Electrostatic Origins of CO2-Increased Hydrophilicity in Carbonate Reservoirs

Abstract

Injecting CO₂ into oil reservoirs appears to be cost-effective and environmentally friendly due to decreasing the use of chemicals and cutting back on the greenhouse gas emission released. However, there is a pressing need for new algorithms to characterize oil/brine/rock system wettability, thus better predict and manage CO₂ geological storage and enhanced oil recovery in oil reservoirs. We coupled surface complexation/CO₂ and calcite dissolution model, and accurately predicted measured oil-on-calcite contact angles in NaCl and CaCl₂ solutions with and without CO₂. Contact angles decreased in carbonated water indicating increased hydrophilicity under carbonation. Lowered salinity increased hydrophilicity as did Ca²⁺. Hydrophilicity correlates with independently calculated oil-calcite electrostatic bridging. The link between the two may be used to better implement CO₂ EOR in fields.