Extension of Capacitance-Resistance Model to Tracer Flow for Determining Reservoir Properties

Abstract

Abstract Several tools and techniques exist to understand distributions of reservoir properties. Interwell tracer testing is one ofthe most common methods to obtain reservoir information from the amount of tracer produced. The capacitance-resistance model (CRM) is an analytical tool to estimate connectivity between producer-injector pairs from historical rates and (when available) bottom hole pressure data in waterfloods.Because the CRM is a physically based, simple input-output model, its combination with tracer testing can provide insight into reservoir features. To enable the CRM application to tracer flow, we incorporated tracer models,based on miscible displacement theory, into the CRM. Reservoir properties are estimated as a result of the model fitting to produced tracer data. In this paper, we present three tracer models:a dispersion-only(short range autocorrelation) model, a Koval (long-range) model, and a combination of the two. To incorporate the tracer models into the CRM, we used two methods, serial fitting (CRM then tracers) and simultaneous fitting (CRM and tracers). We applied these techniques to tracer data from 10 injectors and 10 producers of the Lawrence field. Results suggest that interwell connectivity obtained from the CRM is in good agreement with the observed peak tracer concentrations. All tracer models are able to give a good fit in most of the cases. Comparing among the tracer models, the combined model can better represent a tracer flow than the other two models alone. We also found that the simultaneous fitting method gives the best fit to total producer rate data and tracer data. Simultaneous fitting mitigates the non-uniqueness of the fits, leading to an improvement of tracer matching. The reservoir properties obtained in this study (Koval factor and dispersion coefficient) were also analyzed and compared to those from previous measurements.