Brine incompatibility is an intricate issue overshadowing the success of water-alternating-gas (WAG) enhanced oil recovery (EOR) project. Its effect is especially noted in uncontrolled Low salinity (Lowsal) waterflood-operated fields. In this study, the inefficient waterflooding in a low permeable Morrowan sandstone is investigated through a comprehensive experimental study. The implications concluded from this study are critical for improving the efficiency of CO2-WAG EOR and Sequestration with compatible brine injection. This in part was conducted through Core-flood experiments, fluid-fluid surface charge, compatibility, and rock-fluid interactions analysis. Stable electrostatic forces prevent in a solution prevents particle aggregation, but distortion in surface charges weakens the expulsion forces and causes precipitation. Surface charge and compatibility tests revealed fluid-fluid reactivity and scale formation influenced by high ionic concentrations differences, temperature, and pressure. Fluid-fluid mixtures with produced water exhibited a unique compatibility signature, with a transition point causing of increasing and decreasing turbidity and vice-versa for ζ-potential (zeta potential) respectively. Geochemical analysis indicated precipitation of aragonite, calcite, and dolomite under reservoir conditions. Rocks interacted differently with synthetic brine, showing intense surface activity with low salinity water. Element-mineral associations showed clays and mineral particles obstructing pores and pore throats. In summary, the principal mechanisms of waterflood failure include low permeability, mineral composition (especially clay minerals), clay mineral reactivity, increased pressure drop (ΔP), fluid-fluid reactivity. These factors collectively contribute to formation damage, pore plugging, reduced flow capacity, and ultimately the failure of waterflood operations. This study thus, provide a new dataset from a Morrowan-aged clastic reservoir in the Anadarko basin offering insights into waterflood response. This knowledge will aid in optimizing brine composition for CO2-WAG EOR or an informed decision on the type of improved recovery to employ.
Keywords: Inefficient waterflood, uncontrolled salinity, surface charge geochemistry, low permeability, zeta potential, electrical conductivity, Morrowan sandstone-Farnsworth Unit.
