Simulation-assisted gas tracer test study of Tarim Yaha gas-condensate reservoir in China

To enhance oil recovery and optimize a production plan, injected water or gas fluid should be monitored and tracked, which can be realized by gas tracer technology. Tracer test technology has become an effective method for evaluating the flow condition of reservoirs and estimate reservoir properties. Gas tracers, such as chemical and radioactive materials, have been used to identify well-to-well connectivity, reservoir heterogeneity, high-permeability pay zones, sweep efficiency, and residual oil saturation. Moreover, tracer tests have been used to evaluate well interference among multiple hydraulically fractured wells and qualitatively predict possible fracture geometries. Therefore, the accurate quantification of tracer transport is of great importance. However, theoretical study of gas tracers in a condensate gas reservoir has not been thoroughly conducted to date. Current tracer transport models mostly focus on the gas tracer flow in oil reservoirs and cannot be directly applied to condensate gas reservoirs. To the best of our knowledge, the application of a gas tracer to recycle gas injection in gas condensate reservoirs has not been thoroughly studied. In this paper, we propose a mathematical model to quantitatively describe the gas tracer transport mechanism in condensate gas reservoirs. Our mathematical model is based on the mass conservation law and is numerically solved via the Integral Finite Difference method. The results predicted by our model have been compared to and verified by real data collected from the field. The model has been used to optimize the recovery of the Yaha Condensate Gas Field in the Tarim Basin, China. With the assistance of our tracer transport model, the pressure drawdown speed of the Yaha field has been successfully slowed from 0.8 MPa/year to 0.5 MPa/year. Generally, this study not only provides key insights into the transport mechanism of gas tracers but also presents the application of numerical tools to guide the production of gas condensate reservoirs. The technique introduced in this study could be potentially extended to condensate oil production in other fields.