煤田地质与勘探2025，Vol.53Issue(5)：36-45,10.DOI:10.12363/issn.1001-1986.25.01.0054
高压CO2泡沫压裂钻孔瓦斯渗流机理及方程改进
Mechanisms and equation improvement for gas seepage in coal seams around boreholes subjected to high-pressure CO2 foam fracturing
摘要
Abstract
[Objective]The special low-porosity,low-permeability structures of high-gas-content coal seams restrict effi-cient gas drainage.To address this issue,this study accurately determined the seepage parameters of annularly fractured coals around boreholes subjected to CO2 foam fracturing to enhance both the design accuracy of boreholes for gas pre-drainage from coal seams and gas drainage efficiency.[Methods]Using an independently developed apparatus for gas seepage experiments on fractured coals around boreholes,this study investigated the coals with pores and fractures dis-tributed in an annular pattern around boreholes from the perspective of varying initial pore structures.Specifically,this study analyzed the evolutionary characteristics of the permeability of fractured coals around boreholes by testing the per-meability of coal specimens with varying initial pore structures.Based on the improved Ergun equation,this study de-rived the fundamental equation for gas seepage in fractured coal media and verified its rationality.[Results]The results indicate that the annularly fractured coals around boreholes experienced three stages of rupture and deformations during their compaction.When the stress ranged from 1.2 kPa to 1.3 kPa,corresponding to the late deformation stage of particles,the quantity of fractured particles significantly decreased.The reason is that fine-grained particles produced be-fore the late stage of particle deformation filled most of the pores.Under external loading,the coal particles underwent further compression and deformation.As a result,the particles were subjected to mutual compression,forming a dense whole.As the seepage velocity continuously increased,the flow was primarily governed by inertial force.By setting parameters in the quadratic term coefficient in the Ergun equation at a variable associated with the flow state,it can be found that the relationship between the a/b ratio of the Ergun equation and seepage velocity v roughly followed a negat-ive exponential relationship.The improved Ergun equation overcame the limitations of the conventional seepage equa-tion,enabling the effective prediction of the negative pressure loss during seepage in porous media under varying poros-ities,particle diameters,and flow velocities.[Conclusions]For gas pre-drainage from coal seams,the permeability of annularly fractured coal around boreholes for gas pre-drainage can be calculated using the improved gas seepage equa-tion for fractured coals.Accordingly,the effective fracturing radius can be determined accurately.This study provides an important theoretical basis for optimizing the arrangement of gas drainage boreholes.Meanwhile,it offers a novel ap-proach to green,efficient gas drainage from widely distributed high-gas-content,low-permeability coal seams in China.关键词
能源安全/CO2泡沫压裂/裂隙扩展/渗流理论/渗流方程/渗透率Key words
energy security/CO2 foam fracturing/fracture propagation/seepage theory/seepage equation/permeability分类
矿山工程引用本文复制引用
庞明坤,张天宇,潘红宇,宋宪峰,伍珊,张天军..高压CO2泡沫压裂钻孔瓦斯渗流机理及方程改进[J].煤田地质与勘探,2025,53(5):36-45,10.基金项目
国家自然科学基金面上项目(52274226,52304253) （52274226,52304253）
西安科技大学优秀青年基金项目(2024YQ3-03) （2024YQ3-03）
