A New Method To Predict the Performance of Gas-Condensate Reservoirs

Abstract

Summary Gas-condensate reservoirs differ from dry-gas reservoirs. The understanding of phase and fluid flow-behavior relationships is essential if we want to make accurate engineering computations for gas-condensate systems. Condensate dropout occurs in the reservoir as the pressure falls below the dewpoint, resulting in significant gas-phase production decreases. The goal of this study is to understand the multiphase-flow behavior in gas-condensate reservoirs and, in particular, to focus on estimating gas-condensate-well deliverability. Our new method analytically generates the inflow-performance-relationship (IPR) curves of gas-condensate wells by incorporating the effect of condensate banking as the pressure near the wellbore drops below the dewpoint. The only information needed to generate the IPR is the rock relative permeability data and a constant-composition-expansion (CCE) experiment. We have developed a concept of critical oil saturation near the wellbore by simulating both lean and rich condensate reservoirs and have observed that the loss in productivity caused by condensate accumulation can be closely tied to critical saturation. We are able to reasonably estimate re-evaporation of liquid accumulation by knowing the CCE data. We validated our new method by comparing our analytical results with fine-scale-radial-simulation-model results. We demonstrated that our analytical tool can predict the IPR curve as a function of reservoir pressure. We also developed a method for generating an IPR curve with field data and demonstrated its application with field data. The method is easy to use and can be implemented quickly. Another advantage of this method is that it does not require the knowledge of accurate production data including the varying condensate/gas ratio (CGR).