Deep Green

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    Physical interpretation of interwell partitioning tracer tests for estimation of remaining oil saturation in layered carbonate reservoirs
    (2025) Fontalvo, Samuel D.; Yutkin, Maxim P.; Hassanizadeh, S. Majid; Radke, Clayton J.; Patzek, Tadeusz W.
    Interwell partitioning tracer tests (IPTTs) are conducted in mature oil fields to estimate remaining oil in place, which is crucial for subsequent economic analyses and decisions regarding further field development. An IPTT involves the simultaneous injection of two types of tracers: conservative and partitioning, that probe the aqueous and oil phases, respectively. Although this test requires time, it probes the entire fluid flow path, not just the near-wellbore area, as is the case with other methods such as single-well tests. Accurate interpretation of interwell tracer test data is of critical importance for the oil and gas industry. Published IPTT case studies lack physical justification for the choice of tracer flow models. In this study, we provide such justifications along with guidelines for selecting appropriate tracer flow models. First, we review existing models for the transport of partitioning and conservative tracers and demonstrate their applicability range based on mass conservation analysis. Based on this analysis, we propose a refined model of partitioning tracer flow with Robin boundary conditions that accounts for non-equilibrium partitioning. Such analysis is missing in the literature. Next, we illustrate errors in estimating remaining oil if an inappropriate model is used for data interpretation. Notably, the choice of an incorrect model can lead to either underestimation or overestimation of the remaining oil, with the latter being of greater financial concern. Finally, we apply the non-equilibrium partitioning model to a published IPTT dataset from a layered carbonate reservoir and compare our remaining oil estimates with results of the original study. To the best of our knowledge, analysis of such cases with non-equilibrium partitioning has not been documented in the literature.