Phase Behavior and Compression Factors of Ultradeep Condensate and Dry Gas Reservoir under High Temperature and Pressure: Experiment and Calculation

Abstract

The exploration and development of ultradeep gas reservoirs have advanced significantly over the past 10 years, making these resources a crucial component of proved reserves. Understanding the phase behavior of reservoir fluids under ultradeep conditions is essential for designing and optimizing development schemes, especially given the extreme temperatures and pressures. However, existing empirical correlations and thermodynamic models often fall short of accuracy under these ultrahigh-pressure conditions. In this study, three ultradeep gas samples were analyzed using constant-composition expansion experiments. The compression factors and phase behavior properties at five groups of reservoir temperatures were obtained, with the highest pressure reaching 146 MPa. The experimental results show that the dew-point pressure and maximum retrograded liquid amount decrease with increasing temperature, while the compression factors increase with pressure. Meanwhile, a thermodynamic model based on the Soave–Redlich–Kwong equation of state was developed to precisely describe the compression factor. The capabilities of four empirical correlations and the Groupe Européen de Recherches Gazières model were investigated and compared. The results show that the improved thermodynamic model in this work demonstrated superior accuracy under ultradeep conditions, reducing the average absolute deviations for compression factors from 2.42% with the original equation of state to 0.52%.