石油科学通报2025，Vol.10Issue(6)：1199-1214,16.DOI:10.3969/j.issn.2096-1693.2025.03.024
层理倾角对富碳酸盐页岩裂缝扩展规律影响的直剪试验离散元模拟
Discrete element simulation of direct shear tests for investigating the influ-ence of bedding dips on fracture propagation in carbonate-rich shale
摘要
Abstract
This study focuses on the carbonate-rich shale of the lower Sha-3 to upper Sha-4 sub-members in the Dongying Sag of the Jiyang Depression within the Bohai Bay Basin.Based on the discrete element simulation and acoustic emission monitoring test methods,a numerical model for shale direct shear tests was constructed.The study systematically revealed the crack prop-agation laws and energy evolution characteristics under different bedding dip angles,and established a quantitative relationship between bedding dip angle,stress state,and the number of micro-fractures.The research results show that:(1)During direct shearing,high shear stress induces en echelon tensile fractures with an approximate 45° angle.After expansion,these fractures connect with shear fractures developed along the bedding to form a macroscopic fracture zone.As the bedding dip angle increases,the fracture zone gradually transitions from a stepped shape to a"zigzag"shape,exhibiting significant heterogeneity.(2)The shale fracture mechanism is dependent on the bedding dip angle:under low dip angles,shear fracture along the bedding is dominant;as the dip angle increases,the dominant fracture mechanism gradually shifts to matrix tensile-shear composite frac-ture.(3)The initiation stress of fractures is relatively low,and its variation with the bedding dip angle is not obvious;however,the damage stress and peak stress of fractures increase first and then decrease with the increase of the dip angle,reaching their peaks within the range of 40° to 50°.(4)Based on acoustic emission monitoring,it is found that crack propagation can be divided into three stages:initiation,rapid expansion(contributing 85%of the total number of cracks),and slow expansion.Tensile cracks account for 82.6%,while shear cracks(accounting for 17.4%)are mainly distributed along the bedding.(5)A comprehensive comparison of numerical simulation results,shale core fracture characteristics,and laboratory direct shear test results reveals similar fracture propagation laws,including shear fractures developed along the bedding plane and tensile fractures that obliquely cut(or penetrate)the bedding.The bedding dip angle is a key factor controlling the shale fracture development pattern,directly affecting the fracture propagation direction,complexity,and reconstruction volume.The findings of this study provide a theoretical basis for explaining the genetic mechanism and development pattern of natural fractures in continental shales,and also offer scientific support for the prediction of natural fractures in shale oil and gas exploration and development,which is of great significance for improving shale oil recovery efficiency and ensuring operational safety.关键词
离散元/声发射/页岩/裂纹扩展/破裂机制Key words
discrete element method/acoustic emission/shale/crack propagation/fracture mechanism分类
能源科技引用本文复制引用
LI Junliang,YUAN Guiting,YU Fusheng,WEI Xiaoliang,ZHANG Kuihua,FENG Haifeng,LIU Xinjin,LIU Zhina,QIN Feng,CHEN Tao,WANG Yong,YAN Jiajie..层理倾角对富碳酸盐页岩裂缝扩展规律影响的直剪试验离散元模拟[J].石油科学通报,2025,10(6):1199-1214,16.基金项目
国家科技重大专项"渤海湾盆地济阳坳陷古近系陆相页岩油勘探开发技术与集成示范"(2024ZD1405100)、国家自然科学基金企业创新发展联合基金项目(U24B6002)和中国石油化工集团有限公司项目(P23084、P24027)联合资助 （2024ZD1405100）
