At the time of energy transition, it is important to be able to predict the effects of fluid overpressures in different geological scenarios as these can lead to the development of hydrofractures and dilating high-porosity zones. In order to develop an understanding of the complexity of the resulting effective stress fields, fracture and failure patterns, and potential fluid drainage, we study the process with a dynamic hydromechanical numerical model. The model simulates the evolution of fluid pressure buildup, fracturing, and the dynamic interaction between solid and fluid. Three different scenarios are explored: fluid pressure buildup in a sedimentary basin, in a vertical zone, and in a horizontal layer that may be partly offset by a fault. Our results show that the geometry of the area where fluid pressure is successively increased has a first-order control on the developing pattern of porosity changes, on fracturing, and on the absolute fluid pressures that sustained without failure. If the fluid overpressure develops in the whole model, the effective differential and mean stress approach zero and the vertical and horizontal effective principal stresses flip in orientation. The resulting fractures develop under high lithostatic fluid overpressure and are aligned semihorizontally, and consequently, a hydraulic breccia forms. If the area of high fluid pressure buildup is confined in a vertical zone, the effective mean stress decreases while the differential stress remains almost constant and failure takes place in extensional and shear modes at a much lower fluid overpressure. A horizontal fluid pressurized layer that is offset shows a complex system of effective stress evolution with the layer fracturing initially at the location of the offset followed by hydraulic breccia development within the layer. All simulations show a phase transition in the porosity where an initially random porosity reduces its symmetry and forms a static porosity wave with an internal dilating zone and the presence of dynamic porosity channels within this zone. Our results show that patterns of fractures, hence fluid release, that form due to high fluid overpressures can only be successfully predicted if the geometry of the geological system is known, including the fluid overpressure source and the position of seals and faults that offset source layers and seals.

中文翻译：

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浅地壳流体超压区的压裂和孔隙度窜流

在能量转换时，重要的是能够预测不同地质情景中流体超压的影响，因为这些会导致水力裂缝的发展和高孔隙度区域的扩张。为了深入了解由此产生的有效应力场、断裂和破坏模式以及潜在的流体排放的复杂性，我们使用动态流体力学数值模型研究了该过程。该模型模拟流体压力增加、压裂以及固体与流体之间的动态相互作用的演变。探索了三种不同的情况：沉积盆地、垂直带和可能被断层部分抵消的水平层中的流体压力增加。我们的结果表明，流体压力连续增加的区域的几何形状对孔隙度变化的发展模式、压裂以及无故障持续的绝对流体压力具有一阶控制。如果流体超压在整个模型中发展，有效微分和平均应力接近于零，垂直和水平有效主应力方向翻转。由此产生的裂缝在高岩性流体超压下发育并半水平排列，因此形成水力角砾岩。如果高流体压力积聚区域被限制在垂直区域内，则有效平均应力会降低，而差应力几乎保持不变，并且在低得多的流体超压下以拉伸和剪切模式发生破坏。偏移的水平流体加压层显示了一个复杂的有效应力演化系统，该层最初在偏移位置破裂，随后在层内形成水力角砾岩。所有模拟都显示了孔隙度中的相变，其中最初的随机孔隙度降低了其对称性，并形成了具有内部膨胀区的静态孔隙度波，并且在该区域内存在动态孔隙度通道。我们的结果表明，只有知道地质系统的几何形状，包括流体超压源以及偏移源层的密封和断层的位置，才能成功预测由于高流体超压而形成的裂缝模式，从而可以成功预测由于高流体超压而形成的流体释放和密封件。