Deep coal seam CO2 fracturing, displacement yield increasing and sealing integrated method

Abstract

The invention discloses a deep coal seam CO2 fracturing, displacement yield increasing and sealing integrated method, and belongs to the technical field of petroleum and natural gas science and engineering and environmental science and engineering. Supercritical CO2 and clear water containing a tracer agent are alternately injected into a target coal seam till a main fracture is communicated with an injection well and a production well, after clear water fracturing fluid is flowback, guar gum fracturing fluid containing a propping agent is injected into a stratum, and then the guar gum fracturing fluid is flowback to the ground; and hydrophobic modified fluid is injected into the target coal seam, soaking operation is conducted, and after soaking operation is finished, the hydrophobic modified fluid is flowback to the ground. During the production of the coal bed gas, the production is suspended when the CO2 concentration in the produced gas reaches a threshold value. And after quantitative hydrophobic modified fluid and supercritical CO2 are sequentially injected into the shaft, soaking operation is carried out, and after soaking operation is finished, hydrophobic modified fluid flowback is carried out. And repeating the steps until the accumulated yield increment of the coalbed methane reaches a threshold value, and stopping production. And hydrophobic modified fluid, liquid / supercritical CO2 and hydrophilic modified fluid are sequentially injected into the shaft, the injection well is closed, and well shut-in operation is carried out. The technology can break through crustal stress limitation, multi-directional fracturing is achieved, a multi-stage three-dimensional fracture net is formed, and the coal bed gas recovery rate and the CO2 storage rate are improved while large-scale transformation of the reservoir is achieved.

Description

Technical Field

[0001] This invention belongs to the fields of petroleum and natural gas science and engineering and environmental science and engineering technology, specifically relating to an integrated method for deep coal seam CO2 fracturing, displacement and production enhancement and storage. Background Technology

[0002] The existing coalbed methane development technology system is only applicable to some coal seams and urgently needs to be supplemented and improved.

[0003] The prerequisite for developing coalbed methane is the effective modification of coal seams. Traditional coal seam modification technologies involve mechanically fracturing or acid fracturing to destroy the coal seam structure and release the coalbed methane contained within the pore spaces, thus achieving effective modification. However, these technologies have high production costs and limited scope of application. Supercritical CO2 fracturing technology can overcome geostress limitations, has lower initiation pressure, and easily forms complex fracture networks, allowing for a larger modification area and compensating for the shortcomings of traditional coal seam modification technologies to some extent. However, single supercritical CO2 fracturing technology has drawbacks such as small main fracture opening, high fracture surface roughness, and a large amount of debris within the fractures, requiring further improvements. In addition, the technology provided by this invention patent, besides effectively modifying coal seams and increasing coalbed methane production, can also assist in CO2 sequestration in coal seams. Summary of the Invention

[0004] To solve or partially solve the problems existing in related technologies, the present invention provides an integrated method for deep coal seam CO2 fracturing, displacement and production enhancement and storage.

[0005] This invention provides an integrated method for CO2 fracturing, displacement and production enhancement, and storage in deep coal seams, comprising the following steps: S1. Supercritical CO2 is injected into the target coal seam as a pre-fracturing fluid to form a complex fracture network in the target coal seam. After the predetermined injection volume is reached, the injection is stopped. Then, water containing tracer is injected into the target coal seam to continue fracturing the reservoir. After the main fractures reach the target length, the injection is stopped. The predetermined injection volume needs to be determined comprehensively based on the actual formation conditions and the construction process parameters obtained from laboratory experiments and numerical simulations.

[0006] S2, repeat step S1, alternately inject supercritical CO2 and water containing tracer. During the injection, monitor the location, length and extension direction of the main fractures based on the seismic waves and tracer location, and adjust the injection parameters in a timely manner until the main fractures are connected to the injection well and production well of the target reservoir. S3, after opening the production well and backflowing the water fracturing fluid containing tracer, inject the guar gum fracturing fluid containing proppant into the target coal seam as the sand-carrying fracturing fluid. After the proppant settles to the fracture surface, backflow the sand-carrying fracturing fluid to the surface. S4. Inject hydrophobic modified fluid into the target coal seam to adjust the coal seam to hydrophobicity and then perform well shut-in operation; after the well shut-in is completed, open the production well to discharge the hydrophobic modified fluid and produce coalbed methane. S5: During coalbed methane production, the gas production in the wellbore is monitored at all times. When the CO2 concentration in the produced gas reaches the threshold, the well is shut down and production is suspended. S6, inject hydrophobic modified fluid and liquid supercritical CO2 into the wellbore in sequence, and then carry out well shut-in operation. After the well shut-in is completed, open the wellbore to carry out the return flow of hydrophobic modified fluid and coalbed methane production. S7. Repeat step S6 until the cumulative increase in coalbed methane production of the target coal seam reaches the threshold and then stop production. S8, inject hydrophobic modified fluid, liquid supercritical CO2 and hydrophilic modified fluid into the wellbore in sequence, close the injection well and carry out well sealing operation.

[0007] Preferably, the target length of the main fracture is 10%-25% of the reference distance; the reference distance is the shortest straight-line distance between the injection wellbore and the production wellbore of the same target reservoir.

[0008] Preferably, the injection parameters include injection temperature, injection pressure, injection mass, and injection rate.

[0009] Preferably, the concentration of the water containing the tracer is 10-20 ppm; the tracer is ammonium thiocyanate or tritium water.

[0010] Preferably, the mass fraction of proppant in the proppant-containing fracturing fluid is 5%-15%; the proppant is quartz sand or ceramsite, and the particle size of the proppant is adjusted according to the opening of the main fracture.

[0011] Preferably, the preparation method of the hydrophobic modified fluid includes the following steps: surface grafting modification of nanoparticles using a silane coupling agent, and then soaking the modified nanoparticles in a hydrophobic polymer solution with a mass fraction of 2%-5% for 12-36 hours to obtain the hydrophobic modified fluid; the soaking temperature is 30-60℃.

[0012] The surface grafting modification of nanoparticles using silane coupling agents specifically includes: (1) soaking and cleaning the nanoparticles in a 10-20%wt acetic acid solution prepared with deionized water for 4-6 hours, then taking out the nanoparticles and vacuum drying them at 100-120℃ for 1-3 hours; (2) preparing a silane coupling agent solution with a molar concentration of 0.1-0.25mol / L using deionized water, heating the solution at room temperature to 50℃ for 1-3 hours, and adding a small amount of acetic acid solution, the amount of acetic acid being... (3) Add the pretreated nanoparticles to the hydrolyzed silane coupling agent solution, place the solution in a magnetic stirrer, set the speed to 1200-2000 r / min, the temperature to 50-80℃, stir for 5-10 h, and introduce N2 throughout the stirring process; (4) Filter the solution, soak the separated nanoparticles in deionized water for 2-5 h, take them out and place them in a vacuum oven to dry at room temperature-45℃ for 0.5-1.5 h.

[0013] Preferably, the nanoparticles are any one of silicon dioxide, titanium dioxide, Fe2O3, and aluminum oxide; the hydrophobic polymer is any one of epoxy resin, urea-formaldehyde, polyurethane, phenolic resin, and furfural alcohol; and the silane coupling agent is any one of vinylsilane, aminosilane, methacryloxysilane, and epoxysilane.

[0014] Preferably, in step S5, when the volume concentration of CO2 in the produced gas reaches 90%, the well is shut off and production is suspended.

[0015] Preferably, in step S7, production is stopped when the cumulative increase in coalbed methane production of the target coal seam is less than 5%.

[0016] Preferably, the hydrophilic modified fluid is a dispersion of nanoparticles with a mass fraction of 5-10% formed by thoroughly stirring silica nanoparticles or alumina nanoparticles in water.

[0017] The technical solution provided by this invention has the following beneficial effects: This invention can overcome the limitations of geostress, induce fracturing in multiple directions, and form a multi-level three-dimensional fracture network, enabling large-scale reservoir stimulation. Compared with traditional coal seam stimulation technologies, it has a larger stimulation volume, produces fractures with lower surface roughness and fewer blockages, resulting in less damage to the reservoir. It also reduces the risk of formation contamination and the difficulty of post-fracturing flowback fluid treatment, achieving good water-saving and environmental protection effects. Through constructing coalbed methane migration channels, reducing seepage resistance, competitive adsorption and replacement of CO2 and coalbed methane, and replenishing formation energy, it significantly improves coalbed methane recovery. Furthermore, it ensures the injectability and long-term safety of carbon dioxide geological sequestration, resulting in significant economic and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the integrated process of deep coal seam CO2 fracturing, displacement and production enhancement, and storage in Embodiment 1 of the present invention. Detailed Implementation

[0019] Example 1 A method integrating CO2 fracturing, displacement and production enhancement, and storage in deep coal seams includes the following steps: (1) Coal seam fracturing stage S1, supercritical CO2 is injected into the target coal seam as a pre-fracturing fluid to form a complex fracture network within the target coal seam, achieving the predetermined injection volume (50-10). 3 After injecting (tons), stop the injection. Inject 20 ppm of water containing ammonium thiocyanate tracer into the target coal seam and continue fracturing the reservoir. Once the main fracture reaches the target length (generally 5-20m, 20m in this example), stop the injection. Repeat the above steps, alternately injecting supercritical CO2 and water containing tracer, until the formed main fracture can connect the injection well and production well of the target reservoir.

[0020] S2, open the production well and perform water fracturing fluid flowback. Inject proppant-containing guar gum fracturing fluid (in this example, the proppant is high-strength ceramsite, the sand ratio is 20%, and the mass fraction of proppant in the proppant-containing guar gum fracturing fluid is 10%) into the target coal seam as the proppant-carrying fracturing fluid. The injection volume of guar gum fracturing fluid is generally 500-5000 m³. 3 In this embodiment, the injection volume of guar gum fracturing fluid is 500m³. 3 Then, the fracturing fluid carrying sand is returned to the ground.

[0021] (2) Enhanced coalbed methane extraction stage S3, the preparation method of hydrophobic modified fluid includes the following steps: (1) Use deionized water to prepare a 20%wt acetic acid solution to soak and clean the nanoparticles for 4h, take out the nanoparticles and vacuum dry them at 120℃ for 3h; (2) Use deionized water to prepare a vinylsilane solution with a molar concentration of 0.25mol / L, heat the solution at room temperature for 3h, add a small amount of acetic acid solution, the amount of acetic acid is 15% of the amount of vinylsilane; (3) Add the pretreated nanoparticles to the hydrolyzed vinylsilane solution, add the solution to a magnetic stirrer, set the speed to 2000r / min, the temperature to 80℃, stir for 5h, and introduce N2 throughout the stirring process; (4) Filter the solution, soak the separated nanoparticles in deionized water for 5h, take them out and place them in a vacuum oven to dry at room temperature-45℃ for 1.5h to obtain the modified nanoparticles. (5) The modified nanoparticles were soaked in an epoxy resin solution with a mass fraction of 5% for 36 hours to obtain a hydrophobic modified fluid; the soaking temperature was 60℃.

[0022] S4, inject 2000m into the target coal seam. 3 The epoxy resin hydrophobic modified fluid is used to adjust the coal seam to be hydrophobic before the coal seam is sealed. After the sealing is completed, the production well is opened to discharge the hydrophobic modified fluid and produce coalbed methane.

[0023] The process involves returning the injected hydrophobic modified fluid to the ground and measuring the concentration of hydrophobic surfactant in the returned fluid until it reaches a certain stable value in the region. This demonstrates that the hydrophobic surfactant remains in the coal seam, indicating that the coal seam has become hydrophobic.

[0024] S5. During coalbed methane production, the wellbore's gas production is constantly monitored. When the CO2 volume concentration in the produced gas reaches the threshold (90%), the well is shut off to suspend production. Hydrophobic modified fluid and supercritical CO2 are sequentially injected into the wellbore, followed by well shut-in. After shut-in, the wellbore is opened for the return of the hydrophobic modified fluid and coalbed methane production. These steps are repeated until the cumulative increase in coalbed methane production from the target coal seam reaches the threshold (less than 5%), at which point production is stopped.

[0025] (3) CO2 coal seam sealing stage S6, inject 2000m into the wellbore sequentially. 3 Hydrophobically modified fluid with a concentration of 3000 ppm, 100,000 t of liquid / supercritical CO2 and 3000 m 3 A hydrophilic modified fluid with a concentration of 3000 ppm was used to shut down the injection well for well sealing operations. This hydrophilic modified fluid can adjust the wettability of the target shale gas reservoir to a hydrophilic state. The hydrophilic modified fluid is formed by thoroughly stirring silica nanoparticles in water to create a nanoparticle dispersion with a mass fraction of 10%.

[0026] In this embodiment, the selection of the target coalbed methane reservoir specifically includes the following steps: S1-1-1, Reservoir Geological Evaluation: Based on seismic measurement data and well logging data, the reservoir is characterized in detail to understand the reservoir thickness, pore-fracture characteristics, fluid characteristics, and coalbed methane occurrence characteristics. The production potential of the reservoir is systematically evaluated, and the target coal seam is preliminarily screened.

[0027] S1-1-2, Reservoir Characteristic Analysis: By sampling and laboratory analysis in the sweet spot area, parameters such as material composition, mineral structure, mechanical characteristics, porosity, permeability, and isothermal adsorption curve of the reservoir coal are determined, and coalbed methane sweet spots suitable for CO2 fracturing and storage are selected as target reservoirs.

[0028] S1-1-3, an ideal sweet spot for coalbed methane suitable for CO2 fracturing and storage typically possesses the following characteristics: medium or high coal rank, high gas content, high permeability, overpressure or normal pressure, high adsorption capacity, undersaturation, great depth, good sealing, thick and stable coal seams, simple structure, moderate burial depth, and favorable surface conditions. In actual exploration, it is difficult to perfectly meet all conditions; therefore, permeability and gas content must be used as the most important evaluation indicators for a balanced assessment based on the specific circumstances.

[0029] In this embodiment, the fracturing of the reservoir specifically includes the following steps: S1-2-1 uses seismic test data, well logging curves, geological data, and relevant parameters of target reservoir samples obtained in the laboratory to construct a three-dimensional geological model. Various construction parameters are then adjusted to conduct reservoir fracturing simulation experiments. Based on the experimental results, optimal construction parameters (such as the predetermined CO2 injection volume in the CO2 fracturing stage and the target length of the main fractures in the clear water fracturing stage) are selected to guide production.

[0030] S1-2-2 monitors the location of the tracer and microseismic signals in real time to determine important parameters such as the location, aperture, and extension direction of the fractures. It also adjusts important parameters such as the volume, pressure, and temperature of the injected fluid, focusing on controlling the aperture, length, and extension direction of the main fractures until the entire fracturing process is completed.

[0031] Specifically: P110 corrosion-resistant casing with an epoxy coating was used, and horizontal wells were perforated in sections (50-100m each). First, a small-scale test fracturing (DFIT) was performed to determine the fracturing pressures of CO2 and water. Pure supercritical CO2 (pressure > 7.38MPa, temperature > 31℃) was injected at a flow rate of 10-20 m³ / min, with a single-section volume of 500-1500 m³, and the injection pressure was 1.2 times the CO2 fracturing pressure. The pre-fracturing fluid accounted for 40% of the total volume. Then, CO2 containing low-density ceramic proppant (40 mesh) with a sand ratio of 5% was injected. During the main fracturing stage, proppant was added in a stepped manner, and microseismic monitoring was used to track fracture propagation in real time. CO2 injection was stopped once the fracture reached the target distance. Water was then injected into the coal seam at a flow rate of 10 m³ / min, with a single-section volume of 500 m³. 3 The injection pressure is 1.2 times the fracturing pressure of pure water, and the pre-fracturing fluid accounts for 30%. Pure water containing high-strength ceramic particles as proppant (60 mesh size) with a sand ratio of 10% is then injected. During the main fracturing stage, proppant is added in a stepped manner, and microseismic monitoring is used to track fracture propagation in real time. Once the fracture reaches the target distance, pure water injection is stopped. The above steps are repeated until a through fracture appears.

[0032] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method integrating CO2 fracturing, displacement and production enhancement, and sequestration in deep coal seams, characterized in that: Includes the following steps: S1. Supercritical CO2 is injected into the target coal seam as a pre-fracturing fluid to form a complex fracture network in the target coal seam. After the predetermined injection volume is reached, the injection is stopped. Then, water containing tracer is injected into the target coal seam to continue fracturing the reservoir. After the main fractures reach the target length, the injection is stopped. S2, repeat step S1, alternately inject supercritical CO2 and water containing tracer. During the injection, monitor the location, length and extension direction of the main fractures based on the seismic waves and tracer location, and adjust the injection parameters in a timely manner until the main fractures are connected to the injection well and production well of the target reservoir. S3, after opening the production well and backflowing the water fracturing fluid containing tracer, inject the guar gum fracturing fluid containing proppant into the target coal seam as the sand-carrying fracturing fluid. After the proppant settles to the fracture surface, backflow the sand-carrying fracturing fluid to the surface. S4, inject hydrophobic modified fluid into the target coal seam, adjust the coal seam to be hydrophobic, and then perform well-clogging operation on the coal seam; After the well is shut down, the production well is opened to discharge the hydrophobic modified fluid and produce coalbed methane. S5: During coalbed methane production, the gas production rate of the production well is monitored at all times. When the CO2 concentration in the produced gas reaches the threshold, the well is shut down and production is suspended. S6, inject hydrophobic modified fluid and liquid supercritical CO2 into the wellbore in sequence, and then carry out well shut-in operation. After the well shut-in is completed, open the wellbore to carry out the return flow of hydrophobic modified fluid and coalbed methane production. S7. Repeat step S6 until the cumulative increase in coalbed methane production of the target coal seam reaches the threshold and then stop production. S8, inject hydrophobic modified fluid, liquid supercritical CO2 and hydrophilic modified fluid into the wellbore in sequence, close the injection well and carry out well sealing operation.

2. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: The target length of the main fracture is 10%-25% of the reference distance; the reference distance is the shortest straight-line distance between the injection wellbore and the production wellbore of the same target reservoir.

3. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: The concentration of the tracer in the water containing the tracer is 10-20 ppm; the tracer is ammonium thiocyanate or tritium water.

4. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: The proppant in the proppant-containing fracturing fluid has a proppant mass fraction of 5%-15%; the proppant is quartz sand or ceramsite.

5. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: The preparation method of the hydrophobic modified fluid includes the following steps: surface grafting modification of nanoparticles using a silane coupling agent, and then soaking the modified nanoparticles in a hydrophobic polymer solution with a mass fraction of 2%-5% for 12-36 hours to obtain the hydrophobic modified fluid; the soaking temperature is 30-60℃.

6. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 5, characterized in that: The nanoparticles are any one of silicon dioxide, titanium dioxide, Fe2O3, and aluminum oxide; the hydrophobic polymer is any one of epoxy resin, urea-formaldehyde, polyurethane, phenolic resin, and furfural alcohol; and the silane coupling agent is any one of vinylsilane, aminosilane, methacryloxysilane, and epoxysilane.

7. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: In step S5, when the volume concentration of CO2 in the produced gas reaches 90%, the well is shut off and production is suspended.

8. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: In step S7, production is stopped when the cumulative increase in coalbed methane production of the target coal seam is less than 5%.

9. The integrated method for deep coal seam CO2 fracturing, displacement and production enhancement, and sequestration according to claim 1, characterized in that: The hydrophilic modified fluid is formed by thoroughly stirring silica nanoparticles or alumina nanoparticles in water to form a nanoparticle dispersion with a mass fraction of 5-10%.

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