Hydromechanical Modeling of Tectonically Driven Groundwater Flow

Abstract:

Groundwater flow in bedrock is mainly controlled by the distribution of fractures and faults formed by tectonics. Understanding the formation of fractures and faults due to crust movement and their effects on groundwater flow are important in assessment and development of the groundwater resources in fractured rocks. A three-dimensional solid-fluid coupling model of a homogeneous or heterogeneous cubic bedrock was built with the finite difference model FLAC3D to simulate the rock deformation and fluid flow induced by the crust movement during 10000 years. Two opposite velocity boundary conditions on the left and right part of model were used to simulate the shear stress due to the crust movement. The results indicate that for the homogeneous formation the high compressive stresses and thus the maximum pore pressure concentrate along the middle of formation as time progresses. The pore pressure along the middle of formation increases at early time, then approaches a peak value, and finally decreases as time progresses, indicating that the plastic failure of the formation may happen along the middle of formation where the fluid flow is changed by stresses. The heterogeneous case considered is that the mechanical and hydrological properties are different in one half of the formation from the other half. In this case the distribution and change of the stresses and pore pressure are similar with the homogeneous case while the magnitudes are smaller. The results of this study can help one to understand the effects of tectonics on the groundwater flow in fractured rocks.

Keywords: solid-fluid coupling model, stresses, pore pressure, groundwater flow