为了厘清氮气钻井井底岩爆动力学演化机理,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,基于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准,分别应用CWFS(cohesion weak-ening and frictional strengthening)-DP(Drucker-Prager)内聚力弱化摩擦力强度准则、DP 强度准则及 MC(Mohr-Coulomb)强度准则进行平行数值计算,得出了氮气钻井井底岩爆的动态演化过程.结果表明:井底逐渐靠近裂缝过程中致密砂岩基质会产生两种不同的破坏方式,即是沿着潜在剪切面,向井筒剪切滑移破坏及应力集中条件下的微剪切方式的挤压屈服破坏,直至破坏区延伸连通低压井筒,裂缝内的高压气体及岩爆碎屑释放大量能量,产生井底岩爆.研究成果可系统解释X8-2井井底岩爆发生前后随钻监测参数的异常变化,为准确判断氮气钻井井下工况提供了理论支撑,同时为及时采取针对性的对策措施提供了依据.
Numerical Simulation of Dynamic Evolution Mechanism of Rockburst in Nitrogen Drilling and Analysis of Rockburst Record Characteristics
In order to clarify the dynamic evolution mechanism of rock burst at the bottom of nitrogen drilling wells,a numerical model of gradually approaching fractures at the bottom of the well was established using the multi physics field coupling analysis software COMSOL Multiphysics 4.3.Based on the equivalent plastic strain corresponding to the initiation of micro fractures in tight sandstone rock masses,the CWFS(cohesion weakening and frictional strength)-DP(Drucker-Prager)cohesive force weakening friction strength criterion was applied.The dynamic evolution process of rock burst at the bottom of nitrogen drilling wells was obtained through parallel numerical calculations using the DP strength criterion and the Mohr-Coulomb(MC)strength criterion.The results indicate that as the wellbore gradually approaches the fracture,the dense sandstone matrix will exhibit two different modes of failure,namely,shear slip failure along the potential shear plane towards the wellbore and compression yield failure under stress concentration conditions through microshear,until the failure zone extends to connect to the low-pressure wellbore.The high-pressure gas and rock burst debris inside the fracture release a large amount of energy,resulting in bottomhole rock bursts.The research results can systematically explain the abnormal changes in monitoring parameters during drilling before and after the rock burst at the bottom of well X8-2,providing theoretical support for accurately determining the downhole conditions of nitrogen drilling,and providing a basis for timely and targeted countermeasures.
nitrogen drillingrock burstdynamic evolutionnumerical simulationrock burst record
万方数据
维普
