Bongkot South Field Multilayer Reservoirs Retrograde Gas Condensate Model

Abstract

Abstract BONGKOT South field is a multilayer retrograde gas condensate reservoirs field. The condensate –gas ratio (CGR) and condensate production forecasts are a major challenge of the field especially with monobore well completion which has limited zonal contribution data. This paper describes how the pressure-based CGR framework with integrated reservoir engineering data analysis is introduced to improve the forecast accuracy and enhance reservoir behavior intuition compared to the existing empirical methodology, CGR versus cumulative production. The framework adopts the pressure-based CGR correlation which can model the retrograde condensation while maintaining simplicity for practical use. The proposed framework is split into 2 sections. The producing CGR parameters are established through history matching with actual production data using integrated information to enhance intuition on the CGR behavior which improve the accuracy of the CGR matching and forecast. The non-producing CGR is estimated using the established CGR correlations which were constructed based on the sample with CVD analysis and all single reservoir production data. The estimated CGR then apply to the simulator result to get the condensate forecast. The forecasted field condensate rate during plateau period ranges between 8,000 to 11,000 STBD with single reservoir initial CGR and field average producing CGR varies in range of 15 – 120 STB/MMSCF and 17-28 STB/MMSCF respectively. Field blind test was also performed to validate the framework which shows mismatch in a total condensate volume of less than 3% over a total raw gas volume of 47 BSCF. Results from various well-level CGR history match show different CGR decline behaviors of retrograde gas condensation and vaporization at lower reservoir pressure. The matching of such behavior can be achieved by the proposed framework which adopts pressure-based correlation while the existing production based correlation cannot. The proposed framework has demonstrated that BONGKOT South operators can accurately predict well producing CGR for prudent reservoir management and development. Well-structured integrated data analysis during CGR history match provides better intuition into reservoir behavior which could guide engineer to better reservoir management decision. The established CGR trend could also be used by external optimizer module, e.g. LINOPT, as CGR decline input to better optimize the longer-term condensate recovery.