Study on dynamic propagation of hydraulic fractures in enhanced thermal reservoir

Abstract

Micro-seismic data and post-fracturing production data have confirmed that the hydraulic fracture is an effective method to improve the production performance in enhanced thermal reservoir. While the mechanism of complex fracture network in fractured reservoirs is still not fully understood. This paper proposes a comprehensive model to simulate the fracture propagation by accounting for interactions with numerous natural fractures. We present a robust finite element model with adaptive insertion of two-dimensional cohesive elements for fracture propagation through the intact rock as well as the network of intersecting natural fractures. Cohesive elements are coupled with general Darcy's flow to incorporate fluid flow as well as elastic and plastic deformations of rock during initiation, propagation and closure of hydraulic fractures. From the simulation, it can be concluded that the composite stress factor was more suitable to indicate the ability of generating complex fracture network in fractured formation. In the simulation, there is a good correlation between composite stress factor and fracture complex index. The lower the composite stress factor is, the higher the fracture complex index is. When the composite stress factor is less than 4.6, the fracture complex index is greater than 3.5, which meant that it is much easier to generate complex fracture network when the composite stress factor is less than 4.6 under the same formation and operating technology.