A Mathematical Model and Numerical Simulation of Waterflood Induced Dynamic Fractures of Low Permeability Reservoirs

Abstract

Abstract As a powerful technique for reservoir simulation, the embedded discrete fracture model (EDFM) has been widely used for unconventional fracture reservoirs. However, the appearance of dynamic fractures caused by fracture extension during well stimulation brings significant challenge to reservoir simulation. We presented a new numerical method to model the dynamic fracture performance for horizontal wells in unconventional reservoirs by using EDFM in this study. The proposed method includes a numerical model and a workflow to simulate water-oil flow in an unconventional fracture reservoir. The fracture dynamics are not only considered into the pressure-dependent properties of fractures (such as fracture permeability, porosity), but also incorporated into EDFM by activating or deactivating grid blocks of fractures at each time step. Fracturing treatment data during stimulation and microseismic data after hydraulic fracturing provide a quantitative understanding of the dynamic fracture behaviors, including fracture location and geometries with time. We conducted a comparative analysis with respect to static fracture properties and dynamic fracture properties. In comparison to static fractures, dynamic fractures have a substantially higher bottomhole pressure. We also analyzed how production was impacted by shut-in time and water injection rate. Different production systems have varying cumulative oil and water production, and an optimal production system was identified. The quantitative understanding of fracture dynamics for field application examples helps to achieve more accurate production estimation.