Abstract:

In drilling engineering, the analysis of wellbore stability is directly related to the design of wellbore structure, the design of drilling fluid density window and the safety of drilling operations. Traditional strength criteria, due to mostly linear assumptions and the neglect of the intermediate principal stress effect, are difficult to accurately characterize the nonlinear failure characteristics of rocks under deep and complex geological conditions. Therefore, the selection of an appropriate strength criterion is the key to accurately evaluating wellbore stability. This paper uses an improved three-dimensional Hoek-Brown strength criterion and combines theoretical research with model application to establish a wellbore stability evaluation model that is more in line with actual working conditions. The research results show that this criterion not only retains the nonlinear characteristics of the Hoek-Brown strength criterion in the meridian plane, but also considers the influence of the intermediate principal stress on rock strength. The yield surface of the improved three-dimensional criterion in the principal stress space is a conical surface, and the yield curve satisfies the properties of being outwardly convex, smooth and closed. Through the comparative analysis of the true triaxial test data of six different rocks, it is proved that this criterion has good applicability to various rocks. When this criterion is applied to the wellbore stability analysis of the Jialingjiang Formation limestone strata in the Tongluoxia Gas Field in the eastern Sichuan Basin, the calculated collapse pressure equivalent density is 1.16 g/cm³. When drilling along the direction of the maximum horizontal principal stress, the collapse pressure equivalent density is the lowest, which is in line with the actual working conditions and is superior to the other four traditional strength criteria. The improved three-dimensional Hoek-Brown strength criterion provides a more accurate and practical method for wellbore stability analysis.

Key words: improved three-dimensional Hoek-Brown strength criterion, yield surface, yield curve, wellbore stability, collapse pressure equivalent density

摘要：

在钻井工程中，井壁稳定性分析直接关系到井身结构设计、钻井液密度窗口设计及钻井施工安全。传统强度准则因大多为线性假设和忽略中间主应力效应，难以准确表征深部复杂地质条件下岩石的非线性破坏特征，所以选取适宜的强度准则是准确评价井壁稳定性的关键。本文使用了一种改进的三维Hoek-Brown强度准则，通过理论研究与模型应用相结合的方式，建立了更符合实际工况的井壁稳定性评价模型。研究结果表明：该准则不仅保留了Hoek-Brown强度准则在子午面内的非线性特征，还考虑了中间主应力对岩石强度的影响。改进的三维准则在主应力空间中的屈服面呈圆锥形曲面，屈服曲线满足外凸、光滑且封闭的性质。通过对六种不同岩石真三轴试验数据的对比分析，证明了该准则对各类岩石的良好适用性。将该准则应用于川东铜锣峡气田嘉陵江组灰岩地层的井壁稳定性分析，计算得到坍塌压力当量密度为1.16 g/cm³，在沿最大水平主应力方向钻进时，坍塌压力当量密度最低，符合实际工况，优于其他四种传统强度准则。改进的三维Hoek-Brown强度准则为井壁稳定性分析提供了一种更加精确且实用的方法。

关键词: 改进的三维Hoek-Brown强度准则, 屈服面, 屈服曲线, 井壁稳定, 坍塌压力当量密度

CLC Number: 

• TE21

• P618.13