A coupled hydraulic-mechanical-damage geotechnical model for simulation of fracture propagation in geological media during hydraulic fracturing

摘要

This paper proposed a coupled hydraulic-mechanical-damage (HMD) geotechnical model for simulating the entire failure process in geological media. In this model, elastic damage mechanics describes the damage process of elements. Darcy's Law and unsteady seepage flow equation describe fluid flow in elements, where compression of fluid and rock are considered. The coupled process is fulfilled by Biot's consolidation theory describing how pore-pressure affects the stress field and the stress/aperture/mesh-dependent permeability that represents the influence of stress on seepage field. The HMD model is implemented in the calculation module of Rock-Failure-Process-Analysis on Petroleum-problems (RFPA-Petrol) codes. The RFPA suite of software codes is based on the idea that the heterogeneity leads to non-linearity and causes progressive failure behavior observed in brittle rock. The capability of RFPA-Petrol simulator is demonstrated by a typical coupled problem related to double fractures propagation during hydraulic fracturing. This simulation successfully reproduces the asynchronous initiation, asymmetric growth and non-equal deflection of fractures in the numerical model. Then this simulator was used to investigate how fracture spacing and horizontal stress ratio influence propagation and reorientation of three hydraulic fractures from a horizontal well. At last, a horizontal well drilled by SHENGLI oilfield is simulated to certificate RFPA-Petrol's ability on field-scale models. It is found that larger fracture spacing and higher initial fracture height will form longer and wider fractured zones. HMD-based RFPA-Petrol is suitable for simulation of laboratory scale and field scale fracture propagation problems.