We predict stresses and strains in the Tarfaya salt basin on the West African coast using a 3D static geomechanical model and compare the results against a simplified 2D plane-strain model. Both models are based on present-day basin geometries, are drained, and use a poroelastic description for the sediments and visco-plastic description for salt. We focus on a salt diapir, where an exploratory well has been drilled crossing a major fault. The 3D model shows a significant horizontal stress reduction in sediments at the top of the diapir, validated with measured data later obtained from the well. The 2D model predicts comparable stress reduction in sediments at the crest of the diapir. However, it shows a broader area affected by the stress reduction, overestimating its magnitude by as much as 1.5 MPa. Both models predict a similar pattern of differential displacement in sediments along both sides of the major fault, above the diapir. These displacements are the main cause of horizontal stress reduction detected at the crest of the diapir. Sensitivity analysis in both models shows that the elastic parameters of the sediments have a minimal effect on the stress–strain behaviour. In addition, the 2D sensitivity analysis concludes that the main factors controlling stress and strain changes are the geometry of the salt and the difference in rock properties between encasing sediments and salt. Overall, our study demonstrates that carefully built 2D models at the exploration stage can provide stress information and useful insights comparable to those from more complex 3D geometries. Thematic collection: This article is part of the Mechanics of salt systems: state of the field in numerical methods collection available at: https://www.lyellcollection.org/cc/mechanics-of-salt-systems

中文翻译：

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西非海岸塔法亚盆地盐结构的 3D 与 2D 地质力学建模应力比较

我们使用 3D 静态地质力学模型预测西非海岸塔法亚盐盆地的应力和应变，并将结果与​​简化的 2D 平面应变模型进行比较。两种模型都基于当今的盆地几何形状，被排干，并对沉积物使用多孔弹性描述，对盐使用粘塑性描述。我们专注于盐底辟，在那里已经钻了一个穿越主要断层的探井。3D 模型显示底辟顶部沉积物的水平应力显着降低，并通过后来从井中获得的测量数据进行了验证。二维模型预测底辟顶部沉积物的应力降低相当。然而，它显示受应力降低影响的区域更广，高估了其幅度高达 1.5 MPa。两种模型都预测了底辟上方主断层两侧沉积物的类似差异位移模式。这些位移是底辟顶部检测到的水平应力降低的主要原因。两种模型的敏感性分析表明，沉积物的弹性参数对应力-应变行为的影响很小。此外，二维敏感性分析得出的结论是，控制应力和应变变化的主要因素是盐的几何形状以及包裹沉积物与盐之间岩石性质的差异。总的来说，我们的研究表明，在勘探阶段精心构建的 2D 模型可以提供与更复杂的 3D 几何结构相媲美的应力信息和有用的见解。专题合集：