•  
  •  
 

Coal Geology & Exploration

Abstract

Objective Deep coalbed methane (CBM) holds considerable resource potential. However, deep CBM reservoirs exhibit high in-situ stresses, while deep coals feature strong plasticity and heterogeneity. These characteristics render it challenging to generate complex fracture networks through conventional fracturing, thus restricting the large-scale commercial development of deep CBM resources. Multi-round fracturing enables fracture initiation, propagation, and propping through sequential cycles of fracturing fluid injection, pump shut-in, and injection. By constantly changing near-wellbore stress fields, this technique facilitates the formation of complex fracture networks and ensures uniform reservoir stimulation. Method Using the finite-discrete element method (FDEM), this study established a numerical model to simulate hydraulic fracture propagation in deep CBM reservoirs. Then, it systematically analyzed the stress evolution patterns and fracture propagation characteristics during multi-round fracturing, assessed the reservoir stimulation performance, and optimized critical fracturing parameters. Last, in combination with post-fracturing analysis of field test wells, the effectiveness of the optimized process was verified, and the mechanisms behind fracture generation during multi-round fracturing were identified. Results and conclusions The results indicate that multi-round fracturing achieves dynamic stress reconstruction through stress interference. Specifically, during pump shut-in, fracturing fluid leakoff results in a drop in the fluid pressure within fractures. This reduces the stress shadow effect between adjacent fractures while also decreasing the maximum and minimum horizontal principal stresses in the near-wellbore zone, as well as the differences between the stresses. Consequently, the stress redistribution effectively mitigates competition among fracture clusters, driving previously suppressed fractures between dominant fractures to reinitiate and propagate synergistically. The optimized multi-round fracturing was applied to deep CBM wells in the Linxing-Shenfu block of the Ordos Basin. Field test results indicate that the optimized multi-round fracturing increased the stimulated reservoir volume (SRV) by 49% and cumulative gas production by 165% relative to conventional fracturing. Comparison between multiple fracturing stages of the same well further demonstrates that multi-round fracturing significantly outperformed conventional fracturing in both fracture uniformity and average fracture length. In addition, wells subjected to multi-round fracturing generally exhibited higher gas production than conventionally fractured wells. Overall, the results of this study are expected to provide a scientific basis for the efficient stimulation of deep CBM reservoirs.

Keywords

deep coalbed methane (CBM), multi-round fracturing, finite-discrete element method (FDEM), numerical simulation, stress reconstruction, uniform stimulation, complex fracture network

DOI

10.12363/issn.1001-1986.26.05.0271

Reference

[1] 汪海阁,夏焱,丁吉平,等. 中石油深层煤岩气钻完井工程技术现状及展望[J]. 石油学报,2025,46(8):1576−1588. WANG Haige,XIA Yan,DING Jiping,et al. Current status and prospect of CNPC's deep coal–rock gas drilling and completion engineering technologies[J]. Acta Petrolei Sinica,2025,46(8):1576−1588.

[2] 匡立春. 煤岩气的地质内涵、工程实践与发展战略综述[J]. 世界石油工业,2026,33(1/2):75−88. KUANG Lichun. Review of the geological connotation,engineering practices,and development strategies of coalstone gas[J]. World Petroleum Industry,2026,33(1/2):75−88.

[3] 国家能源局石油天然气司,国家油气战略研究中心,中国石油勘探开发研究院,等. 中国油气勘探开发发展报告2025[R]. 北京: 国家能源局, 2025.

[4] 吴裕根,门相勇,娄钰. 我国"十四五"煤层气勘探开发新进展与前景展望[J]. 中国石油勘探,2024,29(1):1−13. WU Yugen,MEN Xiangyong,LOU Yu. New progress and prospect of coalbed methane exploration and development in China during the 14th Five–Year Plan period[J]. China Petroleum Exploration,2024,29(1):1−13.

[5] 周立宏,熊先钺,李勇,等. 深层煤层(岩)气革命性突破及关键理论与技术[J]. 天然气工业,2025,45(5):17−30. ZHOU Lihong,XIONG Xianyue,LI Yong,et al. Revolutionary breakthroughs and key theories and technologies in deep coalbed methane development[J]. Natural Gas Industry,2025,45(5):17−30.

[6] 陶树,张守仁,毕彩芹,等. 中国"十四五"时期深部煤层气勘探开发新进展与前景展望[J]. 煤炭学报,2026,51(2):1440−1462. TAO Shu,ZHANG Shouren,BI Caiqin,et al. Advances and prospects in deep coalbed methane exploration and development in China during the "14th Five–Year Plan" period[J]. Journal of China Coal Society,2026,51(2):1440−1462.

[7] 霍超,郭海晓,王蕾,等. 双碳背景下中国深部煤层气勘探开发研究进展[J]. 科学技术与工程,2025,25(14):5705−5720. HUO Chao,GUO Haixiao,WANG Lei,et al. Research progress of deep coalbed methane exploration and development in China under the dual carbon background[J]. Science Technology and Engineering,2025,25(14):5705−5720.

[8] 李国欣,陈瑞银,温志新,等. 全球煤岩气资源潜力与分布[J]. 石油勘探与开发,2026,53(1):14−26. LI Guoxin,CHEN Ruiyin,WEN Zhixin,et al. Global coal–rock gas resource potential and distribution[J]. Petroleum Exploration and Development,2026,53(1):14−26.

[9] JOHNSON R. Successful implementation of two decades of Australian coal seam gas research can improve low–permeability coal productivity and recovery[C]//SPE/AAPG/SEG Unconventional Resources Technology Conference. Houston: American Association of Petroleum Geologists,2024: URTEC–4025119–MS.

[10] JOHNSON R L,SALDUNGARAY P. The first application of MPs in two deep,low–permeability,Permian coal stimulations in the Taroom Trough,Bowen Basin,Australia[C]//Unconventional Resources Technology Conference. Houston: American Association of Petroleum Geologists,2025: 591−607.

[11] SAMPATH K H S M,PERERA M S A,ELSWORTH D,et al. Effect of coal maturity on CO2–based hydraulic fracturing process in coal seam gas reservoirs[J]. Fuel,2019,236:179−189.

[12] 王希栋,段利江,张松航,等. 北美深部煤层气勘探进展与前景展望[J/OL]. 煤炭科学技术,2026:1−17 [2026-04-15]. https://link.cnki.net/urlid/11.2402.TD.20260414.1731.009. WANG Xidong,DUAN Lijiang,ZHANG Songhang,et al. Exploration progress and prospects of deep coalbed methane in North America[J/OL]. Coal Science and Technology,2026:1−17 [2026-04-15]. https://link.cnki.net/urlid/11.2402.TD.20260414.1731.009.

[13] 杨帆,李斌,王昆剑,等. 深部煤层气水平井大规模极限体积压裂技术:以鄂尔多斯盆地东缘临兴区块为例[J]. 石油勘探与开发,2024,51(2):389−398. YANG Fan,LI Bin,WANG Kunjian,et al. Extreme massive hydraulic fracturing in deep coalbed methane horizontal wells: A case study of the Linxing Block,eastern Ordos Basin,NW China[J]. Petroleum Exploration and Development,2024,51(2):389−398.

[14] 陈贞龙,王运海,刘晓,等. 延川南深部煤层气开发关键技术与地质工程一体化实践[J]. 煤田地质与勘探,2025,53(1):142−151. CHEN Zhenlong,WANG Yunhai,LIU Xiao,et al. Critical technologies and geology–engineering integration practices for deep CBM production in the Yanchuannan CBM field[J]. Coal Geology & Exploration,2025,53(1):142−151.

[15] 魏伟. 煤层气多轮次压裂工艺研究与应用[J]. 中国石油和化工标准与质量,2022,42(1):190−192.

[16] 李小刚,唐政,朱静怡,等. 深层煤岩气压裂研究进展与展望[J]. 天然气工业,2024,44(10):126−139. LI Xiaogang,TANG Zheng,ZHU Jingyi,et al. Research progress and prospect of deep coalrock fracturing[J]. Natural Gas Industry,2024,44(10):126−139.

[17] 熊先钺,甄怀宾,李曙光,等. 大宁–吉县区块深部煤层气多轮次转向压裂技术及应用[J]. 煤田地质与勘探,2024,52(2):147−160. XIONG Xianyue,ZHEN Huaibin,LI Shuguang,et al. Multi–round diverting fracturing technology and its application in deep coalbed methane in the Daning–Jixian Block[J]. Coal Geology & Exploration,2024,52(2):147−160.

[18] 闫涛滔,邓志宇,吴鹏,等. 鄂尔多斯盆地东缘临兴东区杨家坡区块煤层气井产能特征及主控因素[J]. 现代地质,2024,38(6):1545−1556. YAN Taotao,DENG Zhiyu,WU Peng,et al. Characteristics and key control factors of coalbed methane well productivity in the Yangjiapo Block,eastern Linxing district,Ordos Basin[J]. Geoscience,2024,38(6):1545−1556.

[19] LISJAK A,MAHABADI O K,HE L,et al. Acceleration of a 2D/3D finite–discrete element code for geomechanical simulations using General Purpose GPU computing[J]. Computers and Geotechnics,2018,100:84−96.

[20] 刘建忠,朱光辉,刘彦成,等. 鄂尔多斯盆地东缘深部煤层气勘探突破及未来面临的挑战与对策:以临兴–神府区块为例[J]. 石油学报,2023,44(11):1827−1839. LIU Jianzhong,ZHU Guanghui,LIU Yancheng,et al. Breakthrough,future challenges and countermeasures of deep coalbed methane in the eastern margin of Ordos Basin: A case study of Linxing–Shenfu Block[J]. Acta Petrolei Sinica,2023,44(11):1827−1839.

[21] MUNJIZA A,OWEN D R J,BICANIC N. A combined finite–discrete element method in transient dynamics of fracturing solids[J]. Engineering Computations,1995,12(2):145−174.

[22] 齐洪岩,王振林,郑国庆,等. 页岩油储集层水平井密切割压裂裂缝非均衡扩展机理[J]. 新疆石油地质,2025,46(6):734−741. QI Hongyan,WANG Zhenlin,ZHENG Guoqing,et al. Unbalanced fracture propagation mechanism during horizontal well intensive fracturing in shale oil reservoirs[J]. Xinjiang Petroleum Geology,2025,46(6):734−741.

[23] IDA Y. Cohesive force across the tip of a longitudinal–shear crack and Griffith's specific surface energy[J]. Journal of Geophysical Research,1972,77(20):3796−3805.

[24] MAHABADI O K,LISJAK A,MUNJIZA A,et al. Y–geo: New combined finite–discrete element numerical code for geomechanical applications[J]. International Journal of Geomechanics,2012,12(6):676−688.

[25] TATONE B S A,GRASSELLI G. A calibration procedure for two–dimensional laboratory–scale hybrid finite–discrete element simulations[J]. International Journal of Rock Mechanics and Mining Sciences,2015,75:56−72.

[26] MUNJIZA A,ANDREWS K R F,WHITE J K. Combined single and smeared crack model in combined finite–discrete element analysis[J]. International Journal for Numerical Methods in Engineering,1999,44(1):41−57.

[27] MUNJIZA A. The combined finite–discrete element method[M]. Hoboken: Wiley, 2004.

[28] WITHERSPOON P A,WANG J S Y,IWAI K,et al. Validity of Cubic Law for fluid flow in a deformable rock fracture[J]. Water Resources Research,1980,16(6):1016−1024.

[29] 范志利,石军太,王春琦,等. 鄂尔多斯盆地临兴–神府区块深部煤层渗透率应力敏感和速敏实验研究[J]. 中国石油勘探,2025,30(4):141−159. FAN Zhili,SHI Juntai,WANG Chunqi,et al. Experimental study of permeability stress sensitivity and velocity sensitivity of deep coal seams in Linxing–Shenfu Block,Ordos Basin[J]. China Petroleum Exploration,2025,30(4):141−159.

[30] 米洪刚,吴见,彭文春,等. 神府区块深部煤储层力学特性及裂缝扩展机制[J]. 煤田地质与勘探,2024,52(8):32−43. MI Honggang,WU Jian,PENG Wenchun,et al. Mechanical characteristics and fracture propagation mechanism of deep coal reservoirs in the Shenfu Block[J]. Coal Geology & Exploration,2024,52(8):32−43.

[31] 彭文春,米洪刚,徐立富,等. 神府区块深部煤储层可压性评价方法及应用[J]. 煤炭科学技术,2025,53(3):238−247. PENG Wenchun,MI Honggang,XU Lifu,et al. Fracability evaluation and classification of deep coal reservoirs in the Shenfu Block[J]. Coal Science and Technology,2025,53(3):238−247.

[32] YANG Ruiyue,GONG Yanjin,SHI Weiyi,et al. Oriented perforation strategies for hydraulic fracturing in deep coalbed methane horizontal wells[J]. SPE Journal,2026,31(4):2467−2488.

[33] 何青琴,杨永全,何世明,等. 低渗透油气田重复压裂诱导应力场模拟研究[J]. 天然气技术,2010,4(1):30−32. HE Qingqin,YANG Yongquan,HE Shiming,et al. Refracturing–induced stress field simulation of low–permeability oil and gasfields[J]. Natural Gas Technology,2010,4(1):30−32.

[34] 郎皞. 注采井组重复压裂前应力演化机理研究[D]. 北京: 中国石油大学(北京), 2022. LANG Hao. An investigation on the evolution of in–situ stress before refracturing in the injection–production well group[D]. Beijing: China University of Petroleum (Beijing), 2022.

[35] CHEN Xuexi,LIU Zijian,LI Tao,et al. Microstructural evolution and damage mechanism of water–immersed coal based on physicochemical effects of inorganic minerals[J]. Materials,2024,17(22):5579.

Download Chinese Version

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.