煤岩断裂力学性质对储层压裂改造的影响

Fracture properties of high-rank coal and its constraint on hydraulic fracturing stimulation of coal reservoir

煤岩断裂力学性质是煤储层水力压裂改造的重要力学约束,查明煤岩断裂力学性能及其对储层压裂造缝效率的影响机制对于压裂工艺优化、造缝效果改善具有现实意义。以阿拉善二道岭矿区深部(>1 800 m)高阶煤岩为对象,采用压痕法(IM)测试计算了煤岩的维氏硬度(Hν)及断裂韧度(KIC),探讨了在不同压头载荷施加条件下煤岩维氏硬度、断裂韧度值的变化规律,对比分析了低(100 g)、中(500 g)、高(1 000 g)三级压头载荷施压作用下,煤岩的破碎效率及造缝效果,提出高阶脆性煤岩在受压断裂过程中存在阶段式顿挫效应。研究认为:煤储层水力压裂应考虑脆性煤岩辐射裂缝延展效应,采取压裂液逐级变排量注入技术(及时充注新生成的裂缝空间),以维持较高裂缝净压力,产生更大的应力强度因子,提高储层压裂造缝效率,研究结果可为深部高阶煤储层水力压裂改造理论深化与效率提升提供科学参考。

Fracture mechanics of coal rock is an important mechanical constraint of hydraulic fracturing stimulation of coal reservoir. It is of practical significance to find out the fracture properties of coal rock and the influencing mechanisms of hydraulic fracturing efficiency on coal reservoir for fracturing technology optimization and fracturing effect improvement. Taking the high-rank coal sampling from Erdaoling deep mining area(>1 800 m)in Alxa as an object,the vickers hardness(Hν)and fracture toughness(KIC)of coal rock were calculated,the indentation method(IM)tests were carried out,the evolution rule of the vickers hardness,fracture toughness values under different indenter pressure were discussed,the fracturing efficiency and stimulation effect of coal rock imposed low(100 g),medium(500 g),high(1 000 g)indenter pressure were analyzed in contrast,and the stage abortion effect in the process of fracturing was proposed. The studies suggest that coal rock brittleness crack extension effect in hydraulic fracturing of coal reservoir should be considered,variable displacement injection technology should be taken(filling the newly generated space of fractures in time),to maintain higher fracture net pressure and greater stress intensity factor,improving the efficiency of reservoir fracturing. This study can provide a scientific reference for hydraulic fracturing theory deepening and the stimulation efficiency optimizing of deep high-rank coal reservoirs.