LAUSR

Wellbore stability analysis is a growing concern in oil industries. There are many parameters affecting the stability of a wellbore including geomechanical properties (e.g., elastic modulus, uni-axial compressive strength (UCS) and cohesion) and acting forces (e.g., field stresses and mud pressure). Accurate determination of these parameters is time-consuming, expensive and sometimes even impossible. This work offers a systematic sensitivity analysis to quantify the amount of each parameter’s effect on the stability of a wellbore. Maximum wellbore wall displacement is used as a stability factor to study the stability of a wellbore. A 3D finite difference method with Mohr model is used for the numerical modeling. The numerical model is verified against an analytical solution. A dimensionless sensitivity factor is developed in order to compare the results of various parameters in the sensitivity analysis. The results show a different order of importance of parameters based on rock strength. The most sensitive properties for a weak rock are the maximum horizontal stress, internal friction angle and formation pressure, respectively, while for a strong rock, the most sensitive parameters are the maximum horizontal stress, mud pressure and pore pressure, respectively. The amount of error in wellbore stability analysis inflicted by the error in estimation of each parameter was also derived.摘要井眼稳定性分析在石油工业中得到越来越多的关注。影响井筒稳定性的参数很多,包括地质力学性 质(如弹性模量、轴向抗压强度和黏聚力)和作用力(如场应力和泥浆压力)。精确地确定这些参数不仅耗时、 价格昂贵,有时甚至是不可能的。本文提供了一种系统的灵敏度分析法,以量化每个参数对井筒稳定性的 影响程度。利用最大井壁位移作为研宄井筒稳定性的一个稳定因子。采用Mohr模型的三维有限差分法进 行数值模拟,用解析解对数值模型进行了验证。为了比较各种参数在灵敏度分析中的结果,提出了一种无 量纲灵敏度因子。结果表明,根据岩石强度的不同,参数的重要程度是不同的。对于软岩石,最敏感的参 数分别是最大水平应力、内摩擦角和地层压力,而对于强岩石,最敏感的参数分别是最大水平应力、泥浆 压力和孔隙压力。本文也推算了每个参数的估计误差对井眼稳定性分析的误差的影响。