Investigating the changes in matrix and fracture properties and fluid flow under different stress-state conditions

The fracture aperture and fracture permeability are usually considered to remain the same during the production life of a naturally fractured reservoir, regardless of the degree of depletion; but reservoirs experience different stress state conditions, therefore understanding the fracture behavior becomes more complex. This research analyzes the effect of fracture aperture and fracture permeability on the fluid flow under different overburden pressures. This research investigates the fracture apertures under different stress-state conditions. The equations to quantify the flow through the matrix and the fracture at different overburden pressures are provided. An X-ray CT scanner was used to obtain fracture aperture distributions at various overburden pressures to verify the use of log-normal distribution, which was commonly used for distributing fracture apertures. In addition, reservoir simulations are performed to duplicate the experimental results and to provide a valid model for future stress-sensitive reservoirs.
Our experimental results show that the fracture aperture and fracture permeability have significant pressure-dependent changes in response to applying variable injection rates and overburden pressures. The laboratory results show that the change in overburden pressure significantly affects the reservoir properties. The change in matrix permeability with different injection rates under variable overburden pressures is not significant in contrast with that effect on fracture aperture and fracture permeability. A calibration curve was obtained to determine fracture aperture from the X-ray CT scanner results. The aperture distribution from data obtained from X-ray CT scanner confirms lognormal distribution at various overburden pressures. This experimental research will increase the understanding of fluid flow behavior in fractured reservoirs.