Horizontal permeability anisotropy: Effect upon the evaluation and design of primary and secondary hydraulic fracture treatments in tight gas reservoirs

Numerous field trials have shown that fracturing and refracturing of tight sands have improved the economics of gas production from these reservoirs. In order to evaluate and design hydraulic stimulation in these reservoirs, it is essential to implement a holistic approach in which conducting a secondary fracture treatment after a primary production period from an initial hydraulic fracture is considered as an option. In such an approach, the optimal design is determined based on the combined performance of primary and secondary hydraulic fractures. In this paper we show that horizontal permeability anisotropy significantly affects productivity of both fracture and refracture as well as the potential length of a re-oriented secondary fracture and the optimal time for refracture treatment. For this purpose a numerical model is used to simulate fully coupled gas flow and stress changes from a hydraulically fractured and refractured tight gas reservoir. Results of this study have shown that horizontal permeability anisotropy is a key parameter in the holistic design of hydraulic fracture treatment. In particular, results of this study show that refracture treatment has a high potential to increase production when parallel component of horizontal permeability to the primary fracture is greater than the orthogonal component. We have also shown that horizontal permeability anisotropy controls the optimal time for conducting refracture treatment. (C) 2010 Published by Elsevier B.V.