Hydrodynamic Modeling of Single Well Chemical Tracer Test with Drift Fluid Due to Flooding on the Example of the Oil Field in Western Siberia

Chemical methods of enhanced oil recovery in general and Surfactant Polymer (SP) flooding, in particular, are considered as a promising tertiary method of developing mature oil fields in Western Siberia, with the potential to increase oil recovery to 60–70% of the initial geological reserves [1, 2]. The selected SP compositions were tested at one of the oil fields of Western Siberia in December 2022-January 2023 using Single Well Chemical Tracer Test. A total of three SWCTTs were conducted on three wells. The residual oil saturation after waterflooding (Sorw) was determined at the first stage of SWCTT. Then the surfactant-polymer composition was injected into the well and pushed by water chase. After that the residual oil saturation after chemical flooding (Sorc) was determined. The effectiveness of surfactant-polymer flooding was defined as the difference between Sorw and Sorc. Initial analysis of SWCTT results showed low efficiency of surfactant-polymer flooding, because Sor is calculated using the well-known analytical formula [3], which is applicable for ideal conditions (radial flow of tracers to the well). As it was shown in [4] the shape of tracer production curves can be affected by the drift (displacement) of the fluid front due to the pressure gradient between the zones of fluid injection and withdrawal, which significantly complicates the interpretation and modeling of the results. The surrounding wells stock analysis showed that the target well was heavily influenced by neighboring injection and production wells, so fluid migration in the reservoir must be accounted for in order to correctly analyze the results. Considering the fluid drift in the reservoir during SWCTT modeling allowed us to correctly adapt the tracer production curves and correctly estimate the efficiency of surfactant-polymer flooding. Without taking drift into account, the difference between Sorw and Sorc was 0.07, which corresponds to an increment of oil residual factor (ΔRF) of 11% OOIP (original oil in place). SWCTT modeling considering drift showed that the real efficiency of surfactant-polymer flooding was: ΔSorc = 0.115, which corresponds to ΔRF of 17.4% OOIP. Thus, SWCTT modeling with consideration of drift showed that the applied surfactant-polymer composition is a highly effective oil displacing agent.