Hydrocarbon charging events and timing in Paleogene Hetaoyuan Formation, Biyang Sag, Nanxiang Basin

Abstract

Previous studies showed that the structure of Nanxiang Basin controlled the formation of oil and gas reservoirs, but the exact formation time of the reservoir and its coupling relationship with structural movement are not clear yet. Therefore, by analyzing the fluid inclusion system and combining with the projection method of burial history, this paper analyzed the times of oil and gas charging and accumulation in the Paleogene Hetaoyuan Formation of the Biyang Sag, and determined the age of oil and gas accumulation. The results showed that there were four phases of oil charging in two stages and one phase of natural gas charging in the Biyang Sag. The first stage mainly occurred during fault depression and uplift, including the first phase (36.1-23.5 Ma), the second phase (34.1-21.2 Ma) and the third phase (30.9-16.2 Ma) of oil charging, with the characteristics of multi-phase continuous charging. The second stage occurred during depression subsidence, including the fourth phase (7.9-0.2 Ma) of oil charging and the first phase (3.0-0.8 Ma) of natural gas charging. The early stage (the first phase) was the main formation time of oil and gas reservoirs in the Biyang Sag. The charging time of oil and gas was different in different structural zones in the Biyang Sag. The central deep subsided area and the southern slope were closer to the hydrocarbon-generating center, and were charged earlier, while the northern slope was charged relatively late. Therefore, it is recommended to focus on strengthening the vertical multi-layer and multi-stage three-dimensional exploration in the southern part of the Biyang Sag, strengthening the exploration of subtle lithology in the center, and focusing on the exploration of secondary or adjusted structural reservoirs in the north.

Keywords

• fluid inclusion
• hydrocarbon charging events
• accumulation ages
• hetaoyuan formation
• biyang sag
• nanxiang basin