Hydraulic fracturing design for shale oils based on sweet spot mapping: A case study of the Jimusar formation in China

Abstract

Multistage fracturing horizontal well is the main method of shale oil development. However, significant differences are observed between fracturing stages productivity due to reservoir heterogeneity. Therefore, it is necessary to incorporate reservoir heterogeneity characterization in hydraulic fracturing design so that ineffective clusters can be minimized. Taking the Jimusar formation as example, we apply an integrated fracturing design workflow that considers reservoir heterogeneity characteristics through sweet spot mapping to arrive at the optimum fracturing treatment. The geological and geomechanics models are constructed utilizing logs and core laboratory tests, from which the geological sweet spot (GSS) and engineering sweet spot (ESS) mapping are obtained. The GSS and ESS are later classified with respect to three different levels: type I (good), type II (medium) and type III (poor), based on which four sweet spot combinations are selected for fracturing design. Unconventional fracture model (UFM) is applied for the generation of complex fracture network, and performs productivity evaluation through reservoir numerical simulation. The simulation results suggest that to maximize the fluid withdrawal within stimulated region by reducing the productivity difference between stages, the fracturing scale of the stage containing type I GSS combination should be smaller than that of type II/III GSS in jimusar formation. And for regions with the same type GSS, the fracturing scale containing the type I ESS combination should be kept smaller than that of the type II/III ESS. The workflow will be helpful for the reservoir engineers in developing a reasonable fracturing plan that maximizes production performance or economic benefit for shale oil in future operations.