As still deeper formations are drilled, gas condensates containing high carbon-number hydrocarbons which may precipitate during production and in the reservoir, are encountered. An increasing focus of attention on its phase behavior has been made worldwide in recent years. The main purpose of this paper is to investigate experimentally the characteristics of phase behavior of this new type of gas condensate systems with high wax content. Therefore, a series of experiments are carefully made for different GOR fluids, including constant composition expansions and the determination of wax deposition points. The separator gas and liquid are collected from the same producer and recombined in the laboratory to cover the ranges of GOR encountered in the field.
The results show that the quality lines of the highest GOR fluid in two-phase region are parallel to each other and terminated at the appearance of wax deposition. Thus the fluid has no convergence point, or critical point. It is also found that the biphase regions expand with the increase in GOR. In other words, gas injection may highly increases the saturation pressure locus contrary to the usual belief that the two-phase region will become smaller as more gas injected into the reservoir leads to more leanness of the reservoir fluid. Another interesting finding is that the more amounts the heavy hydrocarbons, the lower dew- & bubble- point pressures of the gas condensate systems used in this study. This is also contrary to the previous literature results that increasing amounts of heavy hydrocarbons increase the retrograde dew point pressure. Thus the deduced conclusion28 that a compositional gradient in the segregated fluids results in higher observed dew point pressures at the bottom of the fluid column, may not be made to the highly waxy gas condensate systems used in this study.
Additionally we also found the wax deposition temperature increased with decreasing GOR.