M. Mercado and B. Martinez, PEMEX, M. Asadi, SPE, ProTechnics, and D.R. Casas, SPE, O’Jeito S.A. de C.V.
A gas interwell tracer program was designed and implemented to characterize the flow stream within the current injection/production pattern of the central part of the Mesozoic Chiapas-Tabasco Basin. The field includes one injector and four producers. Due to production, the average reservoir pressure fell and approached the dew point at reservoir conditions. Natural gas was injected to maintain reservoir pressure and optimize condensate production. A chemical interwell tracer was also injected to detect and evaluate the magnitude of any communication between the injection and production wells and to track the areal flow pattern within the field. The study was designed for 18 months and commenced in December 2000 and terminated in mid 2002. The results from the sample analyses provided information on the magnitude of highly permeable channels between the injector and producers as well as flow patterns within the field. Furthermore, the results provided valuable information on breakthrough time and fluid travel time. Sampling discontinued for over a year. In late 2003, it was decided to collect more samples from the same four production wells as well as one of the offset wells. The new sample analysis results indicated tracer concentrations at high levels from all of the wells except one. Based on these new results, a new sweep efficiency and total volume swept between the injection and production wells were calculated and are presented. Finally, an overview of formation heterogeneity, based on the three years interwell tracer study, is presented.