A hydraulic fracturing simulator for modeling a primary tensile fracture propagation interacting with a natural fracture system has been developed. In the simulator, the primary fracture is modeled by small segments aligned along the direction of maximum horizontal stress. These segments cause tensile failures sequentially according to increased fluid pressures. The natural fracture system is modeled using a three-dimensional discrete fracture network (DFN). Each fracture is stimulated by increasing fluid pressure and results in tensile opening or shear dilation. The fracturing simulator incorporates pressure-dependent apertures of the primary fracture as well as the natural fractures by converting their apertures to hydraulic properties of dual porosity model at each time step.
Using the developed simulator, we investigate effects of horizontal stress contrast and degree of shear dilation to a stimulated reservoir volume (SRV) quantitatively. A geomechanical model is constructed by using actual data sets gathered from a multi-stage hydraulic fracturing job at a tight oil reservoir in Japan. The SRV is calculated from the number and the distribution of the shearing fractures. Through the sensitivity studies, two distinct features are found. First, under high horizontal stress contrast, the large shear dilation contributes to create a wide SRV whereas the small shear dilation creates a narrow one. Second, the SRV created with the small shear dilation widens gradually when the state of horizontal stresses changes from a high contrast to a very low one. Consequently the size of the SRV shows almost equivalent regardless of the degree of the shear dilation. The dominant mechanism to make wider SRV varies depending the contrast of horizontal stress. Shear dilation dominants in high stress contrast and tensile opening in lower stress contrast, respectively.
