Swelling of Shales with Slickwater in Carbon Dioxide

Usage of shale gas as an energy source offers additional reassurance if fossil fuels become depleted. Because the shale reservoir is buried deep, the formation has the characteristic of high ground stress, high elevated temperatures, and high horizontal stress difference. As a result, the fracture propagation direction is characterized as single with unsatisfactory stimulated reservoir volume. The unsatisfactory stimulated reservoir volume modification conditions of the shale gas reservoir’s self-storage will result in low production and poor economic effects. It has forced researchers to look for other ways, such as implementing supercritical CO2 as a prefluid. However, the strain of shale (containing slickwater) caused by CO2 injection and the presence of CO2 inside the reservoir should be taken into account in industrial applications. To this end, three kinds of experiments were performed in this study to investigate the shale strain caused by gas. In this regard, the main mechanical characteristics of the reservoir were measured for the samples with and without slickwater treatment. Meanwhile, the CO2-induced swelling and helium-induced strains were analyzed at 353 K and 0–20 MPa. After the slickwater treatment, the shale elastic modulus decreased. The Biot coefficient of the shale increased and substantially changed the gas-pressure-induced strain. Slickwater significantly reduced the CO2-induced swelling by ∼50%.