A method for carbon dioxide storage and reservoir fracturing transformation

Abstract

A method for carbon dioxide storage and reservoir fracturing transformation, step 1: uniformly mix coal gangue: fly ash: blast furnace slag in a volume ratio of 2:1:1 to form a coal-based solid waste proppant raw material; step 2: pressurize liquid CO2 with a fracturing truck and squeeze it into the formation through a high-pressure oil pipe and a fracturing device to form a complex formation fracture network, and at the same time, use liquid CO2 to replace methane in the formation; step 3: pump the coal-based solid waste proppant raw material into the formation in three batches with a volume fraction of 5%, 7%, and 10%, respectively, to achieve full filling of the complex formation fracture network; step 4: close the wellhead valve, so that the CO2 in the mixed liquid and the coal-based solid waste proppant raw material produce an in-situ mineralization reaction in the formation fracture network to form a high-strength proppant, and at the same time, store the CO2 in the formation fracture network in the form of carbonate; step 5: complete the overall layer operation. The method has simple implementation steps and an ideal fracturing and permeability enhancement effect on the reservoir.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide disposal and utilization, and in particular relates to a carbon dioxide storage and reservoir fracturing transformation method. Background Art

[0002] my country's energy structure is characterized by more coal, less oil, and less gas. Coal, natural gas, etc. will produce a large amount of CO2 when used. The greenhouse effect caused by the large amount of CO2 emissions will have a serious impact on the climate. As my country's first energy consumer, coal consumption accounts for more than 50% of the total primary energy consumption. The large amount of coal consumption determines that my country will produce a large amount of coal-based solid waste when using energy, especially in coal-fired power generation areas and coal-producing areas in the central and western regions. The utilization rate of coal-based solid waste is extremely low. Most of the broken coal gangue, fly ash, slag, etc. can only be piled up in the open air, occupying a large amount of land resources and causing extremely serious environmental pollution.

[0003] my country has abundant unconventional natural gas reserves, and shale gas reserves rank first in the world. Therefore, natural gas, as a clean energy, will become an important energy source to replace coal in the future. The efficient development of unconventional natural gas requires fracturing and permeability enhancement of the reservoir. The current fracturing and permeability enhancement method is mostly hydraulic fracturing. Although this technology has played an important role in the development of unconventional natural gas, hydraulic fracturing has disadvantages such as huge water resource consumption, reservoir clay expansion, and groundwater pollution.

[0004] In summary, my country faces difficulties in the development of coal resources, such as low utilization rate of coal-based solid waste disposal and high CO2 emissions, while the mining of clean energy such as unconventional natural gas faces problems such as excessive consumption of water resources and pollution. Therefore, it is an important measure to achieve effective disposal and utilization of bulk coal-based solid waste and develop green mining technology suitable for unconventional natural gas. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for carbon dioxide storage and reservoir fracturing transformation. The method has simple implementation steps and low implementation cost, and its fracturing and permeability-enhancing effect on the reservoir is ideal. After fracturing, it will not cause problems such as reservoir clay expansion and groundwater pollution. It can simultaneously solve a series of problems existing in the prior art, such as the difficulty in disposing of coal-based solid waste, the inability to effectively seal CO2, and the environmental damage and insufficient reservoir rupture degree in the hydraulic fracturing transformation of unconventional natural gas. It can realize the integrated operation of coal-based solid waste utilization, unconventional natural gas green development and CO2 storage and treatment.

[0006] In order to achieve the above object, the present invention provides a method for carbon dioxide storage and reservoir fracturing, which specifically comprises the following steps:

[0007] The present invention provides a method for carbon dioxide storage and reservoir fracturing transformation, which specifically comprises the following steps:

[0008] Step 1: Prepare proppant raw materials using coal-based solid waste;

[0009] S11: Select three types of coal-based solid wastes, namely, coal gangue, fly ash and blast furnace slag, to make fracturing proppant raw materials;

[0010] S12: crushing the coal gangue, and then screening it, selecting the coal gangue with a particle size of 0.25-0.42 mm for standby; screening the fly ash, selecting the fly ash with a particle size of 0.21 mm for standby; screening the blast furnace slag, selecting the blast furnace slag with a particle size of 0.21 mm for standby;

[0011] S13: uniformly mixing coal gangue, fly ash and blast furnace slag in a volume ratio of 2:1:1 to prepare a multi-source coal-based solid waste proppant raw material;

[0012] Step 2: Liquid CO2 fracturing and seam creation;

[0013] S21: The liquid CO22 in the liquid CO2 storage tank is transported to the fracturing truck. At the same time, the fracturing device connected to the high-pressure oil pipe is lowered into the target reservoir section through the wellbore, and the high-pressure oil pipe is connected to the fracturing truck;

[0014] S22: Using a fracturing truck to pressurize liquid CO2, the liquid CO2 is then squeezed into the fracturing channels connected to the wellbore and the formation fractures connected to the fracturing channels through high-pressure oil pipes and fracturing devices, thereby fracturing the formation to form a complex formation fracture network. In this process, the liquid CO2 is used to fully replace the methane in the formation to increase the permeability of the reservoir;

[0015] Step 3: Liquid CO2 carries the proppant raw material into the formation fracture;

[0016] S31: adding a certain amount of multi-source coal-based solid waste proppant raw material and a certain amount of liquid CO2 into a mixing system, and fully stirring them in the mixing system to form a mixed liquid;

[0017] S32: transporting the mixed liquid to a fracturing truck, pressurizing the mixed liquid by the fracturing truck, and then pumping the mixed liquid into the fracturing channel through a high-pressure oil pipe and a fracturing device;

[0018] S33: Repeating S31 and S32 twice continuously; pumping the multi-source coal-based solid waste proppant raw material prepared in step 1 into the formation in three batches to achieve full filling of the complex formation fracture network, wherein the volume fractions of the three batches of multi-source coal-based solid waste proppant raw materials are 5%, 7%, and 10%, respectively;

[0019] Step 4: in-situ secondary molding of proppant raw materials;

[0020] After the mixed liquid in step 3 is pumped, the wellhead valve is closed to allow the CO2 in the mixed liquid to react with the multi-source coal-based solid waste proppant raw material to produce an in-situ mineralization reaction under high pressure conditions in the formation fracture network. In this process, the Ca and Mg-containing substances in the multi-source coal-based solid waste proppant raw material react with CO2 to generate CaCO3 and MgCO3 minerals, thereby forming a high-strength proppant. At the same time, the CO2 participating in the in-situ mineralization reaction is sealed in the formation fracture network in the form of carbonate, thereby achieving CO2 sealing;

[0021] Step 5: Complete the overall layer operation;

[0022] After completing the first formation operation, move the fracturing tool to the next formation and repeat steps 2 to 4 until all layers are completed with liquid CO2 fracturing and proppant in-situ secondary molding operations.

[0023] Furthermore, in order to ensure a better fracturing effect, in step 2, the fracturing truck pressurizes the liquid CO2 to 70MPa.

[0024] Furthermore, in order to ensure that gas at a higher pressure can be delivered, the high-pressure oil pipe in step 2 can at least withstand a gas pressure of 80 MPa.

[0025] In the present invention, coal gangue with a particle size of 0.25 to 0.42 mm, fly ash with a particle size of 0.21 mm, and blast furnace slag with a particle size of 0.21 mm are selected as raw materials for proppants, which can not only ensure that the transportation process of the raw materials is smoother and more convenient, but also ensure that the subsequent in-situ mineralization reaction between the proppant raw materials and CO2 is more sufficient, so that a larger amount of high-strength proppants can be generated, and at the same time, it is conducive to realizing the sealing operation of a larger amount of CO2. First, the liquid CO2 is pressurized for energy storage, and then the pressurized liquid CO2 is used to fractur the formation. Compared with hydraulic fracturing, this method can more easily form a complex formation fracture network in the formation, and after fracturing, it will not cause problems such as reservoir clay expansion and groundwater pollution. At the same time, the pressurized liquid CO2 can also replace the methane in the formation more fully, thereby significantly improving the permeability and production-increasing transformation effect of the formation, which is conducive to increasing the extraction efficiency of unconventional natural gas. In the process of using liquid CO2 to carry proppant raw materials into formation fractures, multi-source coal-based solid waste proppant raw materials are pumped into the fracturing channel in three batches at a volume ratio of 5%, 7%, and 10%, respectively, which can achieve full filling of complex fracture networks. At the same time, subsequent larger amounts of injection can be used to drive the previously entered mixed liquid to move to deeper fractures, thereby effectively ensuring that the fractures generated by fracturing will not heal, further improving the effect of permeability and production enhancement. By using the CO2 in the mixed liquid and the Ca and Mg-containing substances in the proppant raw materials to undergo in-situ mineralization reactions under high pressure conditions in formation fractures and form high-strength proppants, a proppant that can bear greater pressure can be obtained, which can have a better supporting effect, so that the fractures generated by fracturing can be better supported. At the same time, this method can also allow the CO2 involved in the reaction to be sealed in the formation fracture network in the form of carbonates, effectively realizing the CO2 sealing operation.

[0026] The present invention first uses liquid CO2 to carry out green fracturing transformation of unconventional natural gas reservoirs to achieve increased production and permeability, and then injects coal-based solid waste and CO2 as proppant raw materials into the fracturing cracks for in-situ mineralization reaction to form high-strength proppants that can withstand greater pressure. This solves a series of problems existing in the prior art, such as the difficulty in disposing of coal-based solid waste, the inability to effectively seal CO2, and the environmental damage and insufficient reservoir rupture caused by hydraulic fracturing transformation of unconventional natural gas, thereby realizing the integrated operation of coal-based solid waste utilization, green development of unconventional natural gas and CO2 storage and treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the state of liquid CO2 fracturing and seam creation in the present invention;

[0028] Figure 2 It is a schematic diagram of the state in which liquid CO2 carries proppant raw materials into formation fractures in the present invention;

[0029] Figure 3 Schematic diagram of the state of in-situ secondary molding of the proppant in the present invention;

[0030] Figure 4 It is a schematic diagram of the state of completing the overall layer section operation in the present invention.

[0031] In the figure: 1. Liquid CO2 storage tank, 2. Liquid CO2, 3. Fracturing truck, 4. High-pressure oil pipe, 5. Fracturing device, 6. Wellbore, 7. Fracturing channel, 8. Formation fractures, 9. Complex formation fracture network, 10. Mixing system, 11. Mixed liquid, 12. High-strength proppant. DETAILED DESCRIPTION

[0032] The present invention provides a method for carbon dioxide storage and reservoir fracturing transformation, which first uses liquid CO2 to carry out green fracturing transformation on unconventional natural gas reservoirs to achieve production and permeability enhancement, and then injects coal-based solid waste and CO2 into the fracturing cracks to carry out in-situ mineralization reaction to form high-strength proppant, thereby realizing the treatment and utilization of coal-based solid waste while storing CO2, solving a series of problems existing in the prior art, such as the difficulty in disposing coal-based solid waste, the inability to effectively store CO2, and the environmental damage caused by hydraulic fracturing of unconventional natural gas, and realizing the integrated operation of coal-based solid waste utilization, green development of unconventional natural gas and CO2 storage, and specifically comprising the following steps;

[0033] Step 1: Prepare proppant raw materials using coal-based solid waste;

[0034] S11: Select three types of coal-based solid wastes, namely, coal gangue, fly ash and blast furnace slag, to make fracturing proppant raw materials;

[0035] S12: crushing the coal gangue, and then screening it, selecting the coal gangue with a particle size of 0.25-0.42 mm for standby; screening the fly ash, selecting the fly ash with a particle size of 0.21 mm for standby; screening the blast furnace slag, selecting the blast furnace slag with a particle size of 0.21 mm for standby;

[0036] Since the in-situ mineralization reaction between proppant raw materials and CO2 is affected by the particle size of the raw materials, and too large a particle size is not conducive to transportation operations, and the initial particle size of coal gangue is large, it is necessary to crush the coal gangue first, while the initial particle size of fly ash and blast furnace slag is small, so no additional treatment is required;

[0037] S13: uniformly mixing coal gangue, fly ash and blast furnace slag in a volume ratio of 2:1:1 to prepare a multi-source coal-based solid waste proppant raw material;

[0038] Step 2: Liquid CO2 fracturing and seam creation;

[0039] S21: Figure 1As shown, the liquid CO22 in the liquid CO2 storage tank 1 is transported to the fracturing vehicle 3, and at the same time, the fracturing device 5 connected to the high-pressure oil pipe 4 is lowered into the target reservoir section through the wellbore 6, and the high-pressure oil pipe 4 is connected to the fracturing vehicle 3;

[0040] S22: After the liquid CO22 is pressurized by the fracturing truck 3, it is squeezed into the fracturing channel 7 connected to the wellbore 6 and the formation fracture 8 connected to the fracturing channel 7 through the high-pressure oil pipe 4 and the fracturing device 5, thereby fracturing the formation to form a complex formation fracture network 9. In this process, the liquid CO22 is used to fully replace the methane in the formation to increase the permeability of the reservoir;

[0041] Step 3: Liquid CO2 carries the proppant raw material into the formation fracture;

[0042] S31: Figure 2 As shown, a certain amount of multi-source coal-based solid waste proppant raw material and a certain amount of liquid CO22 are added to the mixing system 10, and the mixing system 10 is used to fully stir them to form a mixed liquid 11;

[0043] S32: transporting the mixed liquid 11 to the fracturing vehicle 3, pressurizing the mixed liquid 11 by the fracturing vehicle 3, and then pumping the mixed liquid 11 into the fracturing channel 7 through the high-pressure oil pipe 4 and the fracturing device 5;

[0044] S33: Repeat S31 and S32 twice continuously; pump the multi-source coal-based solid waste proppant raw material prepared in step 1 into the formation in three batches to achieve full filling of the complex formation fracture network 9, wherein the volume fractions of the three batches of multi-source coal-based solid waste proppant raw materials are 5%, 7%, and 10%, respectively. A large number of experiments have shown that the use of this gradient increase pumping method can significantly improve the support effect of the fracture;

[0045] Step 4: in-situ secondary molding of proppant raw materials;

[0046] like Figure 3 As shown, after the mixed solution 11 in step 3 is pumped, the wellhead valve is closed, so that the CO2 in the mixed solution 11 and the multi-source coal-based solid waste proppant raw material produce an in-situ mineralization reaction under high pressure conditions in the formation fracture network. In this process, the substances containing Ca and Mg in the multi-source coal-based solid waste proppant raw material react with CO2 to generate minerals (carbonates) such as CaCO3 and MgCO3, thereby forming a high-strength proppant 12. At the same time, the CO2 participating in the in-situ mineralization reaction is sealed in the formation fracture network in the form of carbonate, thereby achieving CO2 sealing;

[0047] Step 5: Complete the overall layer operation;

[0048] After completing the first formation operation, move the fracturing tool to the next formation and repeat steps 2 to 4 until the operation is completed. Figure 4 Liquid CO2 fracturing and in-situ proppant secondary molding operations are shown in all layers.

[0049] In order to ensure a better fracturing effect, in step 2, the fracturing truck 3 pressurizes the liquid CO22 to 70 MPa.

[0050] In order to ensure that gas with higher pressure can be delivered, the high-pressure oil pipe 4 in step 2 can at least withstand a gas pressure of 80 MPa.

[0051] In the present invention, coal gangue with a particle size of 0.25 to 0.42 mm, fly ash with a particle size of 0.21 mm, and blast furnace slag with a particle size of 0.21 mm are selected as raw materials for proppants, which can not only ensure that the transportation process of the raw materials is smoother and more convenient, but also ensure that the subsequent in-situ mineralization reaction between the proppant raw materials and CO2 is more sufficient, so that a larger amount of high-strength proppants can be generated, and at the same time, it is conducive to realizing the sealing operation of a larger amount of CO2. First, the liquid CO2 is pressurized for energy storage, and then the pressurized liquid CO2 is used to fractur the formation. Compared with hydraulic fracturing, this method can more easily form a complex formation fracture network in the formation, and after fracturing, it will not cause problems such as reservoir clay expansion and groundwater pollution. At the same time, the pressurized liquid CO2 can also replace the methane in the formation more fully, thereby significantly improving the permeability and production-increasing transformation effect of the formation, which is conducive to increasing the extraction efficiency of unconventional natural gas. In the process of using liquid CO2 to carry proppant raw materials into formation fractures, multi-source coal-based solid waste proppant raw materials are pumped into the fracturing channel in three batches at a volume ratio of 5%, 7%, and 10%, respectively, which can achieve full filling of complex fracture networks. At the same time, subsequent larger amounts of injection can be used to drive the previously entered mixed liquid to move to deeper fractures, thereby effectively ensuring that the fractures generated by fracturing will not heal, further improving the effect of permeability and production enhancement. By using the CO2 in the mixed liquid and the Ca and Mg-containing substances in the proppant raw materials to undergo in-situ mineralization reactions under high pressure conditions in formation fractures and form high-strength proppants, a proppant that can bear greater pressure can be obtained, which can have a better supporting effect, so that the fractures generated by fracturing can be better supported. At the same time, this method can also allow the CO2 involved in the reaction to be sealed in the formation fracture network in the form of carbonates, effectively realizing the CO2 sealing operation.

[0052] The present invention first uses liquid CO2 to carry out green fracturing transformation of unconventional natural gas reservoirs to achieve increased production and permeability, and then injects coal-based solid waste and CO2 as proppant raw materials into the fracturing cracks for in-situ mineralization reaction to form high-strength proppants that can withstand greater pressure. This solves a series of problems existing in the prior art, such as the difficulty in disposing of coal-based solid waste, the inability to effectively seal CO2, and the environmental damage and insufficient reservoir rupture caused by hydraulic fracturing transformation of unconventional natural gas, thereby realizing the integrated operation of coal-based solid waste utilization, green development of unconventional natural gas and CO2 storage and treatment.

Claims

1. A method for carbon dioxide storage and reservoir fracturing, characterized in that: Specifically include the following steps: Step 1: Prepare proppant raw materials using coal-based solid waste; S11: Select three types of coal-based solid wastes, namely, coal gangue, fly ash and blast furnace slag, to make fracturing proppant raw materials; S12: crushing the coal gangue, and then screening it, selecting the coal gangue with a particle size of 0.25-0.42 mm for standby; screening the fly ash, selecting the fly ash with a particle size of 0.21 mm for standby; screening the blast furnace slag, selecting the blast furnace slag with a particle size of 0.21 mm for standby; S13: uniformly mixing coal gangue, fly ash and blast furnace slag in a volume ratio of 2:1:1 to prepare a multi-source coal-based solid waste proppant raw material; Step 2: Liquid CO2 fracturing and seam creation; S21: The liquid CO2 (2) in the liquid CO2 storage tank (1) is transported to the fracturing vehicle (3), and at the same time, a fracturing device (5) connected to a high-pressure oil pipe (4) is lowered to the target reservoir section through a wellbore (6), and the high-pressure oil pipe (4) is connected to the fracturing vehicle (3); S22: After the liquid CO2 (2) is pressurized by a fracturing vehicle (3), it is squeezed into a fracturing channel (7) connected to a wellbore (6) and a formation fracture (8) connected to the fracturing channel (7) through a high-pressure oil pipe (4) and a fracturing device (5), thereby fracturing the formation to form a complex formation fracture network (9). In this process, the liquid CO2 (2) is used to fully replace the methane in the formation, so as to enhance the permeability of the reservoir; Step 3: Liquid CO2 carries the proppant raw material into the formation fracture; S31: adding a certain amount of multi-source coal-based solid waste proppant raw material and a certain amount of liquid CO2 (2) into a mixing system (10), and fully stirring them using the mixing system (10) to form a mixed liquid (11); S32: transporting the mixed liquid (11) to the fracturing vehicle (3), pressurizing the mixed liquid (11) by the fracturing vehicle (3), and then pumping the mixed liquid (11) into the fracturing channel (7) through the high-pressure oil pipe (4) and the fracturing device (5); S33: Repeating S31 and S32 twice continuously; pumping the multi-source coal-based solid waste proppant raw material prepared in step 1 into the formation in three batches to achieve full filling of the complex formation fracture network (9), wherein the volume fractions of the three batches of multi-source coal-based solid waste proppant raw materials are 5%, 7%, and 10%, respectively; Step 4: in-situ secondary molding of proppant raw materials; After the mixed solution (11) in step 3 is pumped, the wellhead valve is closed to allow the CO2 in the mixed solution (11) to react with the multi-source coal-based solid waste proppant raw material to produce an in-situ mineralization reaction under high pressure conditions in the formation fracture network. In this process, the Ca and Mg-containing substances in the multi-source coal-based solid waste proppant raw material react with CO2 to generate CaCO3 and MgCO3 minerals, thereby forming a high-strength proppant. At the same time, the CO2 participating in the in-situ mineralization reaction is sealed in the formation fracture network in the form of carbonate, thereby achieving CO2 sealing; Step 5: Complete the overall layer operation; After completing the first formation operation, move the fracturing tool to the next formation and repeat steps 2 to 4 until all layers are completed with liquid CO2 fracturing and proppant in-situ secondary molding operations.

2. A method for carbon dioxide storage and reservoir fracturing according to claim 1, characterized in that: In step 2, the fracturing truck (3) pressurizes the liquid CO2 (2) to 70 MPa.

3. A method for carbon dioxide storage and reservoir fracturing according to claim 1 or 2, characterized in that: The high-pressure oil pipe (4) in step 2 can withstand a gas pressure of at least 80 MPa.

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