Fund projects: National 973 Project (2009CB2 19607) and National Major Science and Technology Special Project "Development of Large Oil and Gas Fields and Coalbed Methane" 33, 43 (20 101zx05033-001\, 20/KLOC-)
About the author: Wang Yibing, male, born in June, 1966, received his doctorate from China Geo University (Beijing) in 2008. Senior engineer, engaged in comprehensive research on coalbed methane exploration and development for many years. E-mail:wybmcq69@petrochina.com.cn
(1. Langfang Branch of China Petroleum Exploration and Development Research Institute Langfang 065007; 2. Tianjin 300457, Logging No.2 Company of China Petroleum Bohai Drilling Company)
Based on the analysis of the history and present situation of coalbed methane development in China, it is concluded that since 1980s, coalbed methane development in China has gone through four stages: pre-evaluation, exploration selection, development test and scale development. On the basis of analyzing the geological conditions of coalbed methane in China, it is considered that the discovered coalbed methane fields (enrichment areas) have high general evolution degree and low permeability; This paper summarizes the matching development technologies of coalbed methane suitable for complex geological conditions in China, including drilling and completion technology, reservoir protection technology, hydraulic fracturing technology, drainage and production control technology and so on. The application effects of various technologies are analyzed. It is considered that the development technology of shallow, medium and high rank coalbed methane in China is basically mature. On this basis, the technical development direction of improving the development effect of coalbed methane in China is predicted.
Keywords: CBM development technology fracturing drainage
Development Status and Technical Countermeasures of Coalbed Methane Industry in China
Wang Yibing 1 Yang Jiaosheng 1 Wang Jinyou 2 Zhou Yuangang 2 Bao Qingying 1
(1. Langfang Branch of China Petroleum Exploration and Development Research Institute, Langfang 065007; 2. Second Logging Company of China Petroleum Bohai Drilling Company, Tianjin 300457.
Abstract: Based on the analysis of the history and present situation of coalbed methane development in China, four stages of coalbed methane development since1980s are summarized, namely "pre-evaluation, exploration and regional optimization, development test and scale development". Through the analysis of geological conditions, it is revealed that the discovered coalbed methane fields generally have the characteristics of high evolution degree and low permeability. At the same time, the matching technologies of coalbed methane development suitable for complex geological conditions in China are summarized, including drilling and completion technology, coal seam protection technology, hydraulic fracturing technology and dehydration control technology, and the application effects of each technology are evaluated. Generally speaking, it can be considered that the development technology of medium and high rank coalbed methane shallow than 1000 m is basically mature. Finally, the development direction of the technology is predicted.
Keywords: coalbed methane; Develop technology; Hydraulic fracturing; dehydrate
China is rich in coalbed methane resources. It is predicted that the resource of shallow coalbed methane in 2000m is 36.8 trillion m3 (Ministry of Land and Resources, 2006), and the recoverable resource is about 1 1 trillion m3, which is second only to Russia and Canada, surpassing the United States and ranking third in the world. Large-scale development of abundant domestic coalbed methane resources can reduce China's dependence on imported oil and gas to a certain extent, and at the same time, it is of great significance to realize China's energy strategy succession and sustainable development, reduce coal mine gas content and gas emission, reduce coal mine gas disasters and protect the atmospheric environment.
1 the scale development of coalbed methane has started and the industry has taken shape.
Since the late 1980s, domestic enterprises and scientific research units of petroleum, coal and geological and mineral systems, as well as some foreign companies, have carried out exploration, development and technical tests in more than 30 coal-bearing areas in China, and obtained high-yield gas in Qinshui Basin, Hancheng, Daning-Jixian, Liulin-Xingxian, Huaibei coalfield and Fuxin coalfield in Liaoning Province. By the end of 20 10, the proven geological reserves of coalbed methane in China were 33110 million m3. According to the characteristics of coalbed methane in different coal ranks, we have mastered the techniques of laboratory analysis and geological evaluation, drilling and completion of vertical wells/cluster wells, drilling techniques of multi-branch horizontal wells, air/foam drilling and underbalanced reservoir protection techniques of gas injection and pressure keeping in horizontal wells, and injection/pressure drop well testing techniques. A series of technologies, such as fracturing stimulation and drainage, have obtained stable airflow with economic value in southern Qinshui Basin, eastern margin of Ordos Basin, southern Ningwu Basin, Fuxin Coalfield, Tiefa Coalfield, Huaibei of Huainan and other places, which has prepared reliable resources and technical conditions for large-scale development.
In recent years, with the rapid development of domestic natural gas market and the gradual improvement of natural gas basic pipe network, the development of coalbed methane has ushered in unprecedented opportunities. Especially in 2007, the government issued a subsidy policy for coalbed methane development, which greatly mobilized the enthusiasm of relevant enterprises to invest in coalbed methane industry and promoted the rapid development of coalbed methane industry. In recent years, the number of CBM development wells in China has increased from less than 100 to more than 5,240 (including about 100 horizontal wells). The built CBM production capacity is about 3 billion m3/ year, and the annual gas production exceeds 1 0.50 billion m3 (Figure1), which is expected to be "Twelfth Five-Year Plan".
The development of coalbed methane in China has mainly gone through four stages (Figure 2).
Figure 1 CBM development wells and production figures in China over the years.
Classification of coalbed methane development stages in China.
Pre-evaluation stage in 1980s: Pre-geological evaluation research was carried out in more than 30 coalbed methane target areas in China;
1992~2000 exploration selection stage: drilling coalbed methane wells in Fengcheng, Jiangxi, Lengshuijiang, Liulin, Jincheng, Tangshan, Hebei, Fengfeng, Jiaozuo and Hancheng, Shaanxi, and conducting small well group tests in Liulin, Jincheng and Fuxin;
Development test stage from 2000 to 2005: development pilot tests were carried out in Qinshui, Shanxi, Hancheng, Shaanxi and Fuxin, Liaoning;
From 2006 to now, the scale development stage: the surface development of coalbed methane in Qinshui coalbed methane field, Hancheng block of coalbed methane field in eastern Hubei, Liulin block, Fuxin, Liaoning, Tiefa and other places have initially formed scale and entered the stage of commercial development. Especially in 2007, the state introduced the mining subsidy policy. For every 1 m3 of coalbed methane produced, the state subsidized 0.2 yuan, which greatly mobilized the enthusiasm of production enterprises, increased investment, and the coalbed methane industry entered a stage of rapid development. In 20 10, the national coalbed methane output reached1500 million cubic meters.
2 CBM development technology status
In many years of exploration and development practice, according to the geological characteristics of coalbed methane in China, the matching technologies such as drilling and completion, surface construction and gathering and transportation treatment suitable for China's national conditions have been gradually explored. , a CBM development entity represented by large state-owned coal mining groups such as China Petroleum, Zhonglian CBM and Shanxi Coal Group, a powerful international large-scale energy company, and CBM technical service teams such as drilling and completion, ground construction and compressed transportation have been formed, with a total capacity of 1000m.
The coal and rock properties of coal seams with different evolution degrees are different, mainly in the compaction degree, mechanical strength and adsorption capacity of coal and rock, and their gas content, permeability and wellbore stability are quite different (Wang Yibing et al., 2006). Therefore, coalbed methane resources of different coal ranks need corresponding technical means to be developed. After years of exploration and development, China has initially formed a series of CBM development, drilling, completion, fracturing and drainage technologies.
2. 1 drilling and completion technology
2. 1. 1 Open-hole/cave completion technology of air drilling for coalbed methane exploitation in high permeability area of middle and low rank.
In China, the coal seam permeability in low rank areas is generally greater than 10mD, and the coal seam permeability in high rank areas can also be greater than 5mD. For the exploitation of coalbed methane in this kind of high permeability coal seam, fracturing is generally not needed (the mechanical strength of low rank coal seam is low, and fracturing is easy to form a large number of pulverized coal to block cleavage). Bare screen pipe can be used to complete the coal seam section or cave completion method can be adopted, and caves can be built according to the characteristics that the coal seam is easy to collapse when the stress changes, so as to expand the exposed area of the coal seam and increase the use of air/foam drilling in drilling construction, which can not only improve the penetration rate, but also effectively reduce the pollution of the coal seam.
Open hole cave completion has achieved good results in the development of some coalbed methane fields abroad, such as San Juan Basin and Fenhe Basin in the United States (Zhao Qingbo et al., 1997, 1999), especially in the development of high permeability and overpressure coalbed methane fields.
There are two commonly used wellbore structures:
(1) is a well structure widely used at present, which is suitable for coal reservoirs with good stability without casing after cavity formation.
(2) Run the sieve tube after hole building, which is suitable for reservoirs with poor stability.
This technology has been tested in the eastern margin of Ordos basin, Lengshuijiang River in Hunan and southern Junggar in Xinjiang, and the effect is not ideal, which needs further exploration and improvement.
2. 1.2 Technology of CBM recovery by vertical well fracturing in large well group in medium-high coal rank and medium-permeability area
The permeability of coal seam in the middle and high coal rank permeability area is generally 0.5~5mD, and the single well stimulation effect of casing perforation and sand fracturing is the most obvious. The key technology lies in long-term continuous drainage after fracturing of large well groups, so as to realize desorption and gas production of a large amount of methane gas adsorbed by coal seams after large-area depressurization. This technology is the most widely used and mature in China. Most CBM wells with depths less than 1000 m, such as Hancheng, Sanjiao and Liulin areas in the south of Qinshui Basin, the eastern edge of Ordos, and Liu Jia block in Fuxin coal-bearing area in Liaoning Province, have achieved good results. Most wells have obtained a stable gas flow of 2000~ 10000m3/d, and hundreds of wells have been stable for 5~ 10 years.
2. 1.3 Multi-branch horizontal well mining technology of coalbed methane in low permeability area with medium and high coal rank
This technology is mainly suitable for coal-bearing areas with high mechanical strength and stable shaft wall. By drilling multi-branch wells, the exposed area of coal seam is increased, natural cleavage and fracture are communicated, and the single well production and recovery rate are improved, with remarkable results. Meanwhile, for low permeability (
Multi-branch horizontal well of coalbed methane refers to drilling multiple branch boreholes beside one or two main horizontal boreholes as gas leakage channels. Branch drilling can cross more cleavage fracture systems in coal seam, communicate fracture channels to the maximum extent, increase gas leakage area and gas flow permeability, make more methane gas enter the main channel, and improve gas production of single well. Multi-branch horizontal well integrates drilling, completion and stimulation measures (Wang Yibing et al., 2006), which is one of the main means to develop coalbed methane. This technology has three technical advantages: first, it can increase the single well production, which is about 6~ 10 times of the vertical well production, and at the same time, it can reduce pre-drilling engineering, land occupation, equipment relocation, drilling workload and drilling fluid consumption, and save the management and operation costs of casing and surface pipelines and gas fields, thus improving the comprehensive benefits of development; Secondly, it can speed up gas production and improve oil recovery. It takes 15~20 years to exploit 80% of recoverable reserves by vertical wells, and only 5~8 years to exploit 70%~80% by lateral horizontal wells (Li Wuzhong et al., 2006), which can greatly improve the recovery ratio of coalbed methane; Third, the horizontal drilling of multi-branch horizontal wells does not need casing running and fracturing, which avoids the damage of fracturing to the roof and floor of coal seam and is convenient for subsequent coal mining. It is the best supporting technology for gas production before coal mining.
At present, more than 6,543.8+000 multi-branch horizontal wells have been completed in Qinshui Basin, the eastern edge of Ordos Basin and Ningwu Basin, and the daily output of single well in the south of Qinshui Basin reaches 8,000-55,000m3, with the highest daily output reaching100000 m3, which is 4-654.38+00 times that of the vertical well fracturing method.
2.2 Reservoir protection technology
2.2. 1 coalbed methane air drilling technology
There are mainly air drilling and foam drilling technologies, the main advantages of which are that underbalanced drilling can be realized, coal seam damage is small, ROP is fast, drilling cycle is short, and comprehensive drilling cost is low. However, air/foam drilling also has limitations and is not suitable for any formation. Because air/foam can't carry additives to keep the borehole stable, it can't directly use air to drill through unstable formations. When drilling into the aquifer, cuttings and fine dust will become slugs. Because the liquid appears in the annulus, it will wet the water-sensitive shale, resulting in well collapse and sticking. In addition, wet cuttings will stick together and form a mud cake ring on the outer wall of the drill pipe, which cannot be brought up from the annulus by air. When filling the annulus, the air flow is blocked and the drill pipe is stuck. In addition, when these intermittent air masses move upward along the borehole, they will block the surface equipment and have an unstable impact on the borehole wall. Therefore, the key of air drilling is to keep the wellbore stable.
2.2.2 Underbalanced Protection Technology for Gas Injection and Pressure Keeping in Horizontal Wells
After the main shaft of the multi-branch horizontal well is connected with the karst cave well, during the drilling process of the horizontal well, the tubing is put into the karst cave vertical well, the packer is put into the karst cave vertical well, and then the gas is injected into the karst cave vertical well through the tubing, and the gas is discharged from the annular space of the horizontal well, so as to maintain the annular pressure of the horizontal well and ensure the stability of the borehole wall (Figure 3).
Fig. 3 Schematic diagram of underbalanced drilling profile
The air compressor injects air from the vertical shaft, and the compressed air, coal dust and clean water drilling fluid are fully mixed in the process of high-speed upward movement, forming a three-phase annular flow of gas, liquid and solid. In principle, the returned mixed fluid enters the liquid-gas separator through the side flow port of the rotary head for separation, the mixed fluid flows into the vibrating screen from the liquid outlet, and the pulverized coal mixed with gas enters the combustion pipeline from the gas flow pipeline and is discharged. At the outlet of the combustion pipeline, there is a large-displacement fan to blow away the discharged gas as soon as possible.
If the mixed fluid separated from the three-phase separator is not obvious and the liquid is atomized water droplets, the liquid flow pipeline of the separator is closed, and the pulverized coal and wastewater are collected and treated from the grit port at the bottom of the separator, and the pulverized coal mixed with gas enters the combustion pipeline from the gas pipeline and is discharged. If the separator has limited processing capacity or the combustion pipeline is blocked, the mixture can be discharged urgently by using the throttle pipeline temporarily. In the process of construction, it is required that the ground pipelines are unblocked and all kinds of valves are flexible and reliable.
2.3 CBM well hydraulic fracturing technology
2.3. 1 fracturing fluid according to the characteristics of coal reservoir
Fracturing fluid is the key link of hydraulic fracturing reconstruction of coal seam, and its main function is to open the fracture in the target layer and transport proppant along the fracture. Therefore, it is important to consider the viscosity characteristics of fluid, which not only has high viscosity at the beginning of fracturing, but also has a rapid decline when fracturing fluid returns. However, successful hydraulic fracturing technology also requires other properties of the fluid. Besides having proper viscosity in cracks, it should also have low friction during pumping, which can well control fluid filtration, quickly break the glue, and quickly return after construction, which should be economically feasible.
The basic basis of fracturing fluid selection is: strong adaptability to coalbed methane reservoir, reducing the damage of fracturing fluid to reservoir; Meet the requirements of fracturing technology and achieve as high conductivity as possible to support fractures. According to the characteristics of coalbed methane reservoir at present, the following aspects should be considered in the study of fracturing fluid:
The reservoir temperature is 25~50℃ and the well depth is 300 ~ 1000 m, which belongs to the category of low temperature shallow wells. Therefore, it is required that fracturing fluid is easy to break gel and flow back at low temperature to meet the requirements of low-temperature fracturing fluid system, and friction reduction of fracturing fluid should also be considered. Coalbed methane is a low porosity, low permeability and ultra-low permeability reservoir, which requires fracturing fluid to have good drainage ability and completely break the gel; The clay mineral content of the reservoir is low and its water sensitivity is weak. Hydration expansion is not the main problem of fracturing fluid, but the main problems are low permeability and porosity of reservoir, gel breaking and backflow of fracturing fluid, and reducing the potential secondary damage of fracturing fluid. It is required that the filtrate loss of fracturing fluid is low and the efficiency of fracturing fluid is improved.
In order to meet the construction requirements of large displacement and high sand ratio in coal seam fracturing, fracturing fluid should have good temperature resistance and shear resistance at a certain temperature to meet the requirements of sand carrying in fracturing; At the same time, the efficiency of fracturing fluid is improved and the filtration rate is controlled. Considering the low friction pressure loss, it is required that the fracturing fluid has a proper crosslinking time to ensure the lowest construction pump pressure and large construction displacement as much as possible; Appropriate types of gel breaker and construction scheme are adopted to meet the needs of rapid gel breaking and flowback after fracturing without affecting the sand carrying capacity of fracturing fluid, so as to reduce the damage of fracturing fluid to reservoirs and supporting fractures; It is required that the fracturing fluid has low surface tension and good demulsification performance, which is beneficial to the backflow of fracturing fluid; The fracturing fluid should be operable, simple to use, economical and efficient, safe in construction and in line with environmental protection requirements.
2.3.2 Optimization of coal seam fracturing scheme
Aiming at the fracturing scheme of a block, the general idea of optimization research is: on the basis of analyzing the fracturing geological characteristics of the target block, according to the main geological characteristics of the block, the optimization research of various process parameters is carried out. Firstly, the optimal joint length and conductivity are determined according to the physical characteristics of the target block, and then the construction parameters are determined, including displacement, scale, sand ratio, pre-fluid percentage, etc. A series of supporting technical measures are put forward to optimize the joint length and conductivity and ensure that the supporting section is as optimal as possible.
Optimization of fracturing construction parameters refers to optimizing fracturing construction parameters through 3D fracturing analysis and design software with optimizing fracture length and conductivity as the objective function.
The volume of pad fluid determines how deep the fracture penetration depth can be obtained before the proppant reaches the end. Reasonable pre-liquid volume is the basis of optimal design and the premise of ensuring the success of construction. There are two design goals for the dosage of the preflush: one is to create enough fracture length, and the other is to create enough fractures to ensure that the proppant can enter, and to ensure enough support width to meet the needs of the formation for conductivity.
Displacement optimization is very important for fracturing design. It is found that the variable displacement structure can control the expected crack length and height well. Another important function is to inhibit the occurrence of multiple fractures and reduce near-well friction. The latest literature shows that when the displacement exceeds a certain value, the number of multiple cracks is proportional to the displacement through the response of advanced real-time crack monitoring tools. This technology should be tried, especially for the reservoirs prone to multiple fractures in coal seams.
The optimization of sand adding scale includes the optimization of average sand-liquid ratio and the optimization of sand adding program. The optimization of average sand-liquid ratio is considered from two aspects of construction safety, namely, filtration coefficient and near-hole friction, and draws lessons from construction experience at home and abroad. In the range of possible permeability coefficient of coal seam, the construction risk of average sand ratio of 20%~25% is low. The optimization of sand adding scheme must fully reflect all considerations and technical details in fracturing design and research. The design of sand liquid volume in the first stage is very important. If the initial sand-liquid ratio is too high (or there is an error in the measurement of the sand-liquid ratio of the sand mixer), it may be that the joint width is not enough when sand is added at the beginning, or the initial sand quantity is filtered out too early, resulting in sand plugging in the early or middle and late stage; On the other hand, if the initial sand-liquid ratio is too low and the first batch of proppant is not desalted after the pump is stopped, the fracture may continue to extend after the pump is stopped, which makes the fracture support profile more unreasonable. At the same time, filtering damage will also increase. Therefore, it is very important to start the design of sand-liquid ratio. From the perspective of construction safety, the general practice is to let the first proppant enter the crack and observe it for a period of time. If there is no abnormal pressure, consider increasing the sand-liquid ratio at this stage.
2.4 CBM well drainage technology
Coalbed methane is mainly in adsorption state, and its production mechanism mainly includes three stages: desorption, diffusion and seepage (Zhao Qingbo et al., 200 1). The key problems to be solved in gas production of coalbed methane wells are:
(1) reduce the coal seam pressure to below the critical desorption pressure;
(2) Prevent the pressure of hydraulic fracturing and natural cleavage system of coal seam from dropping too fast or too low, resulting in a sharp drop in permeability;
(3) It takes a long time to reduce blood pressure.
Therefore, coalbed methane gas production engineering should combine different coal and rock characteristics and indoor research work, reasonably determine drainage equipment, control dynamic parameters, give full play to the gas production capacity of coal seam, and control the generation of pulverized coal during drainage to reduce the adverse impact of stress sensitivity of coal reservoir on permeability.
Coal powder migration is a common phenomenon in coalbed methane well mining. In order to reduce the influence of coal powder migration on drainage, the liquid level should be kept slowly and steadily decreasing at the initial stage of drainage, and the sudden rise and fall of liquid level and the excitement of bottom hole pressure should be avoided at the production stage, so as to control the explosion of coal powder, make it produce evenly and keep flowing, and prevent blocking the seepage channel and drainage pipe column of coal seam.
Coal seam has strong plastic deformation ability and strong stress sensitivity, which will cause permeability decline under the condition of strong pumping and strong drainage. In order to promote the efficient drainage of coalbed methane wells (Li et al., 1999), the fluid pressure in the coal seam should be continuously and steadily reduced to avoid the sharp decline of coal seam permeability due to cleavage and fracture closure caused by rapid decline. Different coal seams have different sensitivities, so it is necessary to determine the best liquid falling speed through experiments and simulations. For example, numerical simulation determines that the daily liquid decline rate of Well Jinshi 7 is no more than 30m above the desorption pressure and no more than10m below the desorption pressure; Bottom hole flowing pressure shall not be lower than 1MPa. In general, the daily dropping speed should be controlled within 10m. The closer to the coal seam, the slower the liquid drops. When the liquid level drops to 20~30m above the coal seam, the liquid level will discharge stably, and the depth of the liquid level will be reduced appropriately according to the actual situation after entering the stable gas production stage.
3 development trend of coalbed methane development technology
Compared with the United States, Canada, Australia and other countries with rapid development of coalbed methane industry, China's coalbed methane geological conditions are complex, mainly in the early and multiple coal-forming periods. Most coalfields have experienced multi-stage tectonic movements, and the laws of coalbed methane generation, migration, preservation and accumulation are very complicated. Many years of exploration and development experiments have proved that the distribution of coalbed methane enrichment areas and high permeability areas is very uneven, and the permeability of most coalbed methane enrichment areas is very low, which leads to poor production test results and low exploration success rate in most exploration wells. According to the characteristics of domestic coalbed methane, the research on coalbed methane development technology to improve the efficiency of coalbed methane exploitation in China should include the following directions.
3. 1 geological evaluation technology of high abundance coalbed methane enrichment area
Generally speaking, the prediction of high-abundance coalbed methane enrichment area is based on the joint research of geology, sedimentology, tectonic dynamics, geophysics, groundwater dynamics, geochemistry and other disciplines, combined with seismic processing and interpretation methods, to find coalbed methane enrichment areas suitable for coal seam development, caprock stability, coal-forming period, gas generation period and tectonic movement period. With the improvement of exploration degree and geological understanding in various regions, some development blocks or blocks about to enter development can effectively guide the efficient development of coalbed methane by predicting the high permeability areas where pores and fractures develop in coalbed methane-rich areas through 2D and 3D seismic reservoir inversion and attribute extraction methods, and optimizing the development well pattern and well location deployment.
3.2 Technical Basic Research on Improving Coal Bed Methane Mining Efficiency
Focusing on the formation mechanism and distribution law, coalbed methane reservoir change, fluid phase change, seepage and theoretical correspondence of high-abundance coalbed methane enrichment area, systematic field work, experimental analysis and theoretical research are carried out through joint and interdisciplinary research combining chemical kinetics, seepage mechanics and macro-research and micro-research. Taking the bottom-hole pressure response of coalbed methane as the main research object, the inter-well interference mechanism and development mode optimization of coalbed methane development are studied from both static and dynamic aspects by using multi-well well test technology and numerical simulation technology. Studying the basic theory of reservoir reconstruction suitable for China's geological conditions and improving the efficiency of coalbed methane exploitation will effectively guide the progress of coalbed methane development technology.
3.3 Study on Low-cost and High-efficiency Drilling Technology for Coalbed Methane
Aiming at the coalbed methane resources with the depth of 300 ~1000 m at present, the air drilling technology has been tackled and the vehicle-mounted light air drilling rig has been developed. Through the combination of core experiment, theoretical analysis and production performance analysis, the design method and construction technology of coalbed methane drilling in the past are summarized, and the advanced drilling technologies such as multi-branch horizontal well, U-shaped well, slim hole short radius hydraulic jet drilling and coiled tubing drilling at home and abroad are tracked, the stimulation effect is analyzed, and the applicable technologies are optimized. At the same time, we should also consider the development technology of coalbed methane resources with the depth exceeding1000 m.
3.4 Research on Efficient Transformation Technology of Coal Seam
According to the mechanical experimental data of coal seam and roof and floor and the compatibility of fracturing fluid, the main mechanism of coal seam damage is analyzed, and a new fracturing fluid system suitable for coal seam fracturing under different geological conditions is developed. Combined with the geological characteristics of coal seams in typical coal-bearing basins, the technology suitable for coalbed methane fracturing is explored.
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