The effect of supercritical CO₂ fracturing fluid retention-induced permeability alteration of tight oil reservoir

Supercritical CO₂ (SC-CO₂), as a non-aqueous material of fracturing fluid, receives widely attention in the development of unconventional reservoirs. In this study, permeability regain (K_rg) was introduced to characterize the permeability alteration on tight cores by SC-CO₂ fracturing fluid. Meanwhile, scanning electron microscope (SEM), microscope system, nuclear magnetic resonance (NMR) were used to reveal the mechanisms of permeability alteration at different scales. The results showed that the composition of SC-CO₂ fracturing fluid, fluid filter loss, and reservoir permeability were all responsible for permeability alteration. With the increasing thickener contents and filter loss of fracturing fluid, core permeability regains turned to be declined. Comparatively, tight cores which consist of more micro-nanometer sized pores were more likely to receive more formation damage of permeability, as well. The retention of thickener in microchannels (micro pores) were confirmed to be the main mechanisms on permeability alteration.