Acid pre-flushing evaluation before pH-sensitive microgel treatment in carbonate reservoirs: Experimental and numerical approach

Abstract

pH-sensitive microgel flooding is a deep conformance control technique in which the microgel viscosity depends on formation pH. Lowering the formation pH by an acid pre-flushing treatment guarantees easy injection of these microgels. The applications of these microgels were mainly dedicated to sandstones in the literature. However, this study provides an integrated laboratory and numerical modeling approach to find a proper pre-flushing acid in carbonates. The performance of various acids (strong and weak) is evaluated via batch experiments (static tests). The dynamic of acid pre-flushing (dynamic test) and pH-sensitive microgel injection are investigated by flooding experiments. A compositional reactive flow model (advection-diffusion-reaction), developed in Python, is also used to analyze the behavior of the flooding experiments. To evaluate the flooding performance, a 3-D field-scale reservoir simulation model with high-permeability contrast is then implemented. The batch and dynamic tests show that acetic acid can maintain a low-pH environment across the medium, which provides a favorable condition for pH-sensitive microgel transports. The geochemical model can accurately predict the measured equilibrium pH and calcium concentration of effluents at different injection rates and salinities. After the establishment of a near-equilibrium condition, the remaining unionized acids in the flooding experiments result in deep conformance control of pH-sensitive microgels. The pH-sensitive microgel flooding at the field-scale reveals an excellent performance in permeability modification of high-conductive zones. Plugging the first 30% of a high-permeable channel can guarantee the recovery factor increase of this deep conformance control technique.