Investigation on the condensate gas composition variation and wax deposition mechanism during temperature-induced phase transition process

Abstract

To explore the impact of temperature changes on the wax precipitation of gas condensate during the ultra-deep condensate reservoir development, this work prepares condensate samples and creates the wellbore environment by using a PVT system. At the reference wellbore pressure, the carbon number distribution of components in condensate samples extracted under different temperature conditions is analyzed, and the proportion and composition of precipitated wax are further characterized. The results indicate that the gaseous condensate system gradually produces liquid oil as the temperature decreases. During this process, the precipitated wax particles aggregate while transferring from gas to liquid, forming solid blocks. The exothermic activity caused by temperature decreasing weakens the molecular motion and particle thermal motion of each component in the system, increasing wax precipitation rate and amount. Since the high carbon number components with lower solubility can precipitate earlier than the low carbon number components, the remaining amount of the former in the condensate system significantly decreases, leading to a decrease in its precipitation rate and proportion in the precipitated wax. The carbon number distribution curve peak of the wax shifts towards the low carbon number interval during the temperature decrease. Moreover, since the solubility of coarse-crystal wax changes more significantly during temperature decrease than that of microcrystalline wax, the precipitation activity of the former is higher in the early stage of the experiment, leading to a decrease in the proportion of the latter in the precipitated wax. However, due to the reduction of its remaining amount in the system, its precipitation rate decreases in the later stage, resulting in a relative increase in the precipitation rate and proportion of microcrystalline wax. This study can provide data reference for the formulation of wax blockage prevention and control plans of the target well section, promoting efficient oil reservoir development.