Productivity enhancement by stimulation of natural fractures around a hydraulic fracture using micro-sized proppant placement

Abstract

Hydraulic fracturing in naturally fractured rocks interconnects a natural fracture network to the wellbore. Improving the connectivity between a hydraulically created fracture and the pre-existing natural fractures can significantly improve the hydraulic fracturing efficiency. In this study, a well stimulation method is proposed to enhance the conductivity of fracture system around the hydraulic fracture. This stimulation technique involves placing micro-sized proppant particles in the natural fracture system around the hydraulic fracture at the leak-off pressure condition in order to maintain the fracture systems’ conductivity during the post-fracturing production. The equations for one-dimensional suspension flow around and perpendicular to the hydraulic fracture, accounting for rock deformation and particle capture, have been derived. The effects of permeability reduction due to particle straining are incorporated in the analytical model. The laboratory tests on the solid-particle suspension injection into the natural fractures of a coal core at elevated pressures are successfully matched by the model. The experimental results confirm there is an optimum concentration of placed particles whereby a maximum permeability is retained; this optimal proppant particle placement yields nearly a three-fold increase in permeability. The analytical model has been tuned from these experiments to calculate the optimum concentration of placed particles and predict the productivity improvement after stimulation of the fracture system around the hydraulic fracture. A case study is presented to demonstrate the productivity enhancement by applying the proposed technique in a coal-bed-methane (CBM) reservoir. The laboratory-based analytical model predicts a six-fold increase in the productivity index. Examples for the possible practical applications of the developed technology in hydraulic fracturing or stimulation treatments in coals are also presented