Depletion performance of gas condensate reservoirs is highly influenced by changes in fluid composition below the dew point. Long-term prediction of condensate gas reservoir behavior is therefore difficult due to the complexity of both composition variation and two-phase flow effects. In this paper, an integrated model was developed to simulate gas-condensate reservoir behavior. The model couples the compositional material balance or the generalized material balance equations for reservoir behavior, the two-phase pseudo integral pressure for near wellbore behavior, and outflow correlations for wellbore behavior.
An optimization algorithm was also used with the integrated model so it can be utilized in history matching mode to estimate original gas in-place, original oil in-place and productivity index parameters for gas condensate reservoirs. The model can be used to predict the production performance for variable tubing-head pressure and variable production rate. The model runs fast and requires minimum input.
The developed model was validated using different simulation cases generated with a commercial reservoir simulator for variant reservoir and well conditions. The results show a good agreement between the simulation cases and the integrated model. After validating the integrated model against the simulated cases, the model was used to analyze production data for a rich gas condensate field (initial CGR of 180 bbl/MMscf). Tubing head pressure data for four wells was used along with basic reservoir and production data to obtain original fluids in place and productivity indexes of the wells. The estimated parameters were then used to forecast the gas and condensate production above and below the dew point. The model is also capable to predict reservoir pressure and bottom-hole flowing and tubing head pressures and can account for completion changes when they occur.