Pressure Transient Analysis for the Fractured Gas Condensate Reservoir

Abstract

Gas condensate reservoirs exhibit complex thermodynamic behaviors when the reservoir pressure is below the dew point pressure, leading to a condensate bank being created inside the reservoir, including gas and oil condensation. Due to natural fractures and multi-phase flows in fractured gas condensate reservoirs, there can be an erroneous interpretation of pressure-transient data using traditional multi-phase models or a fractured model alone. This paper establishes an analytical model for a well test analysis in a gas condensate reservoir with natural fractures. A three-region composite model was employed to characterize the multi-phase flow of retrograde condensation, and the fractured formation was described by a dual-porosity medium. In the first region, both the gas and condensate phases were mobile. In the second region, the gas was mobile whereas the condensates were immobile. In the third region, the only moving phase was the gas phase. The analytical solution was solved by a Laplace transformation to change the partial differential equations to ordinary differential equations. The Stehfest numerical inversion technique was then used to convert the solution of the proposed model into real space. Subsequently, the type curve was obtained and six flow regimes were determined. The influence of several factors on the pressure performance were studied by a sensitivity analysis. Finally, the accuracy of the model was verified by a case study. The model analysis results were in good agreement with the actual formation data. The proposed model provides a few insights toward the production behavior of fractured gas condensate reservoirs, and can be used to evaluate the productivity of such reservoirs.