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Improved Method of Moment To Determine Mobile-Phase Saturations Using a Single-Well Chemical-Tracer Test


 The single-well chemical-tracer test (SWCTT) has been applied for decades with much success in estimating residual oil saturation in near-wellbore locations. The information obtained from an SWCTT is critical for designing a method for enhanced oil recovery (EOR). However, a key assumption in the 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 a multiphase-flow condition.
 In this paper, we propose an innovative procedure of SWCTT and modify 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 the partitioning tracer. In addition, a mixture injection of oil and water is required, instead of the pure-water injection in an SWCTT.
 The proposed approach is verified through numerical simulation on synthetic cases with known input parameters. The model being simulated consists 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 the modified MOM matched the simulation input data, indicating 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 can improve the accuracy of conventional MOM.