Abstract
Economical production of shale resources requires drilling horizontal wellbores with either sequential or zipper-frac completion in order to increase the fracture complexity in tight reservoirs. Properly estimating the final fracture geometry is the primary challenge in these compound fracturing practices. Various parameters control the fracture geometry including: fracture spacing, in-situ differential stress, pump rate and fluid viscosity. Two important fracture characteristic that should be addressed in such a complex system in order to have a proper estimation about fracture geometry, are fracture height and out of plane propagation. Although the modeling of hydraulically driven fractures in such a medium has been advanced over the past decades, there have been a few attempts to investigate these two phenomena together in an implicit model.
This article advances a hydraulic fracture model that predicts single and multi-fracture propagation. The model simultaneously simulates the dynamic growth of multiple fractures while addressing the stress interference between the fractures and its effect on fracture propagation. The hydraulic fracture model is based on displacement discontinuity method for simulating fracture propagation in multi-fracture systems. Using the simulator, variations in the parameters affecting the behavior of hydraulic fractures were explored. The simulator is able to predict non-planar fracture propagation due to stress interference between adjacent fractures. For studying fracturing fluid, fluid flow equations are solved using finite difference and are fully coupled with geomechanical solver. The effect on fracture propagation from variations in fluid viscosity, injection rate, stress interference, fracture spacing, stress anisotropy and perforation direction are presented for a multi fracture system.
The result of this study indicates that stress shadowing is the main factor affecting hydraulic fracture propagation. It changes the direction and magnitude of the principal stresses around fractures and may cause early screen out or tortuosity in fractures created from single or multiple wells. Therefore, an optimized fracture spacing is needed for placing more fracture into the system. The results of this study would help operators to better optimize the fracture spacing in horizontal wellbores and maximize the complexity needed for a typical horizontal fracturing job.
