Kingfisher区块过断层地应力变化规律及井壁稳定性

Variations of In-situ Stress and Wellbore Stability for Kingfisher Block Through the Fault

Kingfisher区块断层发育,钻穿断层时井壁坍塌、钻井液漏失等复杂情况频发。根据孔隙弹性理论及Mohr-Coulomb强度准则,分析了正断层对地应力的影响规律,结合断层对地层力学性质的影响建立过断层时井壁稳定预测模型。结果表明,过正断层后垂直断层迹线水平应力明显增加;断层附近发育断层破碎带,使地层强度降低、坍塌压力升高;过断层时的安全泥浆密度窗口大大减小,为防止断层破碎带发生漏失,应以最小水平主应力作为安全泥浆密度窗口的上限;合理的钻井液密度及优良的封堵性是保证安全钻井的关键。研究结果与Kingfisher区块实钻情况吻合,对Kingfisher区块过断层时的钻井安全具有指导意义。

The development of faults is common in the Kingfisher block, causing frequently complicated situations, such as the wellbore collapse, the drilling fluid leakage and so on, in the process of drilling through faults. According to the pore elastic theory and the Mohr- Coulomb strength criterion, this paper analyzes the influence of the normal fault on the in-situ stress, which, combined with the influence of the faults on the formation and mechanical properties, is used finally to establish a prediction model of wellbore stability through faults. The results show that the horizontal stress perpendicular to the fault trace increases significantly through the normal fault; meanwhile, the fault fracture zone develops near the fault, and reduces the formation strength and increases the collapse pressure. The safe mud density window of the drilling fluid is greatly reduced with the fault. In order to prevent the drilling fluid leakage due to the fault fracture zone, it is necessary to consider the minimum horizontal principal stress as the upper limit of the safe mud density window. The reasonable drilling fluid density and the good sealing property of the drilling fluid are the key of the safety of drilling. The results of the study provide some guidance for the solid drilling situation of the Kingfisher block and the drilling safety of the Kingfisher block through the fault.