An Anisotropic Permeability Model for Shale Gas Recovery Considering Slippage Effect and Embedded Proppants

Hydraulic fracturing has been widely adopted to improve shale gas recovery. A main issue in the implementation of hydraulic fracturing techniques is that proppants made from a variety of materials are normally introduced for the purpose of permeability enhancement. An embedded proppant can significantly alter the original gas flow behavior of shale, which should be taken into account when estimating shale permeability. In this paper, we propose a shale anisotropic permeability model that considers the effect of proppant embedding. Moreover, because the slippage factor is usually not fixed owing to the combined effect of proppant embeddings, any adsorption-induced swelling and stress, a slippage factor formulation is developed to consider the embedded proppant. Finally, an improved shale anisotropic permeability model that considers the combined effect of proppants and slippage is proposed. The validity of the model presented in this paper was assessed by comparing the results with previous experiments, and good agreement was found for the proposed model. The developed model can estimate accurately shale anisotropic permeability, when both the proppant and slippage effect are considered, and can be used to study related problems in the recovery of shale gas resources.