Method for fracturing deep coal bed gas

Abstract

The invention belongs to the technical field of deep coal-bed gas, and relates to a method for fracturing deep coal-bed gas, which comprises the following steps of: determining reserves and distribution conditions of coal-bed gas according to stratum data of the deep coal-bed gas; according to the reserves and distribution conditions of the coal bed gas, well drilling is conducted to reach a target stratum; ultrasonic fracturing is conducted on the target stratum, so that the target stratum vibrates directionally, and micro-cracks are generated; and high-pressure water jet is injected into the micro-crack to enlarge the width of the micro-crack, so that an effective communicating hole channel between the coal seam and the shaft is enlarged. According to the method, the development efficiency of the deep coal bed gas can be effectively improved, the gas recovery efficiency can be improved, and meanwhile the safety and sustainability of the development process of the deep coal bed gas are guaranteed.

Description

Technical Field

[0001] The invention relates to a method for deep coalbed methane fracturing, belonging to the technical field of deep coalbed methane. Background Art

[0002] Coalbed methane (CBM) is an unconventional natural gas that is self-generated and self-stored during the coal-forming process within coal-bearing rock formations, primarily from humic organic matter. Its primary component is CH4, which accounts for over 90%. CBM is generated within coal seams and stored in both adsorbed and free states within the coal seams and adjacent rock formations. Extracting CBM requires establishing an effective communication channel between the coal seam and the wellbore, and the most effective method for creating this channel is hydraulic fracturing of the coal seam. Fracturing CBM wells differs significantly from fracturing oil and gas wells in terms of technology: coal seams have a well-developed cleat system, resulting in significant filtration losses and difficulty in forming long fractures; coal seams are susceptible to adsorption and damage, making reservoir protection challenging. Consequently, CBM fracturing is challenging.

[0003] In addition, coal seams that are usually more than 1,500 meters deep are called deep seams. Because deep coal seams are characterized by high pressure, high temperature, and low permeability, traditional fracturing technology may be inapplicable or inefficient. Deep coalbed methane reservoirs are usually in a high ground stress environment, and the coal body structure is tight, the degree of natural fracture development is low, which increases the difficulty of fracturing. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for deep coalbed methane fracturing, which can effectively improve the development efficiency of deep coalbed methane and ensure the safety and sustainability of the deep coalbed methane development process.

[0005] To achieve the above-mentioned objectives, the present invention proposes the following technical solutions: a method for deep coalbed methane fracturing, comprising the following steps: determining the reserves and distribution of coalbed methane through formation data of deep coalbed methane; drilling to reach the target formation based on the reserves and distribution of the coalbed methane; performing ultrasonic fracturing on the target formation to cause the target formation to vibrate in a direction to generate microcracks; and injecting a high-pressure water jet into the microcracks to expand the width of the microcracks, thereby expanding the effective communication channel between the coal seam and the wellbore.

[0006] Furthermore, stratigraphic data of deep coalbed methane is obtained through geological exploration; electromagnetic exploration or three-dimensional seismic exploration is introduced into the geological exploration to obtain geological exploration data, and the geological exploration data is input into a deep learning algorithm model to process and interpret it to obtain the stratigraphic data of deep coalbed methane.

[0007] Furthermore, the formation data of deep coalbed methane includes physical properties, rock type, rock structure and rock composition of the formation.

[0008] Furthermore, by evaluating the formation data of the deep coalbed methane, an evaluation result is generated; the reserves and distribution of the coalbed methane are determined based on the evaluation result and the geological exploration data; and the target formation and the corresponding fracturing plan are selected based on the determined reserves and distribution of the coalbed methane.

[0009] Furthermore, the method for implementing ultrasonic fracturing on the target formation is: installing ultrasonic equipment at the wellhead of the target formation, starting the ultrasonic equipment, optimizing the frequency and power parameters of the emitted ultrasonic waves according to the characteristics of the target formation, and emitting the optimized ultrasonic waves to the target formation to cause the target formation to vibrate in a direction, thereby generating microcracks in the target formation.

[0010] Furthermore, the ultrasonic equipment includes an ultrasonic generator and an ultrasonic sensor. The ultrasonic generator is used to emit ultrasonic waves. When the ultrasonic waves propagate in the coal seam, they encounter the microcracks and generate echo signals. The ultrasonic sensor is used to collect the echo signals, analyze the time delay, amplitude and waveform changes of the echo signals, and infer the location and expansion of the microcracks through the reflection intensity and echo characteristics of the echo signals.

[0011] Furthermore, the echo signals collected by the ultrasonic sensor are collected in real time, the echo signals are interpreted through time domain analysis or Fourier transform, the position and expansion of the microcracks are extracted, the position and expansion of the microcracks are integrated with the downhole parameters and formation conditions, and the integrated data is input into a deep learning algorithm model, so as to perform in-depth analysis of the echo signals and obtain the accurate position and expansion of the microcracks.

[0012] Furthermore, the operating frequency of the ultrasonic generator is 20kHz to 1MHz; when stronger energy needs to be applied to a certain point, a higher frequency ultrasonic generator is selected; if ultrasonic vibration is required in a large range, a lower frequency ultrasonic generator is selected.

[0013] Furthermore, the length of the microcracks is 20-30 cm.

[0014] Furthermore, the high-pressure water jet is used to add fracturing proppant. In the early stage of micro-cracks, fine-grained fracturing proppant is first added to the well to treat the natural cleats to reduce filtration loss; in the middle stage of micro-cracks, medium-grained fracturing proppant is added, and in the late stage of micro-cracks, coarse-grained fracturing proppant is added. The displacement of the high-pressure water jet is 8-15m 3 / min.

[0015] The technical solution of the present invention has at least the following technical effects or advantages: 1. The present invention can effectively improve the development efficiency of deep coalbed methane and also increase the gas recovery rate, while ensuring the safety and sustainability of the deep coalbed methane development process.

[0016] 2. The present invention combines ultrasonic fracturing and hydraulic fracturing to improve the permeability of coalbed methane and enhance gas extraction efficiency.

[0017] 3. Ultrasonic fracturing makes it easier for gas to be released from coal seams, thereby improving gas extraction efficiency and reducing extraction costs. At the same time, ultrasonic waves can also reduce residual stress inside the coal seams, expand microcracks in the coal seams, and thus promote gas flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a flow chart of a method for deep coalbed methane fracturing in one embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms used are for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In order to solve the problems existing in the prior art, such as the inapplicability or low efficiency of traditional fracturing technology, and the fact that deep coalbed methane reservoirs are usually in a high ground stress environment, with a tight coal body structure and a low degree of natural fracture development, the present invention proposes a method for deep coalbed methane fracturing, which carries out drilling work according to the distribution of coalbed methane in the formation, and then implements ultrasonic fracturing on the target formation, using ultrasonic energy to directionally vibrate the target formation to generate microcracks and improve the permeability of coalbed methane; the width of the microcracks is expanded by injecting high-pressure water jets into the microcracks, and the coal seam is fractured by high-pressure water jets to improve the production capacity of coalbed methane. The scheme of the present invention is described in detail below with reference to the accompanying drawings and through examples.

[0021] Example 1 The present invention discloses a method for deep coalbed methane fracturing, such as Figure 1 As shown, this embodiment is described by taking the coal reservoir in the Ordos Basin as an example, and includes the following steps: S1 determines the reserves and distribution of coalbed methane through deep coalbed methane formation data.

[0022] Special logging methods, such as electromagnetic exploration or 3D seismic exploration, are introduced. For example, nuclear magnetic resonance (NMR) logging measures the free precession of hydrogen nuclei in the geomagnetic field. Polarization coils in downhole instruments generate a strong pulsed magnetic field perpendicular to the geomagnetic field, forcing the spin axes of the hydrogen nuclei to deviate from the direction of the geomagnetic field. After the polarization field is removed, the hydrogen nuclei precess around the geomagnetic field and gradually return to their original state. This precession generates a gradually decaying radio frequency signal in the induction coil. The signal amplitude depends on the number of hydrogen nuclei in the free fluid in the formation, known as the free fluid index. The free fluid index can be used to determine the free fluid porosity of the rock, which, combined with other data, can be used to calculate permeability. Further measuring the thermal relaxation time allows the distinction between oil and water. Electromagnetic exploration provides information such as resistivity of the subsurface formation, while NMR logging provides information such as porosity and the free fluid index. By combining these data, more accurate lithology can be determined. 3D seismic exploration can provide macroscopic information about subsurface structures, such as the distribution and morphology of faults and folds. Nuclear magnetic resonance logging focuses on describing the microscopic characteristics of the reservoir, such as pore structure and fluid properties. Combining the two enables in-depth analysis of reservoir characteristics based on an understanding of the macroscopic structural background. Special logging methods and electromagnetic exploration can provide a deeper understanding of reservoir characteristics. Exploration of deep coalbed methane corresponding strata obtains geological exploration data. Geological exploration data mainly includes topography, geological structure, changes in gravity field, the content and distribution patterns of various elements in rocks, and logging data to fully understand the geological conditions of the entire block (lithology, oil and gas, etc.). Geological exploration data includes data on geological structure, geophysics, geochemistry, drilling, etc., involving a comprehensive study of the entire geological body, while stratigraphic data mainly focuses on the characteristics of the stratum, with an emphasis on describing and dividing different stratigraphic units to establish the temporal and spatial distribution patterns of the stratum.

[0023] The geological exploration data is input into the deep learning algorithm model for processing and interpretation to obtain the stratigraphic data of deep coalbed methane. In this embodiment, the stratigraphic data of deep coalbed methane mainly consists of the physical properties, rock type, rock structure and rock composition of the formation.

[0024] In the above process, deep coalbed methane formation data is evaluated to generate evaluation results. Based on previous research and the collection of data on target block formation thickness, gas content, and reservoir properties, the deep coalbed reservoir conditions are evaluated and graded to guide the selection of subsequent sub-strata for development. Based on the evaluation results and geological exploration data, the reserves and distribution of coalbed methane are determined. Based on these determined reserves and distribution, the target formation and corresponding fracturing scheme are selected. In this example, ultrasonic fracturing and hydraulic fracturing are combined to improve coalbed methane permeability and enhance gas extraction efficiency.

[0025] S2 drills wells to reach the target formation based on the reserves and distribution of coalbed methane.

[0026] S3 performs ultrasonic fracturing on the target formation to cause the target formation to vibrate directionally to generate micro cracks.

[0027] The method for ultrasonic fracturing a target formation involves installing ultrasonic equipment at the wellhead of the target formation, activating the equipment, and optimizing the frequency and power of the transmitted ultrasound waves based on the characteristics of the target formation. The optimized ultrasound waves are then transmitted into the target formation, causing it to vibrate directionally. Before fracturing, the cracks are closed and have a limited width. After fracturing, the cracks open, creating tiny fractures in the target formation, forming microcracks with a width of approximately 2-8 mm.

[0028] In this embodiment, the ultrasonic equipment includes an ultrasonic generator and an ultrasonic sensor. The ultrasonic generator is used to emit ultrasonic waves. When the ultrasonic waves propagate through the coal seam, they encounter microcracks and generate echo signals. The ultrasonic sensor is used to collect the echo signals, analyze the time delay, amplitude, and waveform changes of the echo signals, and infer the location and extension of the microcracks based on the reflection intensity and echo characteristics of the echo signals. An ultrasonic generator suitable for coalbed methane development is selected. In this embodiment, the ultrasonic generator typically operates at a frequency between 20 kHz and 1 MHz. The appropriate frequency is selected based on specific formation conditions. When stronger energy needs to be applied to a specific point, a higher-frequency ultrasonic generator is selected. Higher frequencies are in the MHz band. This means that higher-frequency ultrasonic generators have greater energy concentration and can generate stronger, concentrated energy within a smaller area. When ultrasonic vibrations are required over a larger area, a lower-frequency ultrasonic generator is selected. Higher frequencies are in the kHz band. This means that lower-frequency ultrasonic generators generate ultrasonic waves with a longer propagation distance and a wider range, but with relatively lower applied energy.

[0029] The microcracks generated in this step can improve the permeability of coalbed methane, and the length of the microcracks generated is in the range of 20-30 cm.

[0030] By comparing data before and after fracturing, and considering the influence of coal seam characteristics, ultrasonic parameters, and external factors, field testing and evaluation revealed changes in permeability before and after ultrasonic fracturing. This change in permeability indicates that ultrasonic fracturing facilitates the release of gas from the coal seam, improving gas extraction efficiency and reducing extraction costs. Furthermore, ultrasonic waves can reduce residual stress within the coal seam, expanding microcracks within the coal seam and promoting gas flow.

[0031] After microcracks are generated, monitoring equipment is arranged at the location where the microcracks are generated to detect the expansion of the microcracks in real time. The data of the monitoring equipment is integrated and input into the artificial intelligence analysis and processing model to realize early warning of downhole parameters and intelligent decision-making of operation plans. Specifically, an ultrasonic generator is placed outside the area to be detected to emit ultrasonic pulses. When the sound wave propagates in the coal seam, it will generate echoes when it encounters the generated microcracks. The generated echoes are captured by the ultrasonic sensor. The echo signals collected by the ultrasonic sensor are collected in real time, and the echo signals are interpreted through time domain analysis or Fourier transform to analyze the time delay, amplitude and waveform changes of the echo signals. Then, the position and expansion of the microcracks are extracted through the reflection intensity and echo characteristics of the signal. The position and expansion of the microcracks are integrated with the downhole parameters and formation conditions, and the integrated data are input into the deep learning algorithm model, so as to perform in-depth analysis on the echo signals and obtain the accurate position and expansion of the microcracks. Ultrasonic sensors can monitor the generation and expansion of microcracks in real time, detecting information such as their location, size, and morphology. These sensors transmit this data to a monitoring system for analysis, identifying their expansion and enabling real-time monitoring of changes in the microcrack status of coal seams. This monitoring system can monitor downhole parameters and formation conditions in real time, including key data such as temperature, pressure, and gas composition. Through integrated data processing, operators can promptly understand changes in the formation, helping to reduce risks and ensure safety and control during the development process.

[0032] In this embodiment, the ultrasonic fracturing equipment is an ultrasonic directional fracturing system with a specification model of ZX-UDP-2000.

[0033] S4 injects high-pressure water jets into micro-cracks to expand the width of the micro-cracks, thereby expanding the effective communication channels between the coal seam and the wellbore.

[0034] In this embodiment, the hydraulic fracturing equipment is the JMT-5 ultra-high pressure and high flow rate fracturing equipment. The hydraulic fracturing equipment is used to inject high pressure water jets into the micro cracks, and fracturing proppant is added to the high pressure water jets to expand the width of the micro cracks. In this embodiment, the displacement of the high pressure water jets used is 8~15m 3 / min, preferably 10m 3 The amount of fracturing proppant added is 5% of the total volume of the high-pressure water jet, depending on the specific construction requirements. Hydraulic fracturing can increase the number and size of micro-cracks, thereby improving the permeability and recovery rate of coalbed methane.

[0035] Quartz sand is used as fracturing proppant. In view of the fact that coalbed methane reservoirs are prone to filtration loss, fracturing proppant is added by high-pressure water jet. In the early stage of micro-cracks, fine-grained fracturing proppant is added to the well to treat the natural cleats to reduce filtration loss; medium-grained fracturing proppant is added in the middle stage of micro-cracks, and coarse-grained fracturing proppant is added in the late stage of micro-cracks to fill the edge of the wellbore and artificially form a high-permeability zone to ensure the smooth flow of coalbed methane channels.

[0036] In this embodiment, the particle size of the low-particle-size fracturing proppant is 0.15-0.30 mm; the particle size of the medium-particle-size fracturing proppant is 0.425-0.85 mm; and the particle size of the high-particle-size fracturing proppant is 0.90-1.20 mm.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be included within the scope of protection of the claims of the present invention. The above content is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art who can easily think of changes or replacements within the technical scope disclosed by the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for deep coalbed methane fracturing, characterized in that: The following steps are involved: Determine the reserves and distribution of coalbed methane through deep coalbed methane formation data; Drilling to reach the target formation based on the reserves and distribution of the coalbed methane; Performing ultrasonic fracturing on the target formation to cause the target formation to vibrate directionally to generate microcracks; A high-pressure water jet is injected into the micro-cracks to expand the width of the micro-cracks, thereby expanding the effective communication channel between the coal seam and the wellbore.

2. The method for deep coalbed methane fracturing according to claim 1, characterized in that: The stratigraphic data of deep coalbed methane is obtained through geological exploration; electromagnetic exploration or three-dimensional seismic exploration is introduced into the geological exploration to obtain geological exploration data, and the geological exploration data is input into a deep learning algorithm model to process and interpret it to obtain the stratigraphic data of the deep coalbed methane.

3. The method for deep coalbed methane fracturing according to claim 2, characterized in that: The deep coalbed methane formation data includes physical properties, rock types, rock structures and rock compositions of the formation.

4. The method for deep coalbed methane fracturing according to claim 2, characterized in that: An evaluation result is generated by evaluating the formation data of the deep coalbed methane; the reserves and distribution of the coalbed methane are determined based on the evaluation result and the geological exploration data; and a target formation and a corresponding fracturing plan are selected based on the determined reserves and distribution of the coalbed methane.

5. The method for deep coalbed methane fracturing according to claim 1, characterized in that: The method for implementing ultrasonic fracturing on the target formation is: installing ultrasonic equipment at the wellhead of the target formation, starting the ultrasonic equipment, optimizing the frequency and power parameters of the emitted ultrasonic waves according to the characteristics of the target formation, and emitting the optimized ultrasonic waves to the target formation to cause the target formation to vibrate directionally, thereby generating microcracks in the target formation.

6. The method for deep coalbed methane fracturing according to claim 5, characterized in that: The ultrasonic equipment includes an ultrasonic generator and an ultrasonic sensor. The ultrasonic generator is used to emit ultrasonic waves. When the ultrasonic waves propagate in the coal seam, they encounter the microcracks and generate echo signals. The ultrasonic sensor is used to collect the echo signals, analyze the time delay, amplitude and waveform changes of the echo signals, and infer the location and expansion of the microcracks through the reflection intensity and echo characteristics of the echo signals.

7. The method for deep coalbed methane fracturing according to claim 6, characterized in that: The echo signals collected by the ultrasonic sensor are collected in real time, the echo signals are interpreted through time domain analysis or Fourier transform, the position and extension of the microcracks are extracted, the position and extension of the microcracks are integrated with downhole parameters and formation conditions, and the integrated data are input into a deep learning algorithm model, thereby performing in-depth analysis of the echo signals to obtain the accurate position and extension of the microcracks.

8. The method for deep coalbed methane fracturing according to claim 6, characterized in that: The operating frequency of the ultrasonic generator is 20kHz to 1MHz. When stronger energy needs to be applied to a certain point, a higher frequency ultrasonic generator is selected. If ultrasonic vibration is required in a large range, a lower frequency ultrasonic generator is selected.

9. The method for deep coalbed methane fracturing according to any one of claims 5 to 8, characterized in that: The length of the microcracks is 20-30 cm.

10. The method for deep coalbed methane fracturing according to any one of claims 5 to 8, characterized in that: The high-pressure water jet adds fracturing proppant, and before the micro-cracks are generated, fine-grained fracturing proppant is added to the well to treat the natural cleats to reduce fluid loss; In the middle stage of micro-cracks, medium-sized fracturing proppant is added, and in the late stage of micro-cracks, coarse-sized fracturing proppant is added. The displacement of the high-pressure water jet is 8-15m 3 / min.

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