Simultaneous Multiple Plane to Plane Waterflooding in Fractured Tight Reservoirs
Waterflooding is common in conventional reservoirs, but efforts to apply waterflooding to unconventional tight oil formations have not met much success. The purpose of this research is to investigate the effectiveness of a novel 3-well pattern using horizontal wells (one injector and two producers, or one producer and two injectors) with multiple transverse hydraulic fractures nested to create arrays of plane-to-plane injector-producer waterflood displacements between propped hydraulic fractures.
The model for each plane-to-plane displacement uses pseudorelative permeability functions to account for conductive secondary fracture networks induced by hydraulic fracturing of the horizontal wells. Each pseudorelative permeability function is computed using inputs for the matrix and secondary fracture porosity and absolute permeability values, and matrix and secondary fracture relative permeability curves generated from Corey functions. To represent heterogeneity, input parameters are randomly generated, and the computed pseudorelative permeability functions are fit using Corey function parameters. Then we apply the Buckley-Leverett model for each displacement using the pseudorelative permeability curves. Finally, the pattern waterflood model accounts for the simultaneous multiple displacements using constant pressure well conditions and assuming minimal pressure losses along the wells and in the created hydraulic fractures.
Sensitivity studies have been carried out on a sample pattern with a smaller number of waterflood units undergoing plane-to-plane displacement, while full-scale simulation of a pattern with 408 waterflood units has been carried out to study the effectiveness of waterflooding in an unconventional reservoir using the proposed pattern. The study showed that pattern recovery factors increased for reduced secondary fracture porosity, and decreasing the hydraulic fracture spacing accelerated recovery. Further, rapid water breakthrough through in any individual displacement could short-circuit the displacement, and multiple short-circuits can cause poor pattern recovery efficiency. The proposed 3-well pattern offers a way to avoid well to well short-circuiting through propped fractures and enables a large number of simultaneous displacements. This work evaluates both the potential recovery efficiency increase and the potential risk and uncertainty related to the presence of induced secondary fractures.