Produced water management and scale mineral control are important topics in hydraulic fracturing for shale hydrocarbon production. The rock-fluid interactions affect the produced water chemistry and scale mineral precipitation within the reservoir. Different shale mineralogy and hydraulic fracturing fluid (HFF) compositions will result in different rock-fluid interactions, thus influencing the fluid chemistry, scale mineral types and extent of impact. In this study, clay-rich Wolfcamp shale, carbonate-rich Wolfcamp shale, and clay-rich Marcellus shale cores were reacted with HFF in a flow-through experimental system at elevated temperature and pressure relevant to reservoir conditions. The HFF used in these tests were representative of formulations used in each formation. The influent and effluent chemistry of the three experiment groups were analyzed and compared. Small amounts of Ca-phosphates and Fe oxides/chromates were found in both Wolfcamp shale reaction experiments. Significant amounts of barite precipitates were found on the reactive surface of the Marcellus shale. The types of the precipitates observed in the reacted cores were consistent with the mineral saturation indices calculated based on the fluid chemistry.
Rock-fluid interactions have a great impact on the fluid chemistry and scale mineral precipitation during hydraulic fracturing in shale formations. Depending on the mineralogy of the shale formation and the chemistry of the injected hydraulic fracturing fluid (HFF), mineral dissolution and precipitation could vary significantly, leading to different produced water chemistry and alteration of the shale. The Hydraulic Fracture Test Site 1 (HFTS 1) is a field-based hydraulic fracturing research experiment performed in the Wolfcamp Formation in the West Texas Permian (Midland) Basin (Ciezobka et al. 2018). The HFTS project obtained core samples from wells drilled through the stimulated region (Ciezobka and Reeves 2021, Gale et al. 2018). Laboratory flow-through experiments were performed with clay-rich and carbonate-rich Wolfcamp shale cores from the HFTS project with synthetic HFF relevant to the site as part of the U.S. Department of Energy Multiscale Modeling Project (Birkholzer et al. 2021).
