井底压差对垂直井井底应力场的影响研究

Study of effect of bottom-hole differential pressure on vertical well bottom-hole stress field

井底压差是影响钻井机械钻速的重要因素之一。实践证明欠平衡钻井与常规钻井相比机械钻速有显著提高,不同钻井条件下的井底应力场需要深入地研究。在分析井底岩石所受载荷的基础上,建立了轴对称条件下井底岩石流固耦合模型,并利用有限元方法进行求解,通过对不同井底压差下的井底岩石应力场进行数值模拟计算,针对井壁岩石的理论解和数值模拟结果进行对比验证模型的合理性,并对井底待破碎岩石进行了力学分析。结果表明,数值模拟结果与理论结果相符,验证了模型的正确性;井底待破碎岩石按照应力状态分为3个区域,分别为3向拉伸区、2向压缩区和3向压缩区。井底压差对井底应力场的影响研究为快速高效破岩提供理论基础。

Bottom-hole differential pressure is one of the important factors which affect the drilling penetration rate;and it is proved that underbalanced drilling is usually more efficient than conventional drilling.The purpose of the article is to study the effect of bottom-hole differential pressure on the vertical bottom-hole stress field.Based on the of mechanical analysis of the bottom-hole rock,the fluid-solid coupling model with the bottom-hole differential pressure is established under axisymmetric condition and the numerical simulation calculation of the bottom-hole stress field under different differential pressures is calculated with the finite element method.The comparison between the numerical and theoretical solutions and analysis of the stress state of bottom-hole rock to break are carried out.The results show that the numerical solution is consistent with the theoretical solution and the fluid-solid coupling model is reasonable.The bottom-hole rock is divided into three regions： triaxial tension region,biaxial compression region and triaxial compression region.Study of the bottom hole rock stress field under different drilling methods is the theoretical basis for faster and more efficient drilling.