Impact of fracture spacing and mechanical parameter anisotropy on fracture width in horizontal wells in shales.

摘要

The success of economically viable production of oil and gas from ultra-low permeability shale reservoirs depends on the creation of an extensive fracture network through hydraulic fracture stimulation. Multiple hydraulic fractures are created simultaneously in each stage to increase the surface area of contact between the wellbore and reservoir. The spacing between fractures is an important component to consider when developing an optimum stimulation design. An important aspect of shale rock properties is that shales are inherently anisotropic with a horizontal plane of isotropy (transversely isotropic) due to their finely layered structure. This study aims to provide an insight into the controlling effects of fracture spacing and different levels of rock property anisotropy on the fracture aperture during simultaneous fracture initiation and propagation. Multiple fracture propagation is simulated using 3-dimensional [3D] finite element models [FEM].;All simulations in this study include simultaneous propagation of four fractures in pre-defined planes using cohesive elements in a linear elastic medium. Numerous FEMs with varying spacing between fractures and varying levels of anisotropy are generated to analyze the effect of spacing and rock anisotropy on the fracture apertures. The modeling results show that there is a significant fracture width reduction in the center fractures when compared to the edge fractures across the entire range of fracture spacing included in the study. Previous studies present analyses on the effect of anisotropy on fractures whereas this study further investigates the individual effect of anisotropy on the edge fractures and center fractures. It can be taken further to simulate production rates and cumulative production over time and hence can be used as a guideline for different shale plays.