The residual oil saturation obtained from SWCTT is critical for designing enhanced oil recovery (EOR). However, a key assumption in conventional SWCTT is that only single phase (water) is mobile. In reality, this is often not the case, and significant error can occur if the conventional SWCTT analysis method is used when multiple phases flow at the same time. The objective of this study is to improve the accuracy and precision of SWCTT interpretation in multi-phase flow condition.
In this paper, we propose an innovative procedure of modified SWCTT and the method of moment (MoM), aiming at the two-mobile-phase condition. In the development of the algorithm, a ratio parameter is introduced to adjust the calculated swept volume difference between the conservative tracer and partitioning tracer. In addition, a mixture injection of oil and water is required, instead of pure water injection in SWCTT.
The proposed approach is verified through numerical simulation on synthetic cases with known input parameters. The simulated models consist of a radial flow regime with a single vertical well in the center. The input oil saturation varies from 0.1 (immobile oil saturation) to 0.9. Our results show that the saturation estimated from modified MoM matched the simulation input data, which indicates that our approach is able to capture the saturations under two-mobile-phase condition. Moreover, the modified MoM can also be applied in single-mobile-phase condition and improved accuracy of conventional MoM.