Article
Geosciences, Multidisciplinary
Yixin Lu, Zhaoping Meng, Xuefeng Su, Yina Yu
Summary: This study reveals the evolution of coal sample permeability during fracturing and establishes the relationship between coal sample fracture morphology and permeability. The results provide data support for the reformation of hydraulic fracturing in coalbed methane wells.
NATURAL RESOURCES RESEARCH
(2022)
Article
Energy & Fuels
Jun Li, Qiming Huang, Gang Wang, Enmao Wang
Summary: Active water fracturing is a commonly used technology for enhanced coalbed methane extraction, but the residues may block pore spaces in coal samples. Research indicates that the effect of active water treatment on methane adsorption behavior varies significantly between different types of coal samples. Further optimization of the active water formulation could reduce damage to coal seams.
Article
Energy & Fuels
Haitao Wen, Ruiyue Yang, Meiquan Lu, Zhongwei Huang, Chunyang Hong, Richao Cong, Xiaozhou Qin
Summary: This paper investigates the application of liquid nitrogen (LN2) cryogenic fracturing in the development of coalbed methane (CBM). The experimental results demonstrate that LN2 freeze-thaw fracturing is an effective method to create complex fracture patterns, thereby improving the stimulation efficiency.
GEOENERGY SCIENCE AND ENGINEERING
(2023)
Article
Thermodynamics
Wang Zepeng, Ge Zhaolong, Li Ruihui, Liu Xianfeng, Wang Haoming, Gong Shihui
Summary: Research has shown that acid based fracturing fluid (AFF) with appropriate hydrochloric acid (HCl) content is beneficial for the exploitation of coalbed methane (ECBM), while reducing costs and the risk of environmental pollution. The optimal HCl content range is between 3% and 5%. High HCl content in AFF enhances the effects on the adsorption pore structure, but is not conducive to ECBM.
Article
Energy & Fuels
Xiao Guo, Zihao Yu
Summary: In this article, the expansion law of hydraulic fractures in coal seams was studied through hydraulic fracturing experiments and numerical simulations. The results indicate that (1) high minimum horizontal stress difference in coal seams with undeveloped laminae confined the fractures within the coal reservoir, affecting multilayer fracturing. The high elastic modulus of the spacer facilitated vertical fracture expansion. Critical displacement played a vital role in vertical fracture breakthrough. Fracturing fluid concentration correlated with fracture height and inversely proportional to fracture length. (2) During the development of natural laminae in coal, fracture pressure decreased significantly. Fractures preferred to expand along the direction of laminae with a smaller angle to the maximum horizontal principal stress. When the adhesive strength of the interface was high, fractures passed directly through the interface to form vertical fractures. When interfacial cementation strength was low, cracks extended along the interface, turned to produce new vertical cracks, and eventually formed Z cracks.
PETROLEUM SCIENCE AND TECHNOLOGY
(2023)
Article
Energy & Fuels
Jienan Pan, Pengwei Mou, Yiwen Ju, Kai Wang, Qingzhong Zhu, Taoyuan Ge, Kun Yu
Summary: The variation characteristics of micro-nano-scale pores in a coalbed methane reservoir were studied after hydraulic fracturing using scanning electron microscopy, liquid nitrogen absorption, and mercury intrusion porosity measurements. It was found that the number of mesopores increased significantly after hydraulic fracturing, resulting in an increase in pore volume and pore specific surface area. The change characteristics of macropores were controlled by the coal's mechanical properties and in-situ stress. The elasticity of coal played a role in determining the type of pore modification, with coal that had larger elastic modulus and smaller Poisson's ratio experiencing brittle failure and increased pore connectivity after fracturing. In-situ stress inhibited pore expansion, leading to further pore compression.
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
(2022)
Article
Energy & Fuels
Pengwei Mou, Jienan Pan, Kai Wang, Jiang Wei, Yanhui Yang, Xianglong Wang
Summary: Hydraulic fracturing significantly increases the permeability of coal microfractures by expanding existing fractures rather than inducing new ones. The impact of hydraulic fracturing on microfractures is influenced by the heterogeneity of coal samples and differences in in-situ stress.
Article
Energy & Fuels
Xiaojie Fang, Caifang Wu, Hewei Zhang, Jiang Han, Geng Li, Bin Gao, Xiuming Jiang
Summary: The continuous injection of fracturing fluid redistributes stress, causing deformation and failure of coal. A fracture stress distribution model for cylindrical coal samples is developed based on triaxial compression experiments and hydraulic fracturing simulations. The concept of strain ratio (S) is proposed and its physical significance is explained. The deformation and failure process of coal samples during hydraulic fracturing is characterized by strain, fracture propagation, and AE energy.
Article
Computer Science, Interdisciplinary Applications
Jiangmei Qiao, Xuhai Tang, Mengsu Hu, Jonny Rutqvist, Zhiyuan Liu
Summary: This study found that in carbonate fracture-cavity reservoirs, natural fractures have a dominant impact on the propagation of hydraulic fractures, followed by the influence of confining stress. These two factors are critical to the design of hydraulic fracturing in carbonate fracture-cavity reservoirs.
COMPUTERS AND GEOTECHNICS
(2022)
Article
Geosciences, Multidisciplinary
Pengfei Ren, Qiong Wang, Dazhen Tang, Hao Xu, Shida Chen
Summary: In situ stress and coal structure are the key factors that influence hydraulic fracturing. The principal components analysis method is effective in simplifying logging data and improving recognition accuracy. Different stress fields result in different compositions and characteristics of coal seams and fractures.
NATURAL RESOURCES RESEARCH
(2022)
Article
Energy & Fuels
Hao Xianjie, Wei Yingnan, Yang Ke, Su Jian, Sun Yingfeng, Zhu Guangpei, Wang Shaohua, Chen Haibo, Sun Zhuowen
Summary: The study reveals significant anisotropic characteristics in coal reservoirs, with compressive strength decreasing with increasing bedding angle. Crack initiation strength and damage strength show a decreasing-then-increasing trend with variations in bedding angle.
PETROLEUM EXPLORATION AND DEVELOPMENT
(2021)
Article
Energy & Fuels
Shengcheng Wang, Shanjie Su, Dengke Wang, Peng Hou, Yi Xue, Xin Liang, Chengzheng Cai, Xianghe Gao, Yuhao Jin, Shuo Yang, Xuan Jiang
Summary: Liquid nitrogen fracturing is expected to be an effective method for increasing coalbed methane production due to its good reservoir adaptability. The advantages of ultra-low temperature and high gasification pressure during the fracturing process need further exploration.
GEOMECHANICS FOR ENERGY AND THE ENVIRONMENT
(2023)
Article
Energy & Fuels
Shaojie Zuo, Liang Zhang, Kai Deng
Summary: Exploiting coalbed methane is crucial for optimizing energy structure and enhancing coal mine safety. Tree type fracturing is an innovative technique that shows promise in addressing the limitations of conventional methods and enabling efficient coalbed methane extraction. The study of gas pressure and flow in gas-bearing coal after hydraulic fracturing provides valuable insights for further research and engineering applications of tree type fracturing.
Article
Energy & Fuels
Wenwen Chen, Xiaoming Wang, Mingkai Tu, Fengjiao Qu, Weiwei Chao, Wei Chen, Shihui Hou
Summary: This study uses variance analysis to analyze the impact of FFV and R-c/r on gas production in CBM vertical wells, and reveals the control mechanism of fracturing fluid on CBM migration. The results show that the appropriate FFV range depends on the ratio of R-c/r, and excessive or insufficient FFV will have a negative impact on gas production. This study provides guidance for the optimal design of hydraulic fracturing parameters for CBM wells.
Article
Thermodynamics
Jiawei He, He Li, Wei Yang, Jiexin Lu, Yi Lu, Ting Liu, Shiliang Shi
Summary: Acid fracturing is a potential method to enhance permeability in coalbed methane extraction, but its performance in coal reservoir is still unclear. This study characterized the surface morphology and internal pore structure of coal under matrix acidification and found that bituminous coal showed higher acid sensitivity and greater erosion rate and pore structure changes compared to anthracite. These results provide reference for selecting acid pad fluids for acid fracturing in different coal seams.