Alteration of Bakken reservoir rock during CO2-based fracturing-An autoclave reaction experiment

When exposed to sc-CO2 only, changes observed include etching of the calcite grain surface and precipitation of salt crystals (halite and anhydrite) due to evaporation of residual pore water into the sc-CO2 phase. Dolomite and feldspars remained intact, and pyrite grains were slightly altered. Mercury intrusion capillary pressure (MICP) tests on reacted and unreacted samples show an increase in porosity when an aqueous phase is present but no overall porosity change with sc-CO2. The results also show an increase in permeability for brine-reacted samples.