本煤层水压致裂增透范围分析

The analysis of antireflection range in coal seam hydraulic fracturing

在理论分析水压致裂起裂机理和起裂方向的基础上,应用煤岩损伤破裂过程渗流-应力耦合分析系统,对5种不同地应力条件下的本煤层水压致裂过程进行模拟,得到了煤体的起裂方向、起裂压力和扩展压力。研究发现:侧压系数λ<1时,煤体基本沿垂直方向起裂,起裂压力和扩展压力呈逐步增长的趋势;λ>1时,煤体的起裂方向为水平,起裂压力和扩展压力表现出平缓降低的趋势;在λ=1时,运用3种屈服准则进行了对比分析,得到了不同判别准则下的最小起裂水压。通过对λ=1.2时的受力状态进行深入分析,提出了压裂增透范围为宏观裂隙区、微裂隙贯通区、微裂隙产生区(受拉区)和原生裂隙扰动区(压应力恢复区)之和;利用数值图像处理得到的增透面积增长趋势符合二次函数的关系。

Based on the theoretical analysis of crack initiation mechanism and crack direction of hydraulic fracturing, the hydraulic fracturing process of coal seam under five different in-situ stress situations has been simulated by using the seepage-stress coupling analysis system of coal and/or rock damage fracture process, and hence, the crack initiation direction, initial pressure and expansion pressure have been obtained. Studies have found that, the crack direction is vertical, with the initial pressure as well as the expansion pressure presenting as gradual increasing trend when the lateral pressure coefficient λ1. When the lateral pressure coefficient λ1, the crack direction is horizontal, with the initial pressure and the expansion pressure presenting as gradually decreasing trend. When the lateral pressure coefficient λ=1, by carrying out three different kinds of yield criterion contrastive analysis, the minimum initial pressure are respectively obtained under the different kinds of yield criterion. Through the further stress analysis, i.e., when coefficient λ=1.2, studies have proposed that the antireflection range of hyd r a u l i c f r a c t u r i n g i s t h e s u m m a t i o n o f m a c r o- c r a c k z o n e, m i c r o- c r a c k c r o s s i n g zone, micro-crack generation zone（tension zone） and native crack disturbed zone（pressure recovery zone）; the growth trend of anti-reflection area which has been obtained by digital image processing accords with quadratic function.