脉动水力压裂过程中煤层应力扰动特征的数值模拟分析

摘要

The pulsating hydro-fracturing (PHF)of coal beds is a new technology based on the conventional hydraulic fracturing and pulsating water injection.Currently,the study on stress disturbance features caused by PHF is not sufficient.Based on the continuum mechanics,a stress-response numerical model was presented here to simulate the formation of disturbance stress during PHF by applying the schemes of staggered-grid finite difference.The disturbance stress distribution,the effective stress disturbance area,and the influences of different formation mechanical parameters on stress distribution during PHF were investigated.The results showed that the stress disturbance caused by PHF has an extensively affecting area and a regional stress concentration,they generate the focusing effect;the shear stress generated causes a tensile damage of coal rock during PHF to form a much larger effective stress disturbance zone than that for the quasi-static fracturing;the strong compressibility of coal beds can be used to cause a much bigger stress disturbance and damage zone,which will improve the PHF effect.The results provided a guidance for studying the stimulation mechanism of PHF in coal beds.%煤层脉动水力压裂是在煤层常规水力压裂与脉动注水基础上提出的一项新技术，但目前针对脉动压裂过程中地应力扰动特点的研究尚不充分。基于连续介质力学，采用交错网格有限差分，建立了脉动载荷下地应力响应数值模型，研究了脉动压裂过程中地层扰动应力的分布、有效扰动范围及不同地层力学参数对应力扰动的影响，发现脉动水力压裂引起的应力扰动具有以下特征：波及范围广、区域性应力集中，可产生会聚效应；可引起切应力使煤层产生拉伸损伤，形成远大于准静态压裂的有效应力扰动区；可利用煤岩的强压缩性产生更大范围的应力扰动与损伤区，提升压裂效果。该成果可望为煤层脉动水力压裂增产机理研究提供参考和依据。