不同预制裂缝角下紫砂岩的水力压裂声发射研究

Acoustic Emission of Purple Sandstone at Different Prefabricated Fracture Angles Under Hydraulic Fracturing

为了对紫砂岩在定向压裂下的岩石损伤与破坏过程进行研究与分析,选取300mm×300mm×300mm的紫砂岩岩样进行真三轴定向水力压裂模拟实验并进行了声发射监测。对实验中产生的声发射特征进行分析,根据事件率、能量率与注液压力的关系将压裂过程分为3个阶段:(Ⅰ)补充滤失阶段;(Ⅱ)能量累积和破坏阶段;(Ⅲ)能量残余阶段。由压裂过程的能量累积分析得出:随着预制裂缝角度的增加,能量累积表现出先减小后增大的趋势,且在预制裂缝角度为45°时累积能量到达最小值,此时裂缝偏转到相同偏转角度时裂缝延伸长度最短,偏转的最快,且随着预制裂缝方位角的增加,紫砂岩的起裂压力逐渐增加。

In order to study and analyze the damage and failure process of purple sandstone under directional fracturing,a true triaxial directional hydraulic fracturing simulation experiment was carried out with 300 mm × 300 mm × 300 mm of purple sandstone samples,and acoustic emission monitoring was carried out.The characteristics of acoustic emission produced in the experiment were analyzed.According to the relationship between event rate,energy rate and injection pressure,the fracturing process can be divided into three stages including(Ⅰ)supplementary filtration stage,(Ⅱ)energy accumulation and destruction stage,and(Ⅲ)energy residual stage.The energy accumulation analysis of fracturing process showed that with the increase of prefabricated fracture angle,the energy accumulation decreased first and then increased,and reached the minimum when the prefabricated fracture angle was 45°.When the fracture deflected to the same deflection angle,the fracture extension length was the shortest and the deflection was the fastest.With the increase of prefabricated fracture angle,the initiation pressure of purple sandstone increased gradually.