Understanding the Influence of Natural Fractures and Stress Anisotropy on Hydraulic Fracturing Design

Abstract

Abstract In general, hydraulic fracturing design for unconventional reservoirs is performed using planar fracture model simulators. It is well known that the presence of natural networks combined with varying stress anisotropy can significantly impact the overall stimulation process and hence, associated oil or gas recovery. In this study, a well-validated fracture simulator is used that explicitly accounts for the interaction between natural and hydraulic fractures under imposed stress anisotropy and performs transport of proppant in the induced complex network. Density of the natural fracture system is varied to study the scenarios, such as hydraulic fracture-governed mode and natural fracture-governed mode. For each of these scenarios, associated stress anisotropy is varied. These two parameters represent the properties of the formation that cannot be controlled. Then, multiple simulations are performed to understand the influence of design parameters, such as total slurry volume, pumping rate, and stage design for each set of fracture density and stress anisotropy. Many indicators are used, such as the stimulated fracture area, total proppant bed area, the area of the fracture above the bed, etc., to assess the efficacy of a design. This study shows that, depending on the natural fracture density and the stress anisotropy, the benefits of pumping larger volumes of fluid to create longer fractures and effectively distribute the proppant diminishes. It also reveals that modification of the stage design can be utilized to alleviate this problem. The capability to transport proppant by increasing the pumping rate is observed to be strongly dependent on natural fracture density. The result also shows the importance of these factors for whole pad optimization because the natural fractures and stress anisotropy can significantly alter the maximum fracture length. Thus, it becomes imperative to know the natural fracture distribution and the associated stress anisotropy to efficiently create a hydraulic fracturing design.