Measuring Partitioning Coefficients for Gas Tracer Mass Balance and Gas Injection Allocation

Abstract

An interwell gas tracer test provides very useful information not only to improve reservoir description but also to characterize flow dynamics. Approaches to tracer application can range from conventional qualitative interpretation to quantitative analysis including numerical simulation. Our aim is to optimize miscible gas injection efficiency by correct calculation of gas injection allocation based on mass balance of the injected tracer (how much of an injected tracer is produced in the various production wells). Since perfluorocarbon gas tracers are partitioning tracers, and the capillary tube sampling technique only allows measurement of tracer concentration in the gas phase, knowledge of the partitioning coefficient (Kd) of the gas tracers at sampling conditions (wellhead pressure and temperature) is required. We successfully developed and implemented experimental design, equipment set up and procedures to measure a set of consistent Kd values for the oil and the gas mix for all commercial available gas tracers. Subsequently, we integrated the Kd values with tracer and production data and estimated the correct recovery of the gas tracers. The next step was to estimate the gas injection allocation to optimize gas injection patterns and to provide input for improving the simulation history match. Our approach is a further step in quantitative analysis of tracer data and can be applied to provide valuable information to optimize gas injection and oil production.