Enhanced condensate recovery using CO₂ dump flood

Abstract

In order to increase condensate recovery from a gas-condensate reservoir, one may inject gas to increase the reservoir pressure to avoid condensate dropout in the reservoir. Several types of gas may be chosen for this process. However, two commonly used are CO₂ or CH₄. Injecting CO₂ or CH₄ will not only increase the reservoir pressure but also decrease the dewpoint pressure, making it more difficult for gas to condense into condensate when the pressure in the reservoir declines as a result of gas production. In the Gulf of Thailand, many gas fields are multi-stacked reservoirs. Some of these reservoirs have high CO₂ content. It is not economical to produce gas from these reservoirs. One way to make use of this high-pressure gas is to perform internal dump flood in which high CO₂ gas is flowed from the source reservoir to the target gas-condensate reservoir to increase the pressure of the target reservoir as well as to reduce the dewpoint of the reservoir fluid. The main purpose is to increase condensate recovery by preventing condensate dropout in the reservoir. In this thesis, hypothetical reservoir models were created in order to evaluate the performance of gas dump flood. Three important variables which are timing of the flooding, composition of the source gas, and the difference in original depths of the source and target reservoirs were considered in this study. The results from reservoir simulation show that the best time to start gas dump flood is before the reservoir pressure drops below the dewpoint pressure and that the composition of the source gas and the difference in original reservoir depths have a slight effect on the recovery of condensate.