Coupling mechanisms of fracture propagation and proppant transport indeep coalbed methane reservoirs

Authors

GUO Xiaodong, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, ChinaFollow
ZHANG Shicheng, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China
ZHANG Jingchen, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, ChinaFollow
ZHOU Changjing, Changqing Oilfield Company, PetroChina, Xi’an 710021, China
ZHANG Chengsheng, Petroleum Engineering Field (Pilot Test) Laboratory, Baijiantan District (Karamay High-tech Zone), Karamay 834099, China
QIU Shixin, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China
XI Xiangrui, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China

Abstract

Objectives and Methods Deep coalbed methane (CBM) reservoirs commonly exhibit well-developed beddings, strong mechanical heterogeneity, and high in-situ stress gradients. These characteristics result in pronounced nonlinear fracture propagation and strong multi-field coupling effects during hydraulic fracturing. Consequently, it is challenging to accurately describe the mechanisms governing fracture complexity in deep coal reservoirs using conventional mechanical models for fractures. Using a super-large true triaxial system with dimensions of 2.0 m × 2.0 m × 1.0 m, this study conducted physical simulation experiments on hydraulic fracturing under varying injection rates and viscosities of fracturing fluids. In combination with fracture mechanics and energy conservation theory, this study established an energy balance equation for fracture propagation, a convection-diffusion equation for proppant transport and settling, and a model for the coupling relationships among fracture complexity and the injection rate and viscosity of fracturing fluids. Accordingly, both the dynamic mechanisms behind fracture evolution and the pattern governing the fracture network complexity were systematically elucidated.Results The results indicate that fracture propagation is jointly controlled by the in-situ stress field, fluid pressure field, and bedding structures, representing a unsteady energy conversion process. The fracture propagation rate exhibits a power-law relationship with the energy release rate. The injection rate of fracturing fluids primarily determines the energy input rate and fracture propagation velocity. A high injection rate results in energy concentration in the front of the primary fracture, promoting fracture interconnectivity while suppressing branch development. Accordingly, fracture complexity is reduced. In contrast, a low injection rate corresponds to a more uniform energy distribution, enhancing the accumulation and lateral diffusion of energy. This facilitates multi-point initial cracking and fracture branching, increasing fracture complexity by approximately 25%–35%. Fracturing fluid viscosity significantly influences the energy transfer between fluids and solids, as well as proppant settling behavior. A high viscosity (45 mPa·s) is associated with a significant decrease in the proppant settling velocity. Compared to a low viscosity of 15 mPa·s, the high viscosity increases the proppant transport capacity by approximately 40%, promoting more uniform proppant placement in far-wellbore zones and creating favorable conditions for the formation of continuous hydraulically conductive pathways.Conclusions Empirical relationships derived from experiments and fitting indicate that the fracture complexity exhibits power-law coupling relationships with the injection rate and viscosity of fracturing fluids. Notably, the low-injection-rate and high-viscosity combination is more favorable for the development of 3D fracture networks, with a fractal dimension reaching up to 1.46. The proposed theoretical-experimental coupling framework reveals the energy transfer mechanisms governing fracture propagation and proppant transport in deep coal reservoirs, providing a quantitative theoretical basis for optimizing hydraulic fracturing parameters and predicting fracture complexity in deep unconventional reservoirs.

Keywords

deep coalbed methane (CBM), fracture propagation, proppant placement, true triaxial system, hydraulic fracturing

DOI

10.12363/issn.1001-1986.25.10.0793

Recommended Citation

GUO Xiaodong, ZHANG Shicheng, ZHANG Jingchen, et al. (2026) "Coupling mechanisms of fracture propagation and proppant transport indeep coalbed methane reservoirs," Coal Geology & Exploration: Vol. 54: Iss. 3, Article 9.
DOI: 10.12363/issn.1001-1986.25.10.0793
Available at: https://cge.researchcommons.org/journal/vol54/iss3/9

Reference

[1] 李渤,王彦卿,杨鸣一,等. 鄂尔多斯盆地中东部深层煤岩储层分布特征及成因[J]. 天然气地球科学,2025,36(9):1631−1645

LI Bo,WANG Yanqing,YANG Mingyi,et al. Distribution characteristics and genetic mechanisms of deep coal reservoirs in the central–eastern Ordos Basin[J]. Natural Gas Geoscience,2025,36(9):1631−1645

[2] 闫霞,熊先钺,徐凤银,等. 深部煤岩储层地质力学影响机制及控制因素:以鄂尔多斯盆地大吉区块为例[J]. 煤炭学报,2025,50(5):2550−2566

YAN Xia,XIONG Xianyue,XU Fengyin,et al. Deep coal geomechanical influence mechanism and its control factors of Daji Block in Ordos Basin[J]. Journal of China Coal Society,2025,50(5):2550−2566

[3] 孙晗森. 我国煤层气压裂技术发展现状与展望[J]. 中国海上油气,2021,33(4):120−128

SUN Hansen. Development status and prospect of CBM fracturing technology in China[J]. China Offshore Oil and Gas,2021,33(4):120−128

[4] 叶建平. 中国煤层气勘探开发及其科技进步历程回顾与思考[J]. 煤田地质与勘探,2025,53(1):114−127

YE Jianping. China’s CBM exploration and production and associated technological advancements:A review and reflections[J]. Coal Geology & Exploration,2025,53(1):114−127

[5] LIU Wei,PAN Zihao,ZHANG Xiong,et al. Experimental study of the fracture network expansion mechanism and three–dimensional reconstruction characteristic of high–rank coal in Guizhou Province,China[J]. ACS Omega,2023,8(7):6361−6375.

[6] 汤宇，孔祥伟，杨婉婷，等. 基于射孔倾角的深煤岩水力裂缝扩展及压裂液参数影响研究[J/OL]. 煤矿安全，2024：1–12 [2024-11-29]. https://doi.org/10.13347/j.cnki.mkaq.20241430.

TANG Yu，KONG Xiangwei，YANG Wanting，et al. Research on hydraulic fracture propagation and fracturing fluid parameters of deep coal rock based on perforation angle[J/OL]. Safety in Coal Mines，2024：1–12 [2024-11-29]. https://doi.org/10.13347/j.cnki.mkaq.20241430.

[7] EGERT R,JIN Wencheng,MENG Chunfeng,et al. Numerical study of proppant transport and settling processes in fractures[J]. GRC Transactions,2023,47:1−17.

[8] 张惜图,胡胜勇,武玺,等. 煤粉侵入对支撑裂缝渗透率的动态影响规律[J]. 煤炭学报,2024,49(5):2338−2346

ZHANG Xitu,HU Shengyong,WU Xi,et al. Dynamic influence of coal fine intrusion on propped fracture permeability[J]. Journal of China Coal Society,2024,49(5):2338−2346

[9] 陈瑞杰,熊志文,王瑞,等. 煤层顶板水力压裂裂缝扩展规律实验研究[J]. 中国矿业,2024,33(12):208−216

CHEN Ruijie,XIONG Zhiwen,WANG Rui,et al. Experimental study on the expansion law of hydraulic fracturing cracks in coal seam roof[J]. China Mining Magazine,2024,33(12):208−216

[10] 赵海峰,史宏伟,谢斐,等. 考虑微构造特征的深部煤层地应力模型及其应用[J]. 煤田地质与勘探,2025,53(11):120−129

ZHAO Haifeng,SHI Hongwei,XIE Fei,et al. A novel model for calculating in situ stress within deep coal seams considering microstructural characteristics and its application[J]. Coal Geology & Exploration,2025,53(11):120−129

[11] 孟尚志,侯冰,张健,等. 煤系“三气”共采产层组压裂裂缝扩展物模试验研究[J]. 煤炭学报,2016,41(1):221−227

MENG Shangzhi,HOU Bing,ZHANG Jian,et al. Experimental research on hydraulic fracture propagation through mixed layers of shale,tight sand and coal seam[J]. Journal of China Coal Society,2016,41(1):221−227

[12] HE Qiang,HE Bo,LI Fengxia,et al. Fractal characterization of complex hydraulic fractures in oil shale via topology[J]. Energies,2021,14:1123.

[13] 王振至,傅雪海,潘结南,等. 深部储层煤层气产出影响因素[J]. 煤田地质与勘探,2025,53(2):84−98

WANG Zhenzhi,FU Xuehai,PAN Jienan,et al. Factors influencing the production of coalbed methane from deep reservoirs[J]. Coal Geology & Exploration,2025,53(2):84−98

[14] YAN Hao,ZHANG Ran,ZHU Juhui,et al. Topology–based 3–D fractal characterization of fracture complexity in propagation experiment[J]. Thermal Science,2024,28(2A):1029−1035.

[15] DONTSOV E V,PEIRCE A P. Slurry flow,gravitational settling and a proppant transport model for hydraulic fractures[J]. Journal of Fluid Mechanics,2014,760:567−590.

[16] 龚爽,赵毅鑫. 层理对煤岩动态断裂及能量耗散规律影响的试验研究[J]. 岩石力学与工程学报,2017,36(增刊2):3723−3731

GONG Shuang,ZHAO Yixin. Effects of bedding on fracture characteristics and energy dissipation of coal under impact loading[J]. Chinese Journal of Rock Mechanics and Engineering,2017,36(Sup.2):3723−3731

[17] DENG Ding,LI Yuling,GUO Lianjun,et al. Experimental study on fracture and fragmentation characteristics of laminated rocks under impact loading[J]. Scientific Reports,2026,16:3861.

[18] 田鸿照,刘湘子,陈宗利,等. 致密气藏水力压裂支撑剂运移影响因素数值模拟[J]. 石油化工应用,2024,43(9):19−23

TIAN Hongzhao,LIU Xiangzi,CHEN Zongli,et al. Numerical simulation of factors affecting the migration of hydraulic fracturing proppants in tight gas reservoirs[J]. Petrochemical Industry Application,2024,43(9):19−23

[19] LIU Xin,XU Zhenyang,GUO Lianjun. An energy–based model with non–symmetrical branch fractures of different roughness[J]. Bulletin of Engineering Geology and the Environment,2024,83:320.

[20] 张景臣,石善志,郭晓东,等. 致密砾岩水力裂缝扩展大型矿场实验[J]. 深圳大学学报(理工版),2024,41(2):173−182

ZHANG Jingchen,SHI Shanzhi,GUO Xiaodong,et al. Large–scale mine experiments on hydraulic fracture expansion in dense conglomerates[J]. Journal of Shenzhen University (Science & Engineering),2024,41(2):173−182

[21] 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

[22] 杨火海,刘世凡,李富伟,等. 基于施工曲线特征识别的深部煤层压裂效果评价[J]. 中国石油勘探,2025,30(2):146−158

YANG Huohai,LIU Shifan,LI Fuwei,et al. Construction curve characteristics based fracturing results evaluation of deep coal seams[J]. China Petroleum Exploration,2025,30(2):146−158

[23] 李浩泽. 煤层压裂裂缝内支撑剂运移与压嵌机理[D]. 徐州：中国矿业大学，2023.

LI Haoze. Proppant transport and embedment mechanism in coal seam hydraulic fractures[D]. Xuzhou：China University of Mining and Technology，2023.

[24] 贾诏. 郑庄井田3号煤层压裂裂缝形态及特征研究[J]. 山西煤炭,2022,42(2):112−121

JIA Zhao. Fracture morphology and characteristics of No. 3 coal seam in Zhengzhuang mine field[J]. Shanxi Coal,2022,42(2):112−121

[25] 马兴莹,成小雨,程成. 煤岩层分段水力压裂裂缝扩展与应力演化特征实验研究[J]. 实验技术与管理,2024,41(9):47−53

MA Xingying,CHENG Xiaoyu,CHENG Cheng. Experimental study on fracture propagation and stress evolution characteristics of segmented hydraulic fracturing in coal strata[J]. Experimental Technology and Management,2024,41(9):47−53

[26] 尚校森,丁云宏,卢拥军,等. 一种页岩体积压裂复杂裂缝的量化表征[J]. 石油与天然气地质,2017,38(1):189−196

SHANG Xiaosen,DING Yunhong,LU Yongjun,et al. Quantitative characterization of complex fractures after volume fracturing in shale[J]. Oil & Gas Geology,2017,38(1):189−196

[27] 李铁军,李成玮,李曙光,等. 鄂尔多斯盆地DJ区块煤层压裂主控因素及最优区间[J]. 科学技术与工程,2021,21(29):12559−12565

LI Tiejun,LI Chengwei,LI Shuguang,et al. Main controlling factors and optimal interval of coal seam fracturing in DJ Block of Ordos Basin[J]. Science Technology and Engineering,2021,21(29):12559−12565

[28] 姚艳斌,马如英,孙晓晓. 深部煤层压裂液渗吸调控煤层气解吸增效机制[J]. 石油勘探与开发,2025,52(6):1388−1400

YAO Yanbin,MA Ruying,SUN Xiaoxiao. Mechanism of enhanced coalbed methane desorption regulated by fracturing fluid imbibition in deep coal seams[J]. Petroleum Exploration and Development,2025,52(6):1388−1400

[29] 汪杰,赵康佳,龚润璞,等. 压裂支撑剂在迂曲粗糙裂缝中运移沉降规律研究[J]. 长江大学学报(自然科学版),2025,22(1):81−90

WANG Jie,ZHAO Kangjia,GONG Runpu,et al. Study on migration and settlement rules of fracturing proppant in tortuous and rough fractures[J]. Journal of Yangtze University (Natural Science Edition),2025,22(1):81−90

[30] 崔传智,李景林,吴忠维,等. 复杂裂缝内支撑剂铺置规律及有效支撑面积[J]. 科学技术与工程,2023,23(30):12926−12935

CUI Chuanzhi,LI Jinglin,WU Zhongwei,et al. Proppant placement rule and effective supporting area in complex fractures[J]. Science Technology and Engineering,2023,23(30):12926−12935