不同裂缝倾角诱导井底岩爆动态演化数值模拟

氮气钻井钻遇致密砂岩裂缝圈闭导致井底岩爆是QL1井恶性井喷事故的根本诱因,针对岩爆的动态演化过程进行系统分析并形成正确认识是恢复氮气钻井技术良性发展的紧迫需要.应用多物理场耦合分析软件COMSOL Multiphysics 4.3,建立井底逐渐接近裂缝的数值模型,以致密砂岩岩体内部微裂缝起裂时对应的等效塑性应变为判断标...

Numerical simulation of rock burst dynamic evolution at bottom hole induced by different fracture dip in nitrogen drilling

In order to restore the normal development of gas drilling technology, it is significant to gain a deep and comprehensive insight into rock burst dynamic evolution which is the essential reason of well QL1 accident. COMSOL Multiphysics 4.3 is applied to analyze this problem. The numerical model of bottom hole gradually close to the fracture is established, based on the equivalent plastic strain corresponding to the initiation of micro-cracks in tight sandstone rock mass as the judgment criterion, adopting the CWFS-DP(cohesion weakening and frictional strengthening-CWFS) strength criterion, DP strength criterion and MC strength criterion for parallel numerical calculation, the dynamic evolution process of bottom-hole rock burst induced by different fracture dip is obtained. The study shows that the larger the fracture inclination, the larger the critical distance of instability and the larger the volume of rock burst debris. The critical distance of horizontal fracture induced bottom-hole rock burst is the shortest (0.36m), and the rock burst volume is the smallest (0.096m3). The critical distance of 75° inclination fracture is the longest (0.42m), and the rock burst volume is 0.198m3. The dynamic evolution process analysis of rock burst at bottom hole can explain the abnormal change of logging monitoring parameters in DX1 well, which can not only provide theoretical basis for the prevention and control of rock burs, but also provide a new perspective for the deep rock dynamic instability in the field of petroleum engineering.