试论近临界凝析气在PVT筒中的分层现象

A discussion on the layering of near critical gas condensate in PVT cell.

我国西部不断发现高含凝析油凝析气藏和近临界凝析气藏，详细了解这类气藏的特殊性质和相变特征不仅具有科学价值，而且是开发研究的重要基础。在研究近临界凝析气流体的高压物性实验中，可观察到压力缓慢降低接近露点压力时，ＰＶＴ筒中单相凝析气出现一系列红色流体层。由于近临界流体等温压缩性大和重力的影响，凝析气流体中存在较大的密度梯度，ＰＶＴ筒中这种颜色分层是流体密度梯度涨落而造成的光的散射现象，甚至产生“临界乳光”现象，这种光学现象是凝析气流体在近临界区域所具有的共性。近临界两相流体过渡带区域较宽，密度涨落显著，流体体系很难在短时间建立平衡状态，如果在高度不大的ＰＶＴ筒中流体呈现十分明显的颜色分层现象，说明该流体必然具有近临界特性，可以通过观察流体分层现象随压力变化而产生的变化来判断流体的相态特征。图２参７（郭海莉摘）

More near critical gas condensate fluids are to be discovered with increase in depth of reservoir. A thorough knowledge of this kind of fluid is not only of scientific values, but also a foundation of field development. The experimental measurement in PVT cell is still a necessary means of obtaining the properties of fluids. The phase transformation of fluid is often observed through the physical phenomena in PVT cell. The near critical gas condensate has many particular properties: the density variation with height of monophase fluid is very evident; in two phase region, a large transient region may exist between gas and condensate instead of a distinguishable interface. During the experimental process, a series of red layers often appear progressively. Then the color vanishes gradually with decrease in pressure in the upper and lower parts of the cell. The density gradient of near critical gas condensate in PVT cell is demonstrated in this paper. According to the optical theory, the red layering phenomena of near critical gas condensate in PVT cell during phase transition is discussed in detail so as to provide guidelines for later study of gas condensate. Subject