Numerical investigation of fracturing fluid transport and storage during shale gas production: Where does fracturing fluid go?

Abstract

Shale gas has become a new worldwide focus in oil and gas exploration. The environmental problems brought by hydraulic fracturing technology are attracting increasing attention. Shale formations exhibit strong discontinuities, heterogeneity and anisotropy making the fracturing fluid transport process more complicated. To quantitatively identify the transport and storage characteristics of contaminant in fracturing fluid in the shale gas exploitation process, a DFN-EPM coupled model was established. The fracturing fluid flow field, the featured contaminant (2-BE) transport and storage situations were analyzed. Furthermore, the effects of Initial Shut-in Pressure and matrix porosity on transport and storage of 2-BE were investigated through two study-cases. Results indicate that more than 90% of the remaining 2-BE was stored in the matrix pores in most cases in this study. Furthermore, the higher the Initial Shut-in Pressure, the less the 2-BE content in the fracture during the hydraulic fracturing process, and the more 2-BE eventually enter the matrix pores. The greater ratio of the total 2-BE in the matrix at the final state occurred when the matrix porosity was higher. For instance, the ratio of 2-BE in the fractures of the model with matrix porosity of 0.05 was smallest, while the largest ratio of 2-BE in the matrix occurred. This study has important significance for the study of groundwater environmental pollution during shale gas exploitation.