Main controlling factors of phase evolution and charging pattern of hydrocarbons in northern Dongpu Sag

Abstract Base on statistics of gas oil ratios in reservoirs, thermal-pressure simulation experiments, and analysis of oil/gas accmulation conditions, the distribution and controlling factors of hydrocarbon phases in the northern Dongpu Sag were analyzed. From shallow to deep formations in the study area, liquid hydrocarbon, gaseous hydrocarbon containing gas condensate, and gaseous hydrocarbon were found in turn. The vertical distribution and dipartite degree of hydrocarbon phase varied among different regions, and the charging characteristics during different periods were distinctive. The evolution of hydrocarbon phase was controlled by the type of organic matter in the source rock, the thermal evolution degree of the source rock, and temperature-pressure environment of hydrocarbon migration and accumulation. In the deep formations, gases generated mainly form crude oil cracking. The majority of middle and shallow gas were evaporated from oils. There were three types of oil and gas source, including “single sag and single source”, “single sag and multiple sources”, and “multiple sags and multiple sources”, and the corresponding phase evolution patterns were defined as “early oil phase and late gas phase”, “early mixed phase and late oil phase”, and “horizontal oil phase in multiple stages”, “verticaloil phase in multiple stages”. These contributed to various oil and gas charging patterns in different sags.