Significant Control of Gas Invasion to the Phase Behavior of Deep-Seated Hydrocarbon Fluids in Western Junggar Basin, NW China.

Abstract

In the western Junggar Basin, various oil and gas phases, such as black oil, volatile oil, condensate, and gas, have been discovered and reported. However, the primary factors responsible for the variations in oil and gas phases in different regions of the basin are not yet clearly understood. This study uses geochemical analyses, numerical simulations, and geological analyses to determine the extent of gas invasion in different regions, simulate the mechanism of gas invasion altering phase behavior, and shed light on its significant impact on fluid phases in hydrocarbons across diverse regions. The results show that the phase states of deep-seated fluids vary regionally, which is characterized by a gradual change from black oil to volatile oil, condensate, and gas from the northwest to the southeast. Gas invasion varies across oil reservoirs in different regions: the northwest regions show no significant gas invasion, the middle regions have a slight to moderate gas invasion, and the southeast regions exhibit the strongest gas invasion from heavy to severe. Varied degrees of gas invasion and corresponding phase transition rates, dependent on the gas dryness coefficient, are the primary causes of hydrocarbon fluid phase variations.