THREE-DIMENSIONAL POROELASTIC SIMULATION OF HYDRAULIC AND NATURAL FRACTURES USING THE DISPLACEMENT DISCONTINUITY METHOD

A three-dimensional fully-coupled poroelastic displacement discontinuity method is developed and used to analyze the temporal variation of opening and slip of a natural fracture in a reservoir in response to the sudden application of fluid pressure in the fracture surfaces. Numerical results show that a hydraulic fracture opens in an increasing manner with time as the rock moves towards a drained state under the applied stress. The applied pore pressure induces a time-dependent closure caused by the rock dilation. On the other hand, poroelastic analysis of a natural fracture subjected to shear shows that the fracture slip decreases with the time in response to a pore pressure-induced increase in the normal stresses on the joint. THEORY OF POROELASTICITY One of the main features of the deformation of fluid-saturated porous rock is its transient nature which is related to the presence of a fluid diffusion process, and is described by the linear theory of poroelasticity (Biot, 1941). Since the pioneering work of Biot, the theory of poroelasticity has been reformulated by a number of investigators, such as Rice and Cleary (1976), and Carroll (1980). The coupled constitutive equations of poroelastic material under isothermal conditions are (e.g., Rice &amp