The Spatial Variation and Control Factors of Hydrocarbon Properties in J Block of the South Sumatra Basin

ABSTRACT The analysis and prediction of oil and gas properties and phase states are key steps in increasing production, and an important prerequisite for clarifying the formation and distribution mechanisms of oil and gas. Although the oil and gas sources in J Block of the South Sumatra Basin are consistent, the properties of the oil and gas vary greatly in space, and the difference aggregation law on the plane is not obvious. It is urgent to have a deeper understanding of the spatial properties and distribution laws of oil and gas. Based on PVT (pressure, volume, temperature) data of oil and gas and geochemical data of source rocks in J Block, this paper uses source rock and hydrocarbon data analysis, hydrocarbon generation kinetics and thermal simulation, and PVT phase simulation to analyse the influence and control of source rock organic phase and maturity, and phase separation on the spatial distribution of oil and gas properties. The results show that J Block exhibits a spatial distribution of ‘gas above, oil below’. The source rocks are mainly facies D/E and F in LTAF. Most of the oil and gas are saturated fluids, and the saturation pressure is the key factor controlling hydrocarbon properties. The hydrocarbon accumulation process in J Block is as follows: The facies D/E and F source rocks in LTAF exhibit an ‘early oil, late gas’ hydrocarbon generation and expulsion process. The black oil expelled from the middle Miocene to late Miocene formed an unsaturated normal oil reservoir in the deep layers, while the gas condensate expelled from the late Miocene and early Pliocene to the present underwent ‘phase separation’ to form two phases of gas condensate and light oil as the formation pressure gradually decreases to saturation pressure in the process of upward migration.