Production data analysis of gas condensate reservoirs using two-phase viscosity and two-phase compressibility

Abstract

Due to the occurrence of multi-phase flow in gas condensate reservoirs, production data of such reservoirs cannot be accurately analyzed using single-phase, dry gas models. In this work, we established a new semi-analytical method for rate-transient analysis of gas condensate reservoirs producing during boundary-dominated flow. In particular, the single-phase flow assumption in the development of the material-balance pseudotime function for dry gas reservoirs is alleviated by incorporating two-phase viscosity and two-phase compressibility into a modified two-phase pseudotime function. Introducing the definition of two-phase pseudotime achieves the goal of (approximately) linearizing the governing diffusivity equation. Using the principle of superposition applied to the constant rate solution, this methodology is extended for wells with dynamic changes in well operating conditions (i.e. rates and pressures).Original gas-in-place (OGIP) can also be quantified through a specialized plotting technique. To validate the developed method, synthetic production data using fine grid compositional simulations for both lean and rich gas condensate fluids are analyzed. In all cases, the proposed approach provides reasonable estimates of simulator input reservoir properties (e.g. OGIP). The presented technique is successfully applied to the analysis of field cases. This work provides a practical and simple engineering workflow for production data analysis of conventional gas condensate reservoirs with multi-phase flow during boundary-dominated flow.