The flow characteristics of fractures are significantly affected by the stresses acting upon them. Reservoirs where the majority of the fluid flow is through fractures are very sensitive to the stress regime and its perturbations. Activities, such as production from a reservoir or injection into a reservoir, cause changes in the fluid pressure. This will alter the effective stress, which in turn will affect the flow of hydrocarbons through the fracture network. In order to understand how hydrocarbons flow within a fractured reservoir it is necessary to determine the influence of both stress and fluid pressure in a fracture network.
There have been many experimental studies showing the influence of stress on the flow of fluid through single fractures from which a relationship between fracture permeability and effective stress can be developed. Effective stress acting on a fracture can be established by considering the orientation of the fracture relative to the in-situ stress regime and the fluid pressure within the fracture. Once the effective stress acting on a fracture has been found the corresponding permeability can be assigned within a discrete fracture network (DFN) model. This approach then allows examination of stress-sensitive flow within fractured reservoirs.
This paper presents a methodology for incorporating in-situ stresses and stress changes due to production and injection in DFN modelling. The approach is significantly different from published methodologies on this subject, which are based on continuum porous medium modelling. By simulating and interpreting well tests in the fracture network during reservoir appraisal and after significant production, the presented approach would help in determining the influence of stress on hydrocarbon flow within a fracture network and to optimise future well locations and orientations.