Investigation of Oxidative Dissolution and Mineral Swelling Effects on Seepage Channels and Permeability of Calcareous Shale Reservoirs: An Experimental Study

Abstract

Multistaged hydraulic fracturing of a horizontal well may significantly improve the permeability of the calcareous shale reservoir, but hard to improve the transport capacity of gas in nanopores, resulting in insufficient gas supply from the shale matrix to fractures and rapid production decline after the stimulation. Nevertheless, the seepage capacity and production will increase due to the water-rock interaction during the soaking process after fracturing. Our research proposes to utilize the reaction between persulfate and calcareous shale to strengthen the water-rock interaction, achieving oxidative dissolution and swelling. Ammonium persulfate was selected as the fracturing fluid additive to analyze the effect of oxidative dissolution and swelling on the macroscopic and microscopic seepage capacity of calcareous shale through technical means such as stress sensitivity test, NMR, and SEM. We conclude that persulfate’s oxidative dissolution and swelling will greatly promote fractures and increase permeability in calcareous shale reservoirs to reconstruct the seepage channels. The findings of this study have implications for determining and optimizing the fracturing fluid’s performance and the postfracturing production management system to develop calcareous shale reservoirs in a green and efficient manner.