Zhang Tianjun, Song Xianfeng, Pang Mingkun, Li Shugang, Lin Haifei, Zhang Tianyu, Pan Hongyu
College of Safety Science and Engineering, Xi'an University of Science and Technology, Xi'an, 710054, China.
Key Laboratory of Western Mine Exploitation and Hazard Prevention of the Ministry of Education, Xi'an, China.
Sci Rep. 2025 Oct 1;15(1):34271. doi: 10.1038/s41598-025-16481-9.
The fracture radius surrounding the borehole is a key parameter for assessing the effectiveness of acidizing and fracturing in coal seams. To determine this radius, a self-developed physical experimental platform for CO foam acidizing and fracturing in low-permeability coal seams was designed. Fracturing fluid erosion tests were carried out on raw coal samples, and the stress-strain relationship of the acidified coal around the borehole was analyzed. The effect of acidization on the intrinsic constitutive parameters of the surrounding coal was clarified, and an improved constitutive model for the coal body around the acidized fracturing borehole was established. It was found that increasing the erosion time of the fracturing fluid leads to reorganization of the coal body's physical structure, an increase in free volume, and enhanced compressibility and brittleness. Additionally, increasing the erosion period intensifies the chemical reactions within the minerals inside the pore fissures of the coal body, leading to more intense chemical reactions and significant brittle damage in the saturated samples. The improved damage constitutive model can accurately characterize the stress-deformation behavior of low-permeability coal seams under acid fracturing. Using this model, the effective fracturing radius of the 226 comprehensive working face was determined to be 5.2 m, and the "three-flower hole" borehole arrangement was proposed accordingly. This study provides theoretical guidance and significance for the borehole arrangement in acid fracturing of low-permeability coal seams.
钻孔周围的煤层破裂半径是评估煤层酸化压裂效果的关键参数。为确定该半径，设计了自主研发的低渗透煤层CO泡沫酸化压裂物理实验平台。对原煤试样进行了压裂液冲蚀试验，分析了钻孔周围酸化煤体的应力-应变关系。阐明了酸化对周围煤体本构参数的影响，建立了酸化压裂钻孔周围煤体的改进本构模型。研究发现，增加压裂液冲蚀时间会导致煤体物理结构重组、自由体积增加、压缩性和脆性增强。此外，延长冲蚀时间会加剧煤体孔隙裂隙内矿物的化学反应，导致饱和试样的化学反应更剧烈、脆性破坏更显著。改进后的损伤本构模型能够准确表征低渗透煤层在酸压裂作用下的应力-变形行为。利用该模型确定了226综采工作面的有效压裂半径为5.2 m，并据此提出了“三花孔”钻孔布置方式。该研究为低渗透煤层酸压裂钻孔布置提供了理论指导和意义。
