WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

Abstract

Hydraulic fracturing is widely applied to economical gas production from shale reservoirs. Still, the gradual swelling of the clay micro/nanopores due to retained fluid from hydraulic fracturing causes a gradual reduction of gas production. Four different gas-bearing shale samples were investigated to quantify the expected shale swelling due to hydraulic fracturing. These shale samples were subject to heated deionized (DI) water at 100°C temperature and 1.2 MPa pressure in a laboratory reactor for 72 hours to simulate shale softening. The low-temperature nitrogen adsorption and density measurements were performed on the original and treated shale to determine the micro and nanopore structure change. The micro and nanopore structures changed during shale swelling, and the porosity decreased after shale treatment. The porosity decreased by 4% for clayey shale, while for well-cemented shale the porosity only decreased by 0.52%. The findings showed that the initial mineralogical composition of shale plays a significant role in the swelling of micro and nanopores and the pore structure alteration due to retained fluid from hydraulic fracturing. A pore network model was used to compare the permeability due to shale softening. The permeability results show a reduction from 3.76E-16 m2 to 2.62E-17 m2 after treatment based on the simulations.