A N EW PRODUCTION DECLINE ANALYSIS MODEL FOR GAS/CONDENSATE RESERVOIRS

Inexpensive production data could be analyzed using well-defined production analysis models to estimate reservoir properties just like expensive pressure transient tests. Due to different thermodynamic behavior and multi-phase flow of gas/condensate reservoirs, production data of such reservoirs cannot be accurately analyzed using single-phase dry gas models. This study presents a novel analytical model to analyze gas/condensate production data. The developedmodel could estimate initial gas-in-place, average reservoir pressure, drainage area size, reservoir permeability, and well skin. For this purpose, the governing flow equation of multi-phase gas/condensate reservoirs was derived and linearized using new two-phase pseudo-functions and the boundary dominated flow solution was developed for variable bottom-hole pressure/rate conditions. The new equation is coupled with a material balance equation and forms a new production model. The proposed method forms a linear plot so that by using its slope and intercept, the desired estimates of reservoir properties could be determined. Also by introducing new dimensionless parameters, the obtained production model is presented in type curve analysis format. The proposed model is validated by different fine-grid compositional simulation models by changingtheir properties including different reservoir fluid types, relative permeability data, and production history mode. Results of this study are compared with the results of numerical models and error analyses are performed. Results show that the proposed method estimates the reservoir properties quite well for all models and all errors are within engineering practices.

Keywords:

Two-phase pseudo-function , Gas , condensate , Type curve , Boundary dominated flow