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

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.