A one-spot EOR pilot was successfully completed to demonstrate the efficacy of a lab-optimized ASP formulation to mobilize remaining oil from a giant sandstone reservoir in Kuwait. This one-spot EOR pilot, which also referred to as a Single Well Chemical Tracer (SWCT) test, was a significant milestone in de-risking ASP flooding for multi-well pilot implementation.
The vertical zone of investigation for the Raudhatain Zubair (RAZU) SWCT was chosen to be a confined channel sand with relatively homogeneous and representative properties in a producer near the proposed pilot area. Two SWCT tests were performed and the difference in residual oil saturation from post water flood and post ASP injection tracer tests quantitatively determines the displacement efficiency of the ASP slug. The tracer chemicals for the tests included a hydrolyzing, partitioning tracer (ethyl acetate) and two alcohols (n-propyl alcohol and isopropyl alcohol) that serve as cover tracer and material balance tracer, respectively, to ensure robustness of test interpretation.
The water flood SWCT test showed ideal behavior with well-defined profiles. Interpretation of this test was accomplished using a single layer model and showed that at the end of the water flood, the residual oil saturation to water was 0.24 ± 0.02% in the 23 -ft interval for the SWCT test. The ASP tracer test was complicated due to poor injectivity, well mechanical issues, and dilution from a zone which did not accept any SWCT test injection fluids but contributed substantially to production. Due to the dilution from another zone, the ASP tracer test profiles were more dispersed than the water flood tracer test but were adequately modeled using a two-layer model with irreversible flow. Analysis of the ASP SWCT test showed that the average oil saturation was reduced to 0.06 ± 0.05%, which represents a ~67% reduction in residual oil saturation.
Despite poor injectivity leading to a reduced polymer drive and taper injection and dilution from another zone resulting in a non-idealized tracer response, careful interpretation of the SWCT test measurements resulted in a reliable estimate of the post-ASP oil saturation. The SWCT test results demonstrate the feasibility of applying ASP flooding to increase oil recovery from a giant high-temperature sandstone reservoir in North Kuwait.