花场近临界油气藏流体相态和开采特征

Phase behavior of fluid and development characteristics of Huachang near-critical hydrocarbon reservoir

花场近临界油气藏具有以下特性:①在近临界区域,当地层压力低于泡点压力时,挥发油液相体积随压力的降低急剧减小;而地层压力低于露点压力时,凝析气反凝析液相体积会随压力的降低而急剧增大。②近临界油具有气油比、地层体积系数及收缩率高的特性。③近临界态油气藏井内静压梯度出现倒置的异常现象,即压力梯度自上而下降低;开始生产一段时间后,随着地层压力的不断下降,静压梯度曲线的形态也逐渐变化;当地层压力降至一定程度后,这种异常现象随即消失。④在开采过程中,近临界油气藏的生产气油比随地层压力的下降呈先下降后持续升高的现象,而常规凝析气藏的气油比随地层压力的下降持续升高。

Huachang near-critical hydrocarbon reservoir was characterized with its peculiar properties. In the near-critical region, the liquid volume steeply decreased with decreasing pressure for volatile oil and dramatically increased with decreasing pressure for gas condensate. The near-critical fluid has the features of high gas-to-oil ratio （GOR）, high formation pressure factor and high shrinkage factor. The static pressure gradient may exhibit inverse effect along the wellbore upside, which shows that the pressure gradient increases from bottom to top, which implies the heavier fluid floating on the lighter fluid. After some periods of production, the static pressure gradient curve changed continuously with the reservoir pressure decline. This inverse effect could disappear when the reservoir pressure dropped down to some extent. During the production period, when formation pressure decreased, the producing GOR decreased firstly and increased then in the near critical reservoirs, but, the producing GOR continuously increased in the normal gas condensate reservoirs.