Abstract: The processes of hydrocarbon generation, preservation and accumulation are influenced by geothermal fields of the sedimentary basins, thus hydrocarbon accumulation characteristics of low geothermal basins are different from high geothermal basins. In this paper, the geothermal discrepancies of sedimentary basins and the exploration practices of low geothermal basins in China were reviewed. Taking the Xijiang sag in the shallow water area of northern South China Sea as an example, the hydrocarbon accumulation characteristics of low geothermal rifted basins were discussed. Intensive tectonic activities during the rifting stage facilitated the formation of under-compensation lake basins, providing conditions for the development of high-quality source rocks. The low geothermal gradients could delay the thermal evolution process of the source rocks, thus postponing the periods of hydrocarbon generation and expulsion while extending the duration of oil window to facilitate more charge of crude oil. The deep sandstone reservoirs were more capable of anti-pressolution in low geothermal background, effectively protecting physical properties. In low geothermal rifts, the supercharging effect was not apparently sensitive to temperatures, leading to weak dynamics for hydrocarbon accumulation, in which circumstance most of hydrocarbons preferentially accumulated in near-source traps. Considering the exploration situation and hydrocarbon accumulation features of low geothermal basins, it is suggested that the petroleum exploration in such basins should focus on the hydrocarbon-rich sags, especially deep layers near the source rocks. Furthermore, efforts should be made to ascertain high-quality reservoir belts below the stably-distributed regional mudstone cap rocks. After elaborate evaluation of prospects, wells should be accurately deployed and drilled for significant exploration achievements.

Key words: northern South China Sea, Xijiang sag, low geothermal rift, hydrocarbon accumulation features