Biogeochemistry during hydraulic fracturing: A critical review of reservoirs, fluids, processes, and implications

The hydraulic fracturing process disrupts the pre-existing equilibrium among water, rock, gas, and microbe in deep subsurface environments. This process shapes a novel microbial ecosystem and triggers a series of complex biogeochemical interactions, thereby influencing natural gas recovery efficiency and flowback water quality. This review critically examines biogeochemical processes during hydraulic fracturing in three prevalent low-permeability reservoirs: tight sandstone, shale, and coal reservoirs, aiming to generate biogeochemical insights into environmentally sustainable unconventional energy exploitation. Building on the examination of low-permeability reservoirs and fracturing fluid characteristics, the discussion delved into biogeochemical processes, encompassing fluids mixing, mineral dissolution and precipitation, clay swelling, ion exchange and adsorption, and biochemical reactions. These interactions involve intricate and coupled physical, chemical, and biological processes, further complicated by the heterogeneity of reservoirs and the complexity of fracturing fluid compositions. Biogeochemistry persists throughout the lifecycle of unconventional hydrocarbon extraction, impacting energy recovery, flowback fluids water quality, and environmental outcomes. Optimizing fracturing fluids additives based on biogeochemical insights can minimize contaminants and enhance production efficiency. This study offers in-depth insights into water-rock interactions and microbial activities in deep formation, highlighting the nuanced effects of biogeochemical processes on hydraulic fracturing and its environmental impact. It underscores the importance of refining hydraulic fracturing designs to enhance unconventional gas production while reducing environmental risks.