Article
Engineering, Chemical
Qing Chen, Zhiqiang Huang, Hao Huang, Qi Chen, Xingjie Ling, Fubin Xin, Xiangwei Kong
Summary: Coalbed methane reservoirs are susceptible to coal fines generation during hydraulic fracturing, which negatively impacts the conductivity of the propped fracture. This study conducted conductivity tests on coal rock fractures to assess the effect of particle size ratio in composite proppant blends on fracture conductivity. The findings indicate that controlling the proportion of large and small particles is important for short-term and long-term conductivity, respectively, for efficient hydraulic fracturing in coalbed methane reservoirs.
Article
Engineering, Geological
Xitu Zhang, Shengyong Hu, Yongxin Hao, Guorui Feng, Siyuan Li, Zhaoying Chen
Summary: This study investigates the impact of coal fine retention on the permeability of hydraulic propped fractures through experiments and modeling. It reveals that an increase in coal fine flow rate decreases retention, increases porosity, and enhances permeability in fractures; larger coal fine particles tend to retain more, impacting the fracture permeability significantly.
ROCK MECHANICS AND ROCK ENGINEERING
(2022)
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
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
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
Geosciences, Multidisciplinary
Yanjun Lu, Jinxuan Han, Hua Zhang, Zhenping Xu, Zhaozhong Yang, Manping Yang, Junfeng Guo, Hongjian Zhu, Yu Qi
Summary: This research focuses on the microstructure, wettability, permeability, rock mechanics, and in-situ stress of coal in the Zhengzhuang block for the effective exploitation of Coalbed Methane (CBM). The study reveals that high rank anthracite with high vitrinite content and low inorganic mineral content is abundant in CBM. The wettability of coal varies with burial depth, and the contact angles with active water and foam fracturing fluid decrease as the depth increases. Fracture pressure and closure pressure gradients are higher in the No.3 coal seam compared to the No.15 coal seam. The comprehensive understanding of coal properties and engineering practice provides guiding significance for CBM exploitation in the Qinshui Basin.
FRONTIERS IN EARTH SCIENCE
(2023)
Article
Energy & Fuels
Ruiyue Yang, Haitao Wen, Zhongwei Huang, Bo Zhang, Haizhu Wang, Bin Wang, Nikita Dubinya
Summary: A new compound fracturing method combining liquid nitrogen (LN2) fracturing and hydraulic fracturing is proposed in this study to improve the efficiency of hydraulic fracturing in coalbed methane (CBM) reservoirs. Lab results show that the compound fracturing method can create more complex and highly conductive fracture networks compared to traditional fracturing methods.
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
Geosciences, Multidisciplinary
Jinbin Zhao, Peng Liu, Junjun Li, Zhaoying Chen, Yang Li, Feng Li
Summary: This paper uses microseismic technology to monitor the spatial and temporal characteristics of fracture extension during hydraulic fracturing in the CBM well. The study quantifies the three-dimensional shape of fractures and finds that the development of fractures is intermittent. After fracturing with a large amount of fracturing fluid injection, the fracture area has significantly increased, and gas production has improved.
FRONTIERS IN EARTH SCIENCE
(2023)
Article
Engineering, Geological
Yiyu Lu, Jingwei Zheng, Zhaolong Ge, Zhe Zhou, Haoming Wang, Liang Zhang
Summary: This study conducted experiments on the fracturing of coal using a true tri-axial testing system with supercritical CO2 (SC-CO2) as the fracturing fluid. The results showed that compared to hydraulic fracturing, SC-CO2 reduces the pressure required to initiate fractures by approximately 32-41%. This reduction is attributed to the increased percolation and pore pressure effects of SC-CO2, which in combination with the highly developed pore/fracture structure of coal, leads to the formation of a complex fracture network. The fractal dimension is positively correlated with the injection rate and temperature during SC-CO2 fracturing, indicating the potential for increased coalbed methane production under high injection flows and temperature.
ROCK MECHANICS AND ROCK ENGINEERING
(2022)
Article
Energy & Fuels
Shaojie Zuo, Shouqing Peng, Dongping Zhou, Changwei Wang, Liang Zhang
Summary: An analytical model of calculating the initiation pressure during hydraulic fracturing with multiple tree-type branch boreholes (TTBBs) was established in this study, considering the mutual influence of TTBBs in different layers. The circumferential stress of TTBB T-2 was found to first increase and then decrease with the distance to the fracturing borehole under the influence of adjacent TTBBs, eventually approaching the stress value of a single TTBB. The theoretical initiation pressure decreased with increasing number of TTBBs and TTBB layers.
GEOMECHANICS AND GEOPHYSICS FOR GEO-ENERGY AND GEO-RESOURCES
(2022)
Article
Energy & Fuels
Xianglong Wang, Jienan Pan, Kai Wang, Pengwei Mou, Jianxin Li
Summary: This study conducted a laboratory simulation of hydraulic fracturing in coal and used X-ray computer tomography (CT) and digital volume correlation (DVC) to analyze and quantify the changes in fractures induced by hydraulic fracturing. The results showed that hydraulic fracturing increased the aperture, volume, and surface area of fractures in coal, and simplified their morphology. The study also revealed the significant influence range and connectivity of fractures caused by hydraulic fracturing.
INTERNATIONAL JOURNAL OF COAL GEOLOGY
(2022)
Article
Energy & Fuels
Hui Wang, Yanbin Yao, Dameng Liu, Yidong Cai, Yanhui Yang, Shengqiang Zhou
Summary: This study proposes a well logging coal structure index (WCSI) to quantify coal deformation and its impact on coalbed methane productivity. The results show that the degree of coal seam deformation affects reservoir permeability and hydraulic fracturing effectiveness, subsequently influencing gas production rate. The WCSI is found to be a useful parameter for preliminary forecasting of gas production in the southern Qinshui Basin.
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
(2022)
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.
