Is Induced Fracture Complexity Always Required in Unconventional Reservoir Stimulation?

Abstract

Induced fracture complexity maximization, in addition to the primary hydraulic fracture, to improve the recovery efficiency or productivity of gas or liquids in unconventional resource shale reservoirs has been accepted and fully implemented by the industry. As a result, stimulation fluids and/or completion strategies have been engineered to maximize induced fracture complexity in many unconventional reservoirs. In typical unconventional horizontal completions, induced fracture complexity is beneficial for the productivity of nanodarcy (nd) shales if conductivity is sustained in time, although induced fracture complexity may not be a requirement for all unconventional reservoirs, especially tight sands.In some unconventional reservoirs, operators have observed similar productivity in wells with predominantly planar fractures compared to wells that appear to have more complex fractures. This paper, supported by extensive reservoir simulations, aims to develop criteria for situations in which induced fracture complexity and sustained conductivity are required and when they are not. The simulations include a reservoir permeability range of 10 nd to 0.001 md and a fracture complexity conductivity of 1 to 5 md-ft with and without stress dependence. The simulation results show that the fracture complexity with a constant and sustained conductivity (no stress dependent) are generally important for reservoir permeabilities lower than 100 nd for gas and 500 nd for liquid-producing reservoirs, but this benefit is minimized when the induced or existing stresses negatively affect the fracture complexity conductivity.Based on these results, an optimized completion strategy is suggested to maximize the productivity or recovery factor (RF) in unconventional gas-and liquid-producing reservoirs.