Production forecasting of gas condensate well considering fluid phase behavior in the reservoir and wellbore

Abstract

Retrograde condensation occurs when the reservoir pressure falls below the dew point pressure in gas condensate reservoirs. Complex fluid phase behavior in the reservoir and the wellbore makes it challenging to predict the productivity of gas condensate wells. To date, the gas rate in the deliverability equation of gas well is assumed the gas rate at surface condition converted from that at the reservoir condition by using the volume factor. However, because of the complex fluid phase behavior in gas condensate wells, the gas rate at the reservoir condition cannot be directly changed to that at surface condition by using volume factor. Hence, the development of a new analytical model to accurately calculate the productivity of gas condensate wells is still required and necessary.In this work, we propose a new deliverability equation of gas condensate wells with a consideration of fluid phase behavior in both the reservoir and the wellbore. Also, several pseudo-pressure functions for different condensate distribution and flow models are examined systematically; these include the model before condensation, the model after condensation, but without condensate flow, the model after condensation and with condensate flow, and the model after re-vaporization. Two synthetic numerical simulation cases and two field case studies are performed to validate these deliverability equations for gas condensate wells.Results show that the phase behavior of gas condensate fluid in the wellbore plays a significant role in the deliverability evaluation and in the forecasting of gas condensate wells. If neglecting its effect on the deliverability, gas and condensate production rates could not be accurately predicted. The data from the proposed model have good agreement with the simulation and field production data of wells in Yakela Gas Condensate Reservoir and Yaha Gas Condensate Reservoir in China. If the conventional deliverability equation neglecting the effect of phase behavior in the wellbore was used, the predicted gas production will be higher than the actual value; even 50% higher than the actual value at high flow rates. Through these case studies, it can be concluded that the effect of condensate-gas phase behavior in the wellbore cannot be ignored in the deliverability equation for gas condensate wells.This work can provide a more accurate method of forecasting the gas and condensate production for condensate gas reservoirs and also guide optimization of single well production rate and gas recovery rate for gas condensate reservoirs.