Study on High-Pressure Treatment of Unconventional Reservoirs with Water-Based Fluids

Shales are tight rocks with ultra-low porosity and often contain hydrocarbons (oil and gas). Both the United States and Israel have abundant shale formations containing oil and gas. The majority of shale hydrocarbon production in the United States takes place in Permian basin, Texas, whereas the largest kerogen shale deposits in Israel occur in the Negev area. For the recovery of oil and gas, shale formations are hydraulically fractured by injecting water-based fluids under high pressure. To transition away from fossil fuel use and address atmospheric greenhouse gas levels, sequestration of carbon dioxide (CO₂) and hydrogen (H₂) storage is now proposed in depleted tight hydrocarbon formations, such as shales. Shales are composed largely of clays and silts, bound by carbonates to form ultra-tight matrices, and containing interconnected nano- to micro- to macro-voids with total porosities of 1-6%. The introduction of fracturing fluids and, potentially, other fluids for storage purposes (e.g., CO₂ and H₂) may cause changes to the ultra-tight shale matrix, as formations had previously been isolated for millions of years. These changes have been linked to reduced production of oil and gas and may affect possible storage of CO₂ and H₂. The interaction between artificially introduced fluids and shale formations, leading to softened shale, is attributed to the interlayer expansion of clays and the dissolution of cementing carbonates. This study seeks to investigate of the effects of interaction between various fluids and unconventional reservoir rock at high temperature and pressure for geo-storage implications.