中文摘要：

分支井作为一种能够更加有效地开采油气藏的钻井技术，在国内外已经得到普遍推广。然而在应用该技术的实践中也遇到了一些新的难题，井壁稳定性就是其中之一。在前人研究的基础上，采用有限元方法建立分支井连接段的三维模型，综合考虑各向异性地应力，流体对岩石骨架的影响和方位角、倾角变化等，得出连接段附近的应力一应变和渗流场分布规律。并根据摩尔一库仑准则，利用有限元后处理程序图形化了井壁稳定的预测情况。分析结果表明：当支井方位角为90°，即与最大水平主应力平行时连接段井壁最稳定；井眼直径和连接段位置深度对井壁稳定性影响较小；后期生产压差过大也会增大裸眼完井井壁失稳的可能性。

英文摘要：

In recent years multilateral well drilling technology has become one of the mainstream technologies of the field of oil and gas exploration and development. But the technology also faces some new challenges, and borehole stability nearby the junctions is one of the serious problems. This paper establishes a three-dimensional model using finite element. Calculation and analysis of in-situ stress re-distribution caused by sidetrack drilling is made with consideration of the impact of initial pressure and steady-state Darcy flow. The stress concentration and distribution of displacement nearby the junction after sidetrack drilling are obtained through the finite element analysis of fluid-solid coupling calculation. According to Moore-Coulomb criterion, the stability of the connection section of wall projections is presented with graphics with the help of finite element post-processing program. The impact of the geometric parameters on borehole stability, such as borehole diameter, dip and azimuth is also discussed. The results show that： the most stable junction, independently of the depth of its placement and borehole diameter, is with the lateral wellbore axis oriented parallel to the maximum principal in-situ stress.