Numerical Simulation of Fracture Permeability Change in Production ofPressure-sensitive Reservoirs with In-situ Stress Field

摘要

In pressure sensitive reservoirs, interaction effects among the porous media flow field, the fracture field and thestress field can cause some specific flow characteristics entirely different from those in conventional reservoirs. Dynamicfracture behavior is one of them, which generates a change in the value of fracture aperture and even a variation in theanisotropy of permeability. In this paper, we focus on the dynamic behavior of fractures and some affecting factors, includingdriving pressure and in-situ stress. Numerical discrete fracture network (DFN) models are built and solved by thefinite element method to investigate what the range-ability the fracture presents and what impact these affecting factorshave. In these mathematical models, both dynamic fractures and the fluid-solid coupling are taken into account, and astress-strain model, a flow field model and a fluid-solid coupling model are included. Based on the models, the variationof fracture aperture in pressure sensitive reservoirs is studied and the results show that a different direction andconnectivity of fractures lead fracture dilation to varying degrees as pressure changes so that the idea of anisotropic fractureporosity is proposed for reservoir scale simulation. The study also indicates that the drop of formation pressure determinesthe conductivity of fractures and anisotropy of permeability but just has a slight impact on the direction of principalpermeability. Finally, the study shows the interaction of the in-situ stress pressure and the fracture field.