid fluid. Therefore, when the high-pressure foam fluid persists in formation fractures for less than the energy storage time, vertical fractures are used as the primary energy storage medium.

[0062] Specifically, when the life time T2 of the high-pressure foam fluid is equal to or greater than the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture, and is less than the energy storage time T3, the target formation fracture selected in step S1 is a vertical fracture; during the selection process, whether the formation fracture is a vertical fracture is determined based on the formation stress data or the depth of the formation fracture; Alternatively, when the life time T2 of the high-pressure foam fluid is equal to or greater than the energy storage time T3, the target formation fracture selected in step S1 is a horizontal fracture; during the selection process, whether the formation fracture is a horizontal fracture is determined by formation stress data or the depth of the formation fracture.

[0063] Fractures created by hydraulic fracturing can be categorized as horizontal and vertical. Horizontal fractures occur when the minimum principal stress in the formation is vertical, while vertical fractures occur when the minimum principal stress in the formation is horizontal. Generally, within 500 meters of formation depth, hydraulic fracturing creates mostly horizontal fractures; at depths exceeding 1000 meters, hydraulic fracturing creates mostly vertical fractures. Therefore, the formation or fracture depth can be used to directly determine whether a fracture is vertical or horizontal.

[0064] Well logging data (such as density logging) can be used to calculate vertical stress in the formation. The minimum principal stress / fracture closure stress can be determined using a pressure drop curve after hydraulic fracturing, a small-scale fracturing test, or a rapid injection flowback test. When the vertical stress is greater than the fracture closure stress, the formation fractures created by hydraulic fracturing are vertical. When the vertical stress is equal to the fracture closure stress, the formation fractures created by hydraulic fracturing are horizontal. Therefore, formation in-situ stress data can be used to directly determine whether a formation fracture is vertical or horizontal.

[0065] In some embodiments, when hydraulic fracturing is used to generate formation fractures in step S11, the injected fracturing fluid is pumped into the wellbore via surface facilities, and the fracturing fluid is then pumped into the vertical or horizontal wellbore via a fracturing device. Once the bottomhole pressure of the vertical or horizontal wellbore reaches the fracture pressure of the underground rock formation (i.e., the energy storage formation) (i.e., the bottomhole pressure is greater than or equal to the fracture pressure), the formation fractures in the vertical wellbore will initiate from around the vertical wellbore and propagate into the underground rock formation until pumping is stopped (i.e., the hydraulic fracturing operation is stopped). Correspondingly, the formation fractures in the horizontal wellbore will initiate from around the horizontal wellbore and propagate into the underground rock formation until pumping is stopped. The formation fractures may form a planar geometry and propagate in a direction perpendicular to the minimum principal stress of the shale formation. However, under certain geological conditions, some formation fractures may interact with pre-existing natural fractures to form complex fracture geometries (see the applicant's prior application CN114016988 A).

[0066] In practical applications, the expansion degree of formation fractures can be determined according to different energy storage requirements and the mechanical properties of the energy storage formation. For example, if more energy needs to be stored, longer formation fractures need to be designed, and more geothermal energy can be obtained at the same time. If relatively less energy needs to be stored, shorter formation fractures need to be designed, and the geothermal energy obtained is correspondingly less. Therefore, the design parameters of the formation fractures, such as the expansion radius (or expansion length), can be set in advance according to actual needs. When it is determined that the expansion radius of the formation fractures reaches the design requirements, the pumping of fracturing fluid is stopped (that is, the hydraulic fracturing construction is stopped), so that the formation fractures gradually stop expanding.

[0067] During hydraulic fracturing, a determination is made as to whether the expansion radius of the formation fracture is equal to or greater than a target radius. Specifically, the three-dimensional shape of the formation fracture is calculated based on a pre-established hydraulic fracturing model, rock mechanical properties, and a first construction parameter, and the expansion radius of the formation fracture is determined based on the three-dimensional shape. In some embodiments, the hydraulic fracturing model may employ a two-dimensional PKN model, a KGD model, a RADIAL model, a pseudo-3D model, or a full 3D model. The first construction parameter is the construction parameter of the surface facilities (i.e., the injection equipment in the hydraulic fracturing operation apparatus), including the injection rate, total injection volume, and viscosity of the fracturing fluid. If a formation fracture is detected with an expansion radius equal to or greater than the target radius, hydraulic fracturing is terminated.

[0068] Of course, in other embodiments, when to stop hydraulic fracturing construction can be determined by the staff based on relevant work experience. For example, the staff can determine or calculate the time to stop hydraulic fracturing construction based on work experience, combined with the injection rate, total injection volume and viscosity of the fracturing fluid.

[0069] In some embodiments, the preset target radius is set by professional technicians based on the mechanical properties of the energy storage formation, ensuring that the formation cracks have a certain storage capacity while avoiding the expansion radius of the formation cracks being too large to cause damage to the energy storage formation.

[0070] In some embodiments, multiple formation fractures are created during hydraulic fracturing. To prevent excessive expansion radius of the formation fractures, which could damage the energy storage formation, hydraulic fracturing is preferably stopped when a formation fracture is detected with an expansion radius equal to or greater than a preset target radius. Alternatively, hydraulic fracturing may be stopped when the average expansion radius of all formation fractures is determined to be equal to or greater than the preset target radius.

[0071] It is understandable that when hydraulic fracturing construction is stopped, the formation fractures will not stop expanding immediately. Only when the fluid pressure in the formation fractures tends to be balanced with the fracture pressure, that is, when the fluid pressure is less than the fracture pressure, will the formation fractures stop expanding. Therefore, in order to avoid the expansion radius of the formation fractures being too large, preferably, in some embodiments, hydraulic fracturing construction is stopped when the expansion radius of the formation fractures is approximately equal to (or close to) the target radius (for example, expansion radius = target radius × 0.90-0.95).

[0072] In order to reduce the rate of fracturing fluid in the formation fractures to the surrounding rocks, so that the formation fractures in the energy storage formation have the ability to store fracturing fluid or high-pressure fluid for a long time, in some embodiments, a fluid loss preventer is added to the fracturing fluid in the hydraulic fracturing construction in this step.

[0073] In some embodiments, the fluid loss agent may include: at least one high molecular weight polymer, and / or at least one resin, and / or at least one gel and other additives. After the fluid loss agent is injected into the formation fracture, it covers the surface of the formation fracture to form a cap layer with an extremely low leakage rate. In addition, the fluid loss agent can also be particles with the effect of plugging the pores of the rock matrix of the energy storage formation, such as micro-nano materials. During the fluid loss process, the particles are filled into the rock matrix pores around the formation fracture, reducing the permeability of the energy storage formation and achieving a fluid loss prevention effect.

[0074] In some embodiments, the fluid loss agent may include: at least one silicate, and / or sulfate, and / or phosphate, and / or oxalate, which reacts with formation mineral cations to generate precipitates to plug the pores of the formation rock matrix.

[0075] S2: Injecting high-pressure foam fluid into at least one of the target formation fractures to increase the pressure of at least one of the target formation fractures and increase the fracture width; thereby converting electrical energy into elastic deformation energy of the formation rock and compression energy of the gas in the foam for storage.

[0076] That is, the electrical energy is converted into elastic potential energy generated by the deformation of the formation rock and stored; and the potential energy of the compressed air in the target formation crack is stored due to the pressure increase in the space caused by the gas in the foam.

[0077] In practical applications, the degree of expansion of formation fractures can be determined according to different energy storage requirements and the mechanical properties of the energy storage formation. For example, if more energy needs to be stored, longer formation fractures need to be designed; if relatively less energy needs to be stored, shorter formation fractures need to be designed. Therefore, the parameters of the target formation fractures, such as the target length threshold, the target height threshold, and the target fracture number threshold, can be set in advance according to actual needs. When it is determined that the identified formation fractures have reached the desired target threshold, high-pressure foam fluid is directly injected into them to increase their width to the target width for energy storage. Of course, if the identified formation fractures do not reach the desired target threshold, high-pressure foam fluid can be injected into them for transformation, i.e., to expand them in height or length until they meet the corresponding target threshold.

[0078] In step S2, electric energy is used to drive the injection device to inject high-pressure foam fluid into the target wellbore, and then the high-pressure foam fluid is injected into the target formation fracture through the wellbore until the pressure of the target formation fracture is greater than the closing pressure of the target formation fracture and less than the expansion pressure of the target formation fracture, and then the injection is stopped.

[0079] In step S211, it is determined whether the pressure of the target formation fracture is greater than the closing pressure of the target formation fracture and less than the expansion pressure of the target formation fracture. If not, the injection of high-pressure foam fluid continues. If it reaches the closing pressure, the power supply to the injection equipment is stopped, that is, step S212 stops the injection of high-pressure foam fluid into the target wellbore, thereby stopping the injection of high-pressure foam fluid into the formation fracture; in this way, the width of the formation fracture is increased while the formation fracture does not expand; the injection equipment includes but is not limited to a centrifugal injection pump, a plunger injection pump, and a screw injection pump.

[0080] Traditional foam-based hydraulic fracturing of oil and gas reservoirs typically requires liquid nitrogen, liquid carbon dioxide, or supercritical carbon dioxide as the gas source. These require extremely low temperatures or high pressures to be stored on-site. After being pressurized by a booster, they are mixed with a high-pressure water-based foaming fluid injected into the wellbore to produce foam. This method places high demands on surface equipment and is expensive to store, making it unsuitable for energy storage (see Figure 2A ).

[0081] In some embodiments, in step S2, the foam fluid is first prepared at room temperature and pressure, then pressurized by a pressurizing device to form a high-pressure foam fluid and injected into the wellbore. The advantage of this method is that the heat generated by the gas in the foam during compression is absorbed by the water. The specific heat of water is much higher than that of gas, so the temperature rise is limited, and no customized high-temperature resistant equipment or heat absorption system is required (see Figure 2B ).

[0082] The foam fluid prepared at room temperature and pressure includes at least one of air foam, nitrogen foam, and carbon dioxide foam; the specific gravity of the foam fluid after preparation at room temperature and pressure is no higher than 0.8. Foam can be generated at room temperature and pressure by adding various foaming agents and foam stabilizers to a water-based solution and mixing it with gas. Therefore, to better reduce foam density and increase gas storage capacity, the foam is prepared with a specific gravity no higher than 0.8 (relative to water).

[0083] In some embodiments, injection of high-pressure foam fluid into the target wellbore is accomplished using electrically driven injection equipment, including but not limited to centrifugal injection pumps, plunger injection pumps, and screw injection pumps. The target wellbore can be a new energy storage wellbore or an abandoned wellbore. The wellbore can be vertical or horizontal.

[0084] In step S2, the time T1 required for the high-pressure foam fluid to be transported from the ground to the target formation fracture is calculated based on the injection rate of the high-pressure foam fluid and the depth of the target formation fracture. Then, suitable foaming agents and foam stabilizers are selected according to the type of foam, so that the life span T2 of the high-pressure foam fluid is equal to or greater than the time T1 required for the high-pressure foam fluid to be transported from the ground to the target formation fracture, thereby ensuring that the high-pressure foam does not completely rupture between the time of configuration and the time of transporting into the target formation fracture.

[0085] How long the foam lasts depends on many factors, such as the type of foam, the type of foaming agent and stabilizer, and the temperature and pressure.

[0086] In some embodiments, the air foam in step S2 uses sodium lauryl sulfate or sodium tetradecene sulfonate as a foaming agent, and hydroxypropyl guar gum or partially hydrolyzed polyacrylamide as a stabilizer, and can survive for 1-2 hours at 20-80°C and 1-15 MPa; the carbon dioxide foam uses fluorocarbon surfactants or betaines as a foaming agent, and hydrophobically modified cellulose or nano-silica as a stabilizer, and can survive for 2-8 hours at 30-120°C and 1-20 MPa; the nitrogen foam uses sodium tetradecene sulfonate as a foaming agent and a viscoelastic surfactant as a stabilizer, and can survive for 6-18 hours at 10-150°C and 5-35 MPa.

[0087] Therefore, to prevent the injected high-pressure foam from completely bursting before reaching the formation fractures, causing severe wellbore multiphase flow, increasing wellbore flow resistance, or damaging injection equipment, the high-pressure foam fluid is configured to not completely burst before being delivered into the formation fractures. The specific method includes the following steps: calculating the time T1 required for the high-pressure foam fluid to be delivered from the surface to the target formation fractures based on the high-pressure foam fluid injection rate and the formation fracture depth; and selecting appropriate foaming agents and foam stabilizers based on the type of foam, so that the high-pressure foam fluid lifespan T2 is equal to or greater than T1, the time it takes for the high-pressure foam fluid to be delivered from the surface to the target formation fractures.

[0088] When the stable duration of the foam in the formation fracture (i.e., the lifespan of the high-pressure foam fluid) T2 is greater than the energy storage time T3, the high-pressure fluid released and discharged remains in a foamy state. When the stable duration of the foam in the formation fracture (i.e., the lifespan of the high-pressure foam fluid) T2 is less than the energy storage time T3, the foam has already decomposed into gas and liquid phases in the formation fracture before energy release. Due to density differences, the gas phase is stored as a high-pressure gas fluid in the upper part of the vertical formation fracture and in the wellbore, while the liquid phase is stored as a high-pressure liquid fluid in the lower part of the formation fracture.

[0089] S3: utilizing the high-pressure fluid discharged from the wellhead during the closing process of at least one of the target formation fractures, and driving the corresponding power generation equipment to generate electricity according to the state of the high-pressure fluid to release energy.

[0090] That is, high-pressure fluid is discharged back to the ground to drive the power generation equipment to generate electricity, thereby converting the elastic deformation energy of the rock stored in the formation and the compression energy of the gas in the foam into electrical energy again.

[0091] In step S3, step S31 in step S3 first monitors whether there is a demand for power generation. If it is detected that there is a demand for power generation, step S32 is performed to open the control valve on the backflow pipe connecting the wellbore corresponding to the formation fracture to the ground, so that the high-pressure foam fluid in the formation fracture is backflowed to the ground through the backflow pipe and drives the corresponding power generation equipment to generate electricity; otherwise, the wellhead is blocked.

[0092] In some embodiments, an injection pipe (the valve is in a closed state) is passed between the foam generating device and the wellbore corresponding to the formation fracture. Therefore, when the demand for power generation is detected, the control valve corresponding to the reverse discharge pipe is opened to allow the reverse discharge pipe to circulate, so that the high-pressure foam fluid in the formation fracture can be discharged back to the ground through the reverse discharge pipe under the action of rock compression, and at the same time drive the power generation equipment to generate electricity.

[0093] In some embodiments, both the injection pipeline and the backflow pipeline are provided with control valves for controlling the circulation and closure of the surface pipeline, and the control valve corresponding to the injection pipeline is in a closed state after the injection of high-pressure foam fluid into the formation fracture is stopped and before the need for power generation is detected. When the need for power generation is detected (for example, the corresponding control system, or the first power generation equipment, or the corresponding staff will receive a power supply request from the outside, such as the power grid or other control system), the control system connected to the control valve, or opens the control valve corresponding to the backflow pipeline (of course, it can also be opened manually by the staff), so that the wellbore and the liquid reservoir or liquid tank are connected, and then under the action of rock compression, the high-pressure foam fluid in the formation fracture is backflowed into the liquid reservoir or liquid tank, and drives the power generation equipment to generate electricity; of course, if no power supply request is received, the control valve of the backflow pipeline between the wellbore and the liquid reservoir or liquid tank will always remain closed, that is, in a normally closed state.

[0094] In step S3, after detecting the need for power generation, the state of the high-pressure fluid discharged is first determined during the closing process, and the state of the high-pressure fluid discharged from the wellhead is determined by monitoring the fluid pressure in the wellhead or wellbore, and / or the fluid density, and / or the fluid dielectric constant, and / or the sound wave propagation speed in the fluid; the high-pressure fluid discharged is classified into high-pressure gas fluid, high-pressure liquid fluid and high-pressure foam fluid according to the state of the high-pressure fluid.

[0095] When the reversed high-pressure fluid is in a gaseous state, that is, a high-pressure gas fluid, the reversed high-pressure gas fluid is first utilized to drive the preset gas power generation equipment to generate electricity.

[0096] When the high-pressure gas fluid in the wellbore and the cracks of the target formation is emptied, the remaining high-pressure liquid fluid is discharged back, thereby driving the preset liquid power generation equipment to generate electricity.

[0097] If the high-pressure fluid discharged from the wellhead during the closure process is high-pressure foam fluid, it is first transported to a separation device for gas-liquid separation. The resulting high-pressure liquid and gas fluids are then used to drive their respective pre-set power generation equipment to generate electricity. The pre-set power generation equipment can be connected to a wind or solar power generation grid.

[0098] The state of the high-pressure fluid discharged from the wellhead is determined by monitoring the pressure of the high-pressure fluid in the wellhead or wellbore, and / or the density of the high-pressure fluid, and / or the dielectric constant of the high-pressure fluid, and / or the propagation speed of sound waves in the high-pressure fluid. Accordingly: If the density of the high-pressure fluid is less than a first preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is gas phase, i.e., high-pressure gas fluid; If the density of the high-pressure fluid is greater than a second preset density threshold and less than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is foam, i.e., high-pressure foam fluid; If the density of the high-pressure fluid is greater than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is liquid, i.e., high-pressure liquid fluid; The first preset density threshold is smaller than the second preset density threshold, and the second preset density threshold is smaller than the third preset density threshold.

[0099] Alternatively, if the dielectric constant of the high-pressure fluid is less than a first preset dielectric threshold, it is determined that the state of the high-pressure fluid in the wellhead or wellbore is gas phase, i.e., high-pressure gas fluid; If the dielectric constant of the high-pressure fluid is greater than a second preset dielectric threshold and less than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is foam, i.e., high-pressure foam fluid; If the dielectric constant of the high-pressure fluid is greater than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is liquid, i.e., high-pressure liquid fluid; The first preset dielectric threshold is smaller than the second preset dielectric threshold, and the second preset dielectric threshold is smaller than the third preset dielectric threshold.

[0100] Alternatively, if the propagation speed of the sound wave in the high-pressure fluid is less than a first preset sound speed threshold, it is determined that the state of the high-pressure fluid in the wellhead or wellbore is gas phase, i.e., high-pressure gas fluid; If the propagation speed of sound waves in the high-pressure fluid is greater than a second preset sound speed threshold and less than a third preset sound speed threshold, it is determined that the state of the high-pressure fluid in the wellhead or wellbore is foam, i.e., high-pressure foam fluid; If the acoustic wave propagation speed of the high-pressure fluid is greater than a third preset acoustic speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is liquid, i.e., high-pressure liquid fluid; The first preset sound speed threshold is smaller than the second preset sound speed threshold, and the second preset sound speed threshold is smaller than the third preset sound speed threshold.

[0101] Specifically, in some embodiments, a pressure gauge installed at the wellhead can monitor the wellhead pressure. Wellhead pressure = formation fracture fracturing pressure - wellbore hydrostatic pressure, where formation fracture fracturing pressure is between the fracture closure stress and the fracture expansion pressure. Wellbore hydrostatic pressure = wellbore fluid density * wellbore length * gravitational acceleration constant. Therefore, given the fracture closure stress, fracture expansion pressure, wellbore length, and wellhead pressure, the wellbore hydrostatic pressure and, consequently, the wellbore fluid density can be calculated. When the calculated wellbore fluid density is less than 250 kg / m³, the wellbore can be determined to contain gas. When the calculated wellbore fluid density is greater than 400 kg / m³ and less than 900 kg / m³, the wellbore can be determined to contain foam. When the calculated wellbore fluid density is greater than 1000 kg / m³, the wellbore can be determined to contain liquid.

[0102] In some embodiments, by installing multiple pressure gauges or optical fibers within the wellbore, pressure at different depths can be monitored, thereby obtaining the hydrostatic pressure within the entire wellbore or a portion thereof, and thereby calculating the wellbore fluid density. When the calculated wellbore fluid density is less than 250 kg / m³, the wellbore can be determined to contain gas; when the calculated wellbore fluid density is greater than 400 kg / m³ and less than 900 kg / m³, the wellbore can be determined to contain foam; and when the calculated wellbore fluid density is greater than 1000 kg / m³, the wellbore can be determined to contain liquid.

[0103] In some embodiments, a Coriolis mass flowmeter or gamma-ray densitometer is installed at the wellhead or in the wellbore to directly measure fluid density. When the measured wellbore fluid density is less than 250 kg / m³, the wellbore can be determined to contain gas. When the measured wellbore fluid density is greater than 400 kg / m³ and less than 900 kg / m³, the wellbore can be determined to contain foam. When the measured wellbore fluid density is greater than 1000 kg / m³, the wellbore can be determined to contain liquid.

[0104] In some embodiments, a capacitance sensor is installed at the wellhead or in the wellbore to directly measure the dielectric constant of the wellbore fluid. When the measured dielectric constant of the wellbore fluid is less than 1.5, it can be determined that the wellbore contains gas. When the measured dielectric constant of the wellbore fluid is greater than 1.5 and less than 40, it can be determined that the wellbore contains foam. When the measured dielectric constant of the wellbore fluid is greater than 40, it can be determined that the wellbore contains liquid. In some embodiments, an ultrasonic sensor is installed at the wellhead or within the wellbore to directly measure the wellbore fluid sound velocity. When the measured wellbore fluid sound velocity is less than 500 m / s, the wellbore can be determined to contain gas. When the measured wellbore fluid sound velocity is greater than 500 m / s and less than 1200 m / s, the wellbore can be determined to contain foam. When the measured wellbore fluid sound velocity is greater than 1200 m / s, the wellbore can be determined to contain liquid.

[0105] When the high-pressure fluid discharged from the wellhead is still foam, it is necessary to first transport the high-pressure foam fluid to a separation device for gas-liquid separation. In step S3, the separation device performs gas-liquid separation by changing the temperature and / or by centrifugal force and / or by adding a defoaming agent. Because the foamed fluid cannot generate electricity using existing technology, the foam needs to be separated into high-pressure liquid fluid and high-pressure gas fluid. The high-pressure liquid fluid generates electricity through a preset liquid power generation device, and the high-pressure gas fluid generates electricity through a preset gas power generation device. Liquid power generation equipment includes but is not limited to water turbines, turbines, etc. Gas power generation equipment includes but is not limited to gas turbines, expanders, etc.

[0106] At the end of energy release, the volume of the high-pressure foam fluid remaining in the target formation fracture is greater than or equal to a preset minimum volume threshold.

[0107] In other embodiments, to reduce the frictional resistance of fluid flow in the fracture, at the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fracture is greater than or equal to a preset volume threshold, thereby ensuring that the fracture width of the formation fracture is greater than or equal to a preset width threshold during the energy storage and release cycle (the smaller the fracture width, the greater the frictional resistance). Both the preset volume threshold and the preset width threshold can be calculated using a physical model (such as a hydraulic fracturing model, etc.). For example, to ensure that the impact of frictional resistance loss of fluid flow in the fracture on the energy storage cycle efficiency is less than 10%, a physical model (such as a hydraulic fracturing model or a wellbore-fracture flow model) can be used, utilizing known information (such as fracture height, fracture length, rock Young's modulus, rock Poisson's ratio, rock fracture properties, and fluid displacement) to calculate that the minimum fracture width cannot be less than 0.3 cm (i.e., the preset width threshold). This corresponds to a minimum volume of high-pressure foam fluid in the formation fracture of no less than 1000 cubic meters, and a volume of high-pressure foam fluid used for backflow of 5000 cubic meters. Therefore, 1000 cubic meters is used as the preset volume threshold. At the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fractures must be no less than 1000 cubic meters. For another example, to ensure that the frictional resistance loss of high-pressure foam fluid flowing in the fractures affects the energy storage cycle efficiency by less than 5%, a physical model, using known information (such as fracture height, fracture length, rock Young's modulus, rock Poisson's ratio, rock fracture dynamics, and fluid displacement), calculates that the minimum fracture width must not be less than 0.5 cm (the preset width threshold). This corresponds to a minimum volume of high-pressure foam fluid within the fracture of no less than 1500 cubic meters. The volume of high-pressure foam fluid used for backflow is 4500 cubic meters. Therefore, 1500 cubic meters is used as the preset volume threshold. At the end of the energy release process, the volume of high-pressure foam fluid retained in the formation fractures must be no less than 1500 cubic meters. Generally, these two thresholds can be set based on the desired energy storage cycle efficiency. In special circumstances (such as those requiring emergency power generation or energy storage), the thresholds can be adjusted upward or downward based on actual conditions. At the end of energy release, the volume of high-pressure foam fluid remaining in the formation fracture is greater than or equal to the preset minimum volume threshold, which is equivalent to the pressure in the formation fracture being greater than or equal to the preset minimum pressure at the end of energy release, and the minimum pressure being greater than the closing stress of the formation fracture (i.e., the fracture is still in an open state).

[0108] Finally, in the energy release process of step S3, the high-pressure liquid fluid generates electricity through the preset liquid power generation equipment and the liquid fluid is recovered at the same time; the high-pressure gas fluid (when not air) generates electricity through the preset gas power generation equipment and the gas fluid is recovered at the same time; the recovered liquid fluid and gas fluid can both be used for the configuration of the foam fluid in step S2.

[0109] In some embodiments, if there are multiple target formation fractures, in order to avoid mutual interference caused by different closed pressure fractures during the backflow process, only one group of target formation fractures is allowed to close at the same time during the energy release process, and the high-pressure foam fluid in the fractures at this position is backflowed to the ground and drives the preset power generation equipment to generate electricity.

[0110] like Figure 4 As shown, the system utilizing foam energy storage and release includes: a foam injection device, a backflow pipe, a monitoring device, a blocking device, a gas power generation device and a liquid power generation device. The foam injection device includes a foam generating device, a foam storage device and a pressurized injection pump; the foam generating device, the foam storage device and the pressurized injection pump are connected in sequence, and the pressurized injection pump is connected to the wellbore through an injection pipe to inject high-pressure foam fluid into the wellbore; The foam generating device includes at least one of a venturi foam generator, a gas-liquid mixer, a nozzle foam generator, a mechanical stirring foam generator, and a rotating disk foam generator; Foam generating devices include, but are not limited to, at least one of the following: a Venturi-type foam generator (utilizing the acceleration effect of fluid passing through a Venturi tube to create negative pressure at the narrowest point of the pipe to draw in gas, which is then mixed with the foaming liquid to form foam); a gas-liquid mixer (using a static mixer or a stirrer to forcibly mix gas and foaming liquid to form foam in the pipe); a nozzle-type foam generator (using a nozzle to spray foaming liquid at high speed while simultaneously introducing gas to rapidly mix the liquid into foam during the spraying process); a mechanically agitated foam generator (using an agitator to mechanically stir the foaming liquid and continuously inject gas to form foam in a stirring chamber); and a rotating disk-type foam generator (using a rotating disk to eject the foaming liquid while simultaneously injecting gas to form uniform foam under the action of centrifugal force). The wellbore is connected to the formation fracture; The monitoring device is provided at the wellhead and is used to monitor and determine the parameters of the fluid in the wellhead or wellbore, thereby determining the state of the fluid discharged from the wellhead; The reverse flow pipe is connected to a gas power generation device and a liquid power generation device; the high-pressure liquid fluid generates electricity through the preset liquid power generation device, and the high-pressure gas fluid generates electricity through the preset gas power generation device; the liquid power generation device includes but is not limited to a water turbine, a turbine, etc.; the gas power generation device includes but is not limited to a gas turbine, an expander, etc.; The reverse discharge pipeline is also connected to a separation device, and is then connected to the gas power generation device and the liquid power generation device respectively through the separation device.

[0111] The separation device includes a body for accommodating foam fluid, a foam fluid inlet is provided on one side of the body, and a high-pressure gas fluid outlet and a high-pressure liquid fluid outlet are provided on the other side; a heating module is provided at the bottom of the body and / or a defoaming agent inlet is provided at the top of the body.

[0112] The separation device can separate gas and liquid by changing temperature, centrifugal force, or adding a defoaming agent. However, defoaming agents have significant limitations due to the need for recovery and their impact on re-foaming of the recovered liquid. Therefore, in this technical solution, defoaming is preferably achieved by changing temperature, centrifugal force, or a similar structure (e.g., using a cyclone separator).

[0113] The plugging device is used to close the reverse flow pipeline and plug the wellhead.

[0114] The system also includes a fracturing device for pumping fracturing fluid into the wellbore through a wellbore that reaches the energy storage formation to generate formation fractures in the energy storage formation; The gas power generation device and the liquid power generation device are connected to the power grid. The preset power generation equipment can be connected to the wind power grid or the solar power grid.

[0115] In some embodiments, the plugging device is located within the wellbore. In other embodiments, the plugging device is located on a surface pipeline connected to the wellbore. The specific form of the plugging device in the present invention is not limited, as long as it can seal the wellbore and maintain pressure for energy storage.

[0116] In some embodiments, to prevent hydraulic fractures (i.e., formation fractures) from initiating and propagating in other non-shale formations, the method further includes the step of placing casing in the wellbore above the energy-storage formation. Specifically, the casing is typically cemented in the open-hole wellbore up to the upper portion of the identified burial depth of the energy-storage formation.

[0117] System Example 1: Figure 3 As shown, the system utilizing foam energy storage and release has no separation device. This embodiment is applicable when the foam is configured such that the stable duration T2 of the foam in the formation fracture (i.e., the life span of the high-pressure foam fluid) is less than the energy storage time T3. Specifically, the system includes: a foam injection device, a backflow pipeline, a monitoring device, a plugging device, a gas power generation device, and a liquid power generation device. The foam injection device includes a foam generating device, a foam storage device and a pressurized injection pump; the foam generating device, the foam storage device and the pressurized injection pump are connected in sequence, and the pressurized injection pump is connected to the wellbore through an injection pipe to inject high-pressure foam fluid into the wellbore; Wherein, the foam generating device includes at least one of a venturi foam generator, a gas-liquid mixer, a nozzle foam generator, a mechanical stirring foam generator, and a rotating disk foam generator; The foam generating device includes, but is not limited to, at least one of the following devices: a Venturi-type foam generator (utilizing the acceleration effect of a fluid passing through a Venturi tube to create a negative pressure at the narrowest part of the pipe to draw in gas, which is then mixed with a foaming liquid to form foam); a gas-liquid mixer (using a static mixer or a stirrer to forcibly mix gas and foaming liquid to form foam in the pipe); a nozzle-type foam generator (using a nozzle to spray foaming liquid at high speed while simultaneously introducing gas to rapidly mix the liquid into foam during the spraying process); a mechanical stirring-type foam generator (using a stirrer to mechanically stir the foaming liquid while continuously injecting gas to form foam in a stirring chamber); and a rotating disk-type foam generator (using a rotating disk to eject the foaming liquid while simultaneously injecting gas to form uniform foam under the action of centrifugal force). The wellbore is connected to the formation fracture; The monitoring device is provided at the wellhead and is used to monitor and determine the parameters of the fluid in the wellhead or wellbore, thereby determining the state of the fluid discharged from the wellhead; The reverse discharge pipeline is connected to a gas power generation device and a liquid power generation device; The plugging device is used to close the reverse flow pipeline and plug the wellhead.

[0118] In some embodiments, the system further comprises a fracturing device for pumping fracturing fluid into a wellbore through a wellbore that reaches the energy storage geothermal layer to generate formation fractures in the energy storage geothermal layer.

[0119] The gas power generation device and the liquid power generation device are connected to the power grid. The preset power generation equipment can be connected to the wind power grid or the solar power grid.

[0120] System Example 2: Figure 4 As shown, the difference from system embodiment 1 is that this system utilizing foam energy storage and release is further provided with a separation device based on system embodiment 1. This embodiment is suitable for foam configured to have a stable duration T2 in formation fractures (i.e., the life span of the high-pressure foam fluid) equal to or greater than the energy storage time T3; the backflow pipeline is further connected to a separation device, which is then connected to the gas power generation device and the liquid power generation device respectively through the separation device; The separation device includes a body for accommodating a high-pressure foam fluid, with a foam fluid inlet 1 on one side and a high-pressure gas fluid outlet 2 and a high-pressure liquid fluid outlet 3 on the other side. A heating module 7 is provided at the bottom of the body and / or a defoaming agent inlet 8 is provided at the top of the body. The separation device can separate gas and liquid by changing the temperature, adding a defoaming agent, or using centrifugal force. A large amount of foam fluid 4 accumulates at the foam fluid inlet 1 and, after separation, forms a high-pressure gas fluid 5 and a high-pressure liquid fluid 6. The high-pressure gas fluid 5 moves upward to the high-pressure gas fluid outlet 2, through a pipeline, and enters the gas power generation equipment to generate electricity. The high-pressure liquid fluid 6 moves downward to the high-pressure liquid fluid outlet 3, through a pipeline, and enters the liquid power generation equipment to generate electricity.

[0121] like Figure 5 As shown, in some embodiments, the separation device of the system uses a heating device 7 to change the temperature of the foam to perform gas-liquid separation.

[0122] like Figure 6 As shown, in some embodiments, the separation device of the system performs gas-liquid separation by adding a defoaming agent through a defoaming agent inlet 8 .

[0123] In some embodiments, the separation device of the system can use a heating device and perform gas-liquid separation by adding a defoaming agent.

[0124] System Example 3: The difference from System Example 1 is that Figure 7 As shown, this foam energy storage and release system, based on System Example 1, further includes a liquid storage container, such as a reservoir or tank. The backflow pipeline is also connected to the liquid storage container, which is connected to the gas power generation device and the liquid power generation device. The liquid storage container is used to temporarily store the backflow high-pressure fluid. This embodiment is suitable for foam configurations where the stable duration (i.e., the lifespan of the high-pressure foam fluid) T2 in the formation fracture is less than or equal to the energy storage time T3.

[0125] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0126] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for storing and releasing energy using foam, characterized in that: The specific steps include: S1: Select at least one target formation fracture; S2: injecting high-pressure foam fluid into at least one of the target formation fractures, thereby increasing the pressure of the at least one target formation fracture and widening the fracture; thereby converting the electrical energy into elastic deformation energy of the formation rock and compression energy of the gas in the foam for storage; S3: utilizing the high-pressure fluid discharged from the wellhead during the closing process of at least one of the target formation fractures, and driving corresponding power generation equipment to generate electricity according to the state of the high-pressure fluid to release energy; In step S3, after detecting that there is a demand for power generation, the state of the high-pressure fluid to be discharged is first determined during the closing process. The state of the high-pressure fluid is divided into high-pressure gas fluid, high-pressure liquid fluid and high-pressure foam fluid; When the reversed high-pressure fluid is a high-pressure gas fluid, the reversed high-pressure gas fluid is first used to drive the preset gas power generation equipment to generate electricity; After the high-pressure gas fluid in the wellbore and the target formation fracture is emptied, the remaining high-pressure liquid fluid is reversely discharged, thereby driving the preset liquid power generation equipment to generate electricity; When the high-pressure fluid discharged from the wellhead during the closing process is high-pressure foam fluid, the discharged high-pressure foam fluid is first transported to the separation device for gas-liquid separation, and then the high-pressure liquid fluid and high-pressure gas fluid obtained after separation are used to drive their respective preset corresponding power generation equipment to generate electricity.

2. The method for storing and releasing energy using foam according to claim 1, characterized in that: In step S3, the state of the high-pressure fluid discharged from the wellhead is determined by monitoring the pressure of the high-pressure fluid in the wellhead or wellbore, or / and the density of the high-pressure fluid, or / and the dielectric constant of the high-pressure fluid, or / and the propagation speed of sound waves in the high-pressure fluid; accordingly, If the density of the high-pressure fluid is less than a first preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the density of the high-pressure fluid is greater than a second preset density threshold and less than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; If the density of the high-pressure fluid is greater than a third preset density threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid; Wherein, the first preset density threshold is smaller than the second preset density threshold, and the second preset density threshold is smaller than the third preset density threshold; or, If the dielectric constant of the high-pressure fluid is less than a first preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the dielectric constant of the high-pressure fluid is greater than a second preset dielectric threshold and less than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; If the dielectric constant of the high-pressure fluid is greater than a third preset dielectric threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid; The first preset dielectric threshold is smaller than the second preset dielectric threshold, and the second preset dielectric threshold is smaller than the third preset dielectric threshold; or, If the propagation speed of the sound wave in the high-pressure fluid is less than a first preset sound speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure gas fluid; If the sound wave propagation speed in the high-pressure fluid is greater than a second preset sound speed threshold and less than a third preset sound speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is a high-pressure foam fluid; If the acoustic wave propagation speed of the high-pressure fluid is greater than a third preset acoustic speed threshold, determining that the state of the high-pressure fluid in the wellhead or wellbore is high-pressure liquid; The first preset sound speed threshold is smaller than the second preset sound speed threshold, and the second preset sound speed threshold is smaller than the third preset sound speed threshold.

3. The method for storing and releasing energy using foam according to claim 1, characterized in that: The target formation fracture selected in step S1 includes original formation fractures, and / or at least one formation fracture created by hydraulic fracturing of the formation.

4. The method for storing and releasing energy using foam according to claim 1, characterized in that: In step S2, the high-pressure foam fluid is injected into the target wellbore by driving the injection device with electric energy, and then injected into the target formation fracture through the target wellbore until the pressure of the target formation fracture is greater than the closing pressure of the target formation fracture and less than the expansion pressure of the target formation fracture, and then the injection is stopped; And / or, in step S2, the foam fluid is first prepared at normal temperature and pressure, and then pressurized by a pressurizing device to form a high-pressure foam fluid and injected into the wellbore; And / or, in step S2, based on the injection rate of the high-pressure foam fluid and the depth of the target formation fracture, the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture is calculated; and then the foaming agent and the foam stabilizer are selected according to the type of foam, so that the life time T2 of the high-pressure foam fluid is equal to or greater than the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture, thereby ensuring that the high-pressure foam fluid does not completely break down between the time of being configured and the time of being transported into the target formation fracture.

5. The method for storing and releasing energy using foam according to claim 4, characterized in that: The foam fluid includes at least one of air foam, nitrogen foam and carbon dioxide foam; and / or the foam fluid has a specific gravity of no more than 0.8 after being prepared at normal temperature and pressure.

6. The method for storing and releasing energy using foam according to claim 4, characterized in that: The separation device in step S3 performs gas-liquid separation by changing the temperature or / and adding a defoaming agent or / and centrifugal force; And / or, in step S3, at the end of energy release, the volume of the high-pressure foam fluid remaining in the target formation fracture is greater than or equal to a preset minimum volume threshold; And / or, during the energy release process of step S3, the high-pressure liquid fluid generates electricity through a preset liquid power generation device and the liquid fluid is recovered at the same time; when the high-pressure gas fluid is not air, the gas fluid is generated through a preset gas power generation device and the gas fluid is recovered at the same time; the recovered liquid fluid and gas fluid can both be used for the configuration of the foam fluid in step S2.

7. The method for storing and releasing energy using foam according to claim 4, characterized in that: When the life time T2 of the high-pressure foam fluid is equal to or greater than the time T1 for the high-pressure foam fluid to be transported from the ground to the target formation fracture, and is less than the energy storage time T3, the target formation fracture selected in step S1 is a vertical fracture; during the selection process, whether the formation fracture is a vertical fracture is determined based on the formation stress data or the depth of the formation fracture; Alternatively, when the life time T2 of the high-pressure foam fluid is equal to or greater than the energy storage time T3, the target formation fracture selected in step S1 is a horizontal fracture; during the selection process, whether the formation fracture is a horizontal fracture is determined by formation stress data or the depth of the formation fracture.

8. A system for storing and releasing energy using foam, characterized in that: include: A foam injection device, a backflow pipe, a monitoring device, a blocking device, a separation device, a gas power generation device and a liquid power generation device. The backflow pipe is also connected to a separation device, and the gas power generation device and the liquid power generation device are respectively connected through the separation device; The foam injection device includes a foam generating device, a foam storage device and a pressurized injection pump; the foam generating device, the foam storage device and the pressurized injection pump are connected in sequence, and the pressurized injection pump is connected to the wellbore through an injection pipe to inject high-pressure foam fluid into the wellbore; The wellbore is connected to the formation fracture; The monitoring device is arranged at the wellhead, and is used to monitor and judge the parameters of the fluid in the wellhead or wellbore, so as to judge the state of the high-pressure fluid discharged from the wellhead; the state of the high-pressure fluid is divided into high-pressure gas fluid, high-pressure liquid fluid and high-pressure foam fluid; and when the high-pressure fluid discharged is high-pressure gas fluid, the high-pressure gas fluid discharged is first used to drive the preset gas power generation device to generate electricity; when the high-pressure gas fluid in the wellbore and the target formation cracks is emptied, the remaining high-pressure liquid fluid is discharged, thereby driving the preset liquid power generation device to generate electricity; when the high-pressure fluid discharged from the wellhead during the closing process is high-pressure foam fluid, the high-pressure foam fluid discharged is first transported to the separation device for gas-liquid separation, and then the high-pressure liquid fluid and high-pressure gas fluid obtained after separation are used to respectively drive the respective preset corresponding power generation equipment to generate electricity; The reverse discharge pipeline is connected to a gas power generation device and a liquid power generation device; The plugging device is used to close the reverse flow pipeline and plug the wellhead.

9. The system for storing and releasing energy using foam according to claim 8, characterized in that: The foam generating device includes at least one of a venturi foam generator, a gas-liquid mixer, a nozzle foam generator, a mechanical stirring foam generator, and a rotating disk foam generator; And / or, the separation device comprises a body for accommodating high-pressure foam fluid, a foam fluid inlet being provided on one side of the body, and a high-pressure gas fluid outlet and a high-pressure liquid fluid outlet being provided on the other side; a heating module being provided at the bottom of the body and / or a defoaming agent inlet being provided at the top of the body; And / or, the reverse discharge pipeline is further connected to a liquid storage container, the liquid storage container is connected to the gas power generation device and the liquid power generation device, and the liquid storage container is used to store the reversed high-pressure fluid.

10. The system for storing and releasing energy using foam according to claim 9, characterized in that: The system also includes a fracturing device for pumping fracturing fluid into a wellbore through a wellbore that reaches the energy storage geothermal layer, thereby generating formation fractures in the energy storage geothermal layer.

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