Enhanced condensate recovery via gas dumpflood from multiple high CO2 gas reservoirs

Abstract

In the Gulf of Thailand, many gas fields are multi-stack gas condensate and dry gas reservoirs. Some of these dry gas reservoirs are not economically produced because of high CO2 content. However, these reservoirs can be used to perform gas dumpflood into a gas-condensate reservoir instead of gas injection to enhance condensate recovery due to much lower cost. In this study, a hypothetical reservoir model consisting of a gas-condensate reservoir with four thin-layered high CO2 gas reservoirs having typical properties found in the Gulf of Thailand was created using compositional reservoir simulation software in order to investigate the performance of the proposed method. This simulation study found that gas dumpflood can increase condensate recovery up to 17.5% over natural depletion scenario depending on several parameters. Although its recovery is lower than that of conventional gas injection, gas dumpflood is an attractive alternative due to lower cost. The important parameter is the fluid composition in the gas condensate reservoir. The rich gas condensate yielding higher condensate to gas ratio is more favorable for gas dumpflood from high CO2 source gas reservoir. On the contrary, for lean condensate, excessive amount of dumped source gas results in a large reduction of condensate recovery. The amount of CO2 should be limited in this case. Regarding perforation of the high CO2 source gas reservoirs, different sequences result in similar gas and condensate recovery as long as the same amount of total original gas in place is present in those perforated layers.