We modify the Modified Cam‐Clay (MCC) model for large stress ranges encountered in geological applications. The MCC model assumes that the friction angle (ϕ) and the slope of the compression curve (λ) of a mudrock are constant and thus predicts constant values for the lateral effective stress ratio under uniaxial, vertical strain (K₀) and undrained strength ratio ( ). However, experimental work shows that λ, ϕ, and decrease and K₀ increases substantially with stress over large stress ranges (e.g., up to 100 MPa). We incorporate the stress dependency of λ and ϕ into the MCC model and use the new model to predict and K₀ ratios. The modified model, with only one additional parameter, successfully predicts the stress dependency of these ratios. We encode the modified model and use it for finite‐element analysis of a salt basin in the deepwater Gulf of Mexico. The stresses that the new model predicts around salt differ significantly from those predicted using the original model. We incorporate the stress dependency of the friction angle into the analytical models developed for critical tapers, wellbore drilling, and the stability of submarine channel levees. We show that the decrease of the friction angle with stress (1) results in a concave surface for critical wedges, (2) shifts the drilling window to higher mud weights and makes it narrower for a vertical wellbore, and (3) causes deep‐seated failure of submarine channel levees at lower angles. Our study could improve in situ stress and pore pressure estimation, wellbore drilling, and quantitative understanding of geological processes.

中文翻译：

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大应力范围的改进型Cam-Clay模型及其对地质和钻井过程的预测

我们针对在地质应用中遇到的较大应力范围修改了修改后的Cam-Clay（MCC）模型。MCC模型假定泥岩的摩擦角（ϕ）和压缩曲线的斜率（λ）是恒定的，因此可以预测单轴，垂直应变（K ₀）和不排水强度比下的侧向有效应力比的恒定值（ ）。然而，实验工作表明，λ，φ，和减少和K ₀在大应力范围大大增加与应力（例如，高达100兆帕）。我们整合的压力依赖性λ和φ进入MCC模型并使用新模型进行预测和K ₀比率。修改后的模型只有一个附加参数，可以成功预测这些比率的应力依赖性。我们对修改后的模型进行编码，并将其用于墨西哥湾深水盐盆地的有限元分析。新模型围绕盐预测的应力与使用原始模型预测的应力明显不同。我们将摩擦角的应力依赖性纳入到为关键锥度，井眼钻探和海底河道堤防稳定性开发的分析模型中。我们发现，随着应力的减小，摩擦角减小（1）导致关键楔形体陷于凹面;（2）将钻窗移至更高的泥浆比重，并使垂直井眼变窄;（3）引起深较小角度的海底河道堤坝就位故障。