A method for hydrogen energy storage using fracturing fractures of depleted natural gas wells

Abstract

The application discloses a method for hydrogen energy storage by using fracturing cracks of depleted natural gas wells, and comprises the following processes: filling proppants to the tips of main cracks and branch cracks of depleted natural gas wells meeting site selection requirements by using an end sand removal method; injecting hydrogen into the fracturing cracks of the depleted natural gas wells to realize hydrogen storage; and when hydrogen is needed, the hydrogen stored in the fracturing cracks of the depleted natural gas wells is flowed back to the ground surface for utilization. Based on the method, efficient and safe hydrogen storage can be realized, the excess electric energy of a power grid can be consumed, long-time energy storage is realized, and the utilization rate of renewable energy sources is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of new energy storage, and in particular to a method for hydrogen energy storage using fracturing fractures in depleted natural gas wells. Background Technology

[0002] The development of hydrogen storage technology is of paramount importance. With the continuous development of the national economy, hydrogen storage, as a key means of storing clean energy, can effectively address the issue of high volatility in renewable energy and improve energy utilization efficiency. In the energy transition, developing hydrogen storage technology allows for better integration and utilization of large-scale renewable energy sources, promoting the large-scale application of green energy. Simultaneously, hydrogen storage technology can provide a flexible means for energy systems, promoting carbon emission reduction in the power, transportation, and industrial sectors, and contributing to the realization of a low-carbon economy.

[0003] Although the development of hydrogen storage technology is of significant strategic importance to my country's energy development, current conventional hydrogen storage methods, including high-pressure gaseous hydrogen storage, chemical hydrogen storage, and adsorption hydrogen storage, still face considerable technical challenges. First, the cost of hydrogen storage is relatively high, including energy consumption costs during production, storage, and transportation, making it economically uncompetitive in commercial applications. Second, hydrogen has a low density at room temperature and pressure, requiring substantial storage space, which increases storage and transportation costs and limits space utilization. Furthermore, hydrogen's extremely high permeability can easily lead to safety hazards in hydrogen storage facilities, increasing the risks of technology implementation and operation. These issues have become key bottlenecks restricting the development of hydrogen storage technology. Only by overcoming these technical challenges can the widespread application of hydrogen storage technology in the clean energy sector be better promoted. Summary of the Invention

[0004] To address the current technical bottlenecks in hydrogen storage technology, this invention aims to propose a method for hydrogen energy storage using fracturing fractures in depleted natural gas wells. This method enables efficient and safe hydrogen storage, absorbs excess electricity from the power grid, achieves long-term energy storage, and significantly improves the utilization rate of renewable energy.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for hydrogen energy storage using fractures in depleted natural gas wells includes the following steps:

[0007] Propants were used to fill the tips of the main fractures and branch fractures of depleted natural gas wells that meet the site selection requirements using the end-sand removal method.

[0008] Hydrogen is stored by injecting it into the fracturing fractures of a depleted natural gas well.

[0009] When hydrogen is needed, the hydrogen stored in the fractured fissures of depleted natural gas wells is returned to the surface for use.

[0010] Preferably, the conditions under which a depleted natural gas well meets the site selection requirements include:

[0011] The depleted natural gas well has a daily natural gas production of less than 500 cubic meters. 3 / day, no sand production in the wellbore, and the sulfur content of the natural gas is below 20mg / m³. 3 ;

[0012] The gas reservoir is equipped with fracturing fractures, with the main fracture designed to be ≥1500m in length, ≥10m in height, and ≥3500m in depth.

[0013] The gas reservoir has a good natural trap structure and a combination of source, reservoir and cap, with a matrix permeability greater than 0.1 mD, a porosity greater than 10%, and no faults or natural fracture zones.

[0014] Fracturing toughness K of gas reservoir rock IC Requires ≥30MPa·m 1 / 2 ;

[0015] The fracturing fracture has a good shielding layer above and below it, with a shielding layer thickness of more than 3m and a matrix permeability of less than 0.01mD;

[0016] The well casing and cement sheath are in good condition.

[0017] Preferably, the gas reservoir is composed of dense sandstone and carbonate rock.

[0018] Preferably, during the process of injecting hydrogen into the fracturing fractures of a depleted natural gas well:

[0019] The gas pressure within the crack is controlled to be below the net extension pressure of the crack.

[0020] The gas injection rate should not exceed 10m. 3 / min;

[0021] Control the gas injection volume: for volumes less than 500,000 m³ 3 The gas reservoir has a maximum gas injection capacity of 60,000 m³. 3 For volumes greater than 500,000 m³ 3 Less than 1,500,000m 3 The gas reservoir has a maximum injection capacity of 150,000 m³. 3 For volumes greater than 1,500,000 m³ 3 The gas reservoir has a maximum gas injection capacity of 200,000 m³. 3 .

[0022] Preferably, when storing hydrogen, the storage time is controlled to meet the following requirements:

[0023] For volumes less than 500,000 m³ 3 For gas reservoirs, the storage time should not exceed 5 months; for reservoirs with a volume greater than 500,000 m³, the storage time should not exceed 5 months. 3 Less than 1,500,000m 3 For gas reservoirs with a volume greater than 1,500,000 m³, the storage time should not exceed 3 months; 3 The gas reservoir should be stored for no more than two months.

[0024] Preferably, the hydrogen injected into the depleted natural gas well comes from hydrogen produced by electrolysis, and the water source for hydrogen production is formation water from the oilfield site.

[0025] Preferably, the hydrogen stored in the fractured fissures of the depleted natural gas well is returned to the surface via a return pipeline, and gas-water separation is performed. The separated formation water is then used for electrolysis to produce hydrogen.

[0026] Preferably, the backflow pipeline should be inspected and scale cleaned every 45 to 60 days.

[0027] Preferably, the hydrogen discharged back to the ground is first separated into gas and water, and then the separated hydrogen is supplied to a hydrogen-oxygen fuel cell. The hydrogen-oxygen fuel cell uses hydrogen to generate electricity, and the waste heat generated by the power generation of the hydrogen-oxygen fuel cell is stored in a heat storage tank.

[0028] Preferably, during the electrolytic hydrogen production and storage process, the energy flow relationship is that electrical energy is converted into hydrogen energy and the elastic strain energy and stress potential energy of the surrounding rock;

[0029] During the backflow and power generation process, the energy flow relationship involves the conversion of hydrogen energy and the elastic strain energy and stress potential energy of the surrounding rock into electrical energy and thermal energy. This invention has the following beneficial effects:

[0030] In this invention, a method for hydrogen energy storage using fractures in depleted natural gas wells is employed. To prevent the fractures from expanding and causing hydrogen leakage during hydrogen injection, the invention utilizes an end-sand removal method to fill the tips of the main and branch fractures of the depleted natural gas well, which meet the site selection requirements, with proppant. This effectively reduces the energy at the fracture tips during hydrogen injection, preventing fracture extension and propagation. Furthermore, because depleted underground natural gas reservoirs possess excellent pore structures and large storage volumes, and hydrogen storage is highly efficient and safe, avoiding extreme weather and fire hazards, hydrogen generated from surplus electricity can be rapidly stored along the fracture surface into the reservoir's pores and fractures of a specific geometric size through fracturing the depleted gas well. When hydrogen is needed, the stored hydrogen in the depleted natural gas well is returned to the surface for reuse, such as supplying hydrogen-oxygen fuel cells for power generation. Ultimately, this method provides a green and efficient solution to the technical problems of supply and demand imbalance and energy consumption in integrated energy systems. Attached Figure Description

[0031] Figure 1 This is a technical flowchart of the method for hydrogen energy storage using fracturing fractures in depleted natural gas wells, as described in this invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] See Figure 1 The method for hydrogen energy storage using fractured pits in depleted natural gas wells according to the present invention includes the following steps:

[0034] Step (1) The surplus power from the external power grid during off-peak hours or the power from intermittent energy sources such as solar and wind power is transmitted to the electrolyzer device for electrolysis to produce hydrogen. The water source used for hydrogen production in the electrolyzer is the formation water in the oil field. Since the formation water has a high degree of mineralization and strong conductivity, no additional chemical agents need to be added, and hydrogen can be produced directly using the alkaline water electrolysis method.

[0035] Step (2) The hydrogen obtained by electrolysis is injected into the fracturing fracture of the depleted natural gas well through the injection pipeline for temporary storage.

[0036] During the process of injecting hydrogen into the fracturing fracture:

[0037] (1) The gas pressure inside the crack must be strictly controlled below the net extension pressure of the crack to prevent the crack from initiating and expanding.

[0038] (2) The gas injection rate shall not exceed 10m. 3 / min, thereby preventing the unsteady displacement of hydrogen in the pores of the gas storage layer and accelerating the dissolution and diffusion loss of hydrogen;

[0039] (3) The maximum gas storage volume of a gas well is determined by the size of the reservoir. For wells with a volume less than 500,000 m³, the maximum gas storage volume is determined by the size of the reservoir. 3 The gas reservoir has a maximum gas injection capacity of 60,000 m³. 3 For volumes greater than 500,000 m³ 3 Less than 1,500,000m 3 The gas reservoir has a maximum injection capacity of 150,000 m³. 3 For volumes greater than 1,500,000 m³ 3 The gas reservoir has a maximum gas injection capacity of 200,000 m³. 3 ;

[0040] Because hydrogen has high permeability, the storage time of hydrogen injected into the fractures and matrix pores must be limited to prevent large-scale dissipation of hydrogen. Specific requirements are as follows:

[0041] For volumes less than 500,000 m³3 For gas reservoirs with a volume greater than 500,000 m³, the storage time shall not exceed 5 months; 3 Less than 1,500,000m 3 For gas reservoirs with a volume greater than 1,500,000 m³, the storage time shall not exceed 3 months; 3 Gas reservoirs must not be stored for more than 2 months.

[0042] Step (3) During peak electricity consumption periods, hydrogen stored in the fractured cracks of depleted natural gas wells is discharged to the surface gas-water separator device via a return pipeline.

[0043] Step (4) Use a gas-water separation device to separate the gas and formation water, wherein the formation water is recycled to the electrolyzer, and the mixed gas, mainly H2 and containing a very small amount of natural gas, is transported to the fuel cell to provide fuel for the fuel cell.

[0044] Step (5) uses fuel cells to generate electricity to supply the power grid, and the waste heat generated by the power supply is stored in a heat storage tank to provide heat energy for subsequent heating and other heat loads.

[0045] In the above-described scheme of the present invention, the site selection requirements for depleted gas wells used for hydrogen energy storage meet the following conditions:

[0046] (1) Daily natural gas production is less than 500 m³ 3 / day, no sand production in the wellbore, and the sulfur content of the natural gas is below 20mg / m³. 3 .

[0047] (2) The gas reservoir has fracturing fractures, with the main fracture designed to be ≥1500m in length, ≥10m in height, and ≥3500m in depth;

[0048] (3) The preferred gas reservoir is tight sandstone and carbonate rock, which has good natural trap structure and source-storage-cap combination, matrix permeability greater than 0.1mD, porosity greater than 10%, strong pore connectivity, no faults and natural fracture zones, and good gas storage conditions.

[0049] (4) Fracture toughness K of gas reservoir rock IC Requires ≥30MPa·m 1 / 2 This prevents the initiation and propagation of branch cracks and hydraulic cracks;

[0050] (5) The fracturing fracture has a good shielding layer above and below, with a shielding layer thickness of more than 3m and a matrix permeability of less than 0.01mD, which can prevent hydrogen leakage.

[0051] (6) The well casing and cement sheath are in good condition and there is no risk of leakage. The material can effectively resist hydrogen damage.

[0052] In the above-mentioned solution of the present invention, since the hydrogen backflow process will carry pore water from the formation, which will cause certain corrosion to the pipeline, all pipelines must be inspected every 45 to 60 days to remove scale from the pipelines in a timely manner to prevent safety accidents.

[0053] In the above-described scheme of the present invention, the overall energy flow relationship is as follows:

[0054] (1) During the process of electrolytic hydrogen production and injection: electrical energy is converted into hydrogen energy and elastic strain energy and stress potential energy of the surrounding rock;

[0055] (2) During the process of backflow and power generation: hydrogen energy and the elastic strain energy and stress potential energy of the surrounding rock are converted into electrical energy and thermal energy.

[0056] During hydrogen injection, the pressure causes the originally closed fracturing fractures to reopen, thereby applying elastic strain energy and stress potential energy to the rock around the fractures. During the hydrogen return stage, the fracturing fractures gradually close, and the surrounding rock releases its own elastic strain energy and stress potential energy, assisting the gas to return to the surface.

[0057] Example

[0058] This embodiment uses the Chang 6 reservoir in the Changqing Oilfield as a tight sandstone reservoir. During the initial site selection process, 1200 depleted gas wells were investigated, and well X24 was ultimately selected as a gas well suitable for hydrogen storage. After five years of gas production, this well entered a high water-cut period, with a daily production of less than 200 cubic meters. The basic information of this well was investigated in the early stages:

[0059] (1) Hydraulic fracturing operations were carried out in the early stage of the gas reservoir. The main fracture was designed to be 1200m long, 30m high, and the reservoir depth was 3200m.

[0060] (2) The permeability of the gas reservoir matrix is ​​0.2mD, the average porosity is 12%, the scanning electron microscopy results show strong pore connectivity, and the microseismic results inside the reservoir show no faults or natural fracture groups, indicating that the overall gas storage conditions are met.

[0061] (3) Rock mechanics test results of the gas reservoir show that its fracture toughness K IC =32MPa·m 1 / 2 It can prevent the cracks from re-initiating and expanding to a certain extent. The gas reservoir has good mud shielding layers above and below, and the matrix permeability is 0.002mD, which can effectively block the leakage of hydrogen.

[0062] (4) The well logging tools were used to explore the downhole casing and cement sheath, which showed that the casing and cement sheath of the entire well were in good condition and there was no risk of hydrogen leakage.

[0063] (5) The reservoir volume is approximately 1,600,000 m³. 3 The maximum gas injection volume is 200,000 m³.3 ;

[0064] (6) The formation water has a salinity of 25,000 mg / L, and can be directly used for hydrogen production via alkaline water electrolysis.

[0065] Based on the technical guidance of the above-mentioned solution of the present invention, 500m of [unclear text - possibly referring to a specific injection method or injection technique] was first used to inject [unclear text - possibly referring to a specific injection method or injection technique] into the original fracturing fractures of well X24. 3 A 200-mesh ceramic proppant is used to fill the crack tip, preventing the crack from initiating and propagating again. Then, according to... Figure 1 The technical process shown illustrates the construction of an integrated energy system at the well site. The core components of the entire system include: an external power grid, an electrolyzer, a depleted natural gas well, a gas-water separator, a hydrogen-oxygen fuel cell, and a thermal storage tank. The external power grid is connected to the electrolyzer and supplies it with power. The hydrogen outlet of the electrolyzer is connected to the injection pipeline of the depleted natural gas well. The return pipeline of the depleted natural gas well is connected to the gas-water separator on the surface. The outlet of the gas-water separator is connected to the electrolyzer. The gas outlet of the gas-water separator is connected to the hydrogen-oxygen fuel cell. The power transmission end of the fuel cell is connected to the power grid, and the waste heat generated by its power supply is stored in the thermal storage tank.

[0066] The entire integrated energy system underwent its first trial operation in June 2023, initially consuming 8×10 [units of electricity]. 4 kWh, producing approximately 2500m³ of hydrogen. 3 The produced hydrogen was injected into the fractures and matrix pores of well X24 at a rate lower than the net fracture extension pressure for storage. After 50 days of storage, during the peak electricity demand period in July 2023, the underground-stored hydrogen was returned to the surface and used to generate electricity using a fuel cell device, with a final cumulative power generation of 4.56 × 10⁻⁶. 4 kWh, the energy conversion efficiency of the entire system during the initial operation was approximately 57%, and the good performance enabled the long-term safe storage of surplus electricity.

[0067] As can be seen from the above-described solution of the present invention, the present invention has the following characteristics:

[0068] (1) The method provided by this invention can store hydrogen energy efficiently, quickly and safely, and can avoid common safety accidents such as extreme weather and fires; (2) The method provided by this invention can realize green and efficient energy conversion, with very low carbon emissions throughout the process, which is environmentally friendly and solves the technical problems of supply and demand imbalance and surplus power consumption in the current integrated energy system; (3) There are a large number of depleted gas wells in the oil field, which provides favorable conditions for the selection of energy storage sites, and there is no need to build a large number of gas storage tanks. Therefore, the method provided by this invention is more economical than other hydrogen storage methods.

Claims

1. A method for hydrogen energy storage using a fracturing fracture of a depleted natural gas well, characterized by, The method comprises the following processes: Filling proppants to the tip of the main fracture and branch fractures of the depleted natural gas well meeting the site selection requirements by using the end sand-out method; Injecting hydrogen into the fractured fractures of the depleted natural gas well to realize the storage of hydrogen; When hydrogen is needed, the hydrogen stored in the fractured fractures of the depleted natural gas well is flowed back to the surface for utilization; The conditions for the depleted natural gas well meeting the site selection requirements include: The natural gas daily production of the depleted natural gas well is less than 500m 3 / day, the wellbore has no sand production phenomenon, and the sulfur content of the natural gas is less than 20mg / m 3 ; The gas storage layer has fractured fractures, the design length of the main fracture is greater than or equal to 1500 m, the fracture height is greater than or equal to 10 m, and the depth is less than or equal to 3500 m; The gas storage layer has good natural trap structure and source-reservoir-cap assemblage, the matrix permeability is greater than 0.1 mD, the porosity is greater than 10%, and there is no fault and natural fracture zone; Gas reservoir rock fracture toughness K IC Need > 30 MPa•m 1 / 2 ; The fractured fractures have good barrier layers above and below, the thickness of the barrier layers is greater than 3 m, and the matrix permeability is less than 0.01 mD; The quality of the wellbore casing and cement sheath is good; The process of injecting hydrogen into the fractured fractures of the depleted natural gas well includes: Controlling the gas pressure in the fractures to be lower than the net fracture extension pressure; The injection speed is not more than 10 m 3 / min; Control injection volume: for gas reservoirs with volume less than 500000 m 3 , the maximum injection volume is 60000 m 3 ; for gas reservoirs with volume greater than 500000 m 3 , less than 1500000 m 3 , the maximum injection volume is 150000 m 3 ; for gas reservoirs with volume greater than 1500000 m 3 , the maximum injection volume is 200000 m 3 ; The hydrogen injected into the depleted natural gas well comes from electrolytic hydrogen production, and the water source for electrolytic hydrogen production is the formation water on the oilfield site.

2. The method of claim 1, wherein the method is characterized by, The gas storage layer is tight sandstone and carbonate rock.

3. The method of claim 1, wherein the method is characterized by, When hydrogen is stored, the storage time meets the following requirements: for gas reservoirs with a volume less than 500000 m 3 for a storage time of not more than 5 months; for gas reservoirs with a volume greater than 500000 m 3 and less than 1500000 m 3 for a storage time of not more than 3 months; and for gas reservoirs with a volume greater than 1500000 m 3 for a storage time of not more than 2 months.

4. The method of claim 1, wherein the method is characterized by, The hydrogen stored in the fractured fractures of the depleted natural gas well is flowed back to the surface through the flowback pipeline, and gas-water separation is performed, and the separated formation water is used for electrolytic hydrogen production.

5. The method of claim 4, wherein the method further comprises, The flowback pipeline is checked and cleaned every 45-60 days.

6. The method of claim 1, wherein the method further comprises: The hydrogen flowed back to the surface is first subjected to gas-water separation, and then the separated hydrogen is supplied to a hydrogen-oxygen fuel cell, the hydrogen-oxygen fuel cell generates electricity by using hydrogen, and the waste heat generated by the power supply of the hydrogen-oxygen fuel cell is stored in a heat storage tank.

7. The method for hydrogen energy storage by using the fractured fractures of the depleted natural gas well according to claim 6, characterized in that: During electrolytic hydrogen production and storage, the energy flow relationship is that electrical energy is converted into hydrogen energy and elastic strain energy and stress potential energy of the surrounding rock; During flowback and electricity generation, the energy flow relationship is that hydrogen energy and elastic strain energy and stress potential energy of the surrounding rock are converted into electrical energy and thermal energy.

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