基于弹塑性损伤的软煤水压致裂渗流耦合数值模型

Coupled numerical model of hydraulic fracturing and seepage of soft coal based on elastoplastic damage

为指导煤矿井下软煤水压致裂的现场应用,基于弹塑性损伤理论进行软煤水压致裂渗流耦合数值模型研究。通过研究煤岩体孔隙度动态变化,推导出孔隙度-应变耦合模型,形成水压致裂的应力-渗流耦合模型和水压致裂煤体失效判据。结果表明,数值模拟结果与实际相符,软煤在压裂过程中同时发生剪切和拉伸破坏,小流量压裂时压裂半径小,大流量压裂时压裂半径大,同时出现了压裂范围在倾向方向大于走向方向的特征。软煤水压致裂的损伤过程与硬煤有较大区别,硬煤因裂缝长度扩展更快而压裂范围大于软煤,煤矿井下压裂后的半径考察结果与数值模拟预测结果相符。

In order to guide the field application of hydraulic fracturing of soft coal in underground coal mines,a study on the coupled numerical model of hydraulic fracturing and seepage of soft coal was carried out based on the theory of elastoplastic damage.By studying the dynamic changes of coal and rock mass,the porosity-strain coupling model was derived,forming a hydraulic fracturing stress-seepage coupling model and a hydraulic fracturing coal failure criterion.The numerical simulation results,which are consistent with reality,show that soft coal undergoes both shear and tensile failure during the fracturing process.The fracturing radius is small when fracturing with a small flow rate,and the radius is large when fracturing with a high flow rate.At the same time,the fracturing range is characterized by the fact that the tendency direction is larger than the strike direction.The damage process of hydraulic fracturing in soft coal is quite different from that in hard coal.Hard coal has a larger fracture range than soft coal due to the faster expansion of the fracture length.The investigation results of the radius after fracturing in underground coal mines are consistent with the results of numerical simulation predictions.