Gas Tracer Transport - Correct Formulation and Fast Post-Processing Simulation Technique.

Abstract

Abstract This paper describes a fast post-processing method for simulating gas tracer transport. The partitioning between phases is described by a convenient and correct formulation. Gas tracers (e.g. per-fluorinated or radio-labelled hydrocarbons) can be used to trace injection gas during secondary recovery, CO2-injection for CCS or EOR etc. Laboratory experiments show that commonly applied reservoir simulation methods for gas tracer transport should be improved. This paper highlights the effect of gas tracer partitioning between phases and presents a formulation that can be used in practical reservoir simulations. A fast post-processing tracer simulation technique is introduced to solve the gas tracer transport in real-field reservoir cases. The formulation of the solution exploits the fundamental assumption that tracers do not affect the phase transport. The partitioning of the tracer components is solved fully coupled with the tracer transport. The post-processing is based on previously solved reservoir simulation runs and gives significant savings in CPU-time. Using laboratory results for several gas tracers, we observe that models based on commonly applied tracer formulations, are unable to correctly handle the tracer partitioning between the gaseous and oleic phases, and that the formulation presented here resolves that problem. Using real-field reservoir simulation cases, we demonstrate the practical improvement achieved. Our main conclusion is that a correct description of gas tracer phase partitioning is important to enhance predictions from gas tracer tests. The paper contributes to improved and rapid gas tracer simulation, important for correct interpretation of gas tracer results from inter-well tracer tests in petroleum reservoirs. The formulation of the equation and the simulation techniques described is also valid for other applications, such as water tracers, CO2-sequestration, non-aqueous phase liquids etc.