抄録
Yufutsu gas condensate field has a fractured reservoir which consists of conglomerate and granite. It contains condensate-rich gas. We observed some strange fluid behaviors. Production gas oil ratio ranges from 900 m3/kl to 1,900 m3/kl according to production area where reservoir depth is different. Gas production started ten years ago. At the early stage of the production, gas oil ratio decreased with time. This trend is opposite from normal behavior of a gas condensate reservoir. Also, we observed that heavy gas existed on light gas in a tubing at a specific well.
In order to explain such strange phenomena, we introduced a thermal diffusion theory in 1999 and 2000 by a support of Japan National Oil Corporation (currently JOGMEC). The reservoir is approximately from 4,000 m to 5,000 m deep and 1,000 m thick. So, pressure and temperature are varying in a wide range with the reservoir depth. Gas compositions at the top and the bottom of the reservoir are so different that methane, the lightest component, tends to increase with depth and temperature due to the thermal diffusion effect, because methane has larger thermal diffusion coefficient than the other heavier gas components. We expect that this assumption could explain the strange fluid behaviors.
This paper reviews the above phenomena and the theory and reports current effort to increase condensate recovery using gas cycling scheme.
