TYPES OF UNCONFORMITY AND PREDICTION OF HYDROCARBON RESERVOIRS IN YANTAI DEPRESSION, SOUTH YELLOW SEA BASIN

A large number of research data show that the formation of many hydrocarbon basins worldwide are related to the unconformity, such as the Anadarko Basin in United States, Maracaibo Basinin Venezuela, the western Canada Athabasca oil and gas fields, the Qijiahe super-unconformity oil and gas reservoirs in the Liaohe Basin, China, the stratigraphic truncation-unconformity reservoirs in the Jungar Basin, China.

The South Yellow Sea basin is a superimposed basin developed on the base of the Sinian metamorphic rocks, composed of thick Neoproterozoic Sinian, Paleozoic and Cenozoic deposition. The Neoproterozoic Sinian to the Lower Triassic is dominated by marine deposition, whileno deposition is preserved during the Middle Triassic and Upper Triassic period. During the Jurassic to the Neogene period, the terrestrial deposition is predominant, while the lower and upper part of the Quaternary is dominated by terrestrial and marine deposition respectively.

This study focuses on the Jurassic-Paleogene deposition in the Yantai Depression of the northern Yellow Sea basin, the base of the fault period is also considered. Due to the influence of Indosinian movement, Yanshan movement and Himalayan movement, many tectonic uplift and subsidence occurred in the South Yellow Sea basin, forming a multi-layer unconformity, including the unconformity at the top of basement, Jurassic, Cretaceous, Paleogene, Paleogene strata. According to the contact relation, unconformity angle and fault base characteristics of the strata shown on the seismic profile, five kinds of unconformity are divided, namely parallel unconformity, truncation unconformity, truncation-overlap unconformity, fold unconformity, bedrock erosion unconformity.

According to the “Source Control Theory”, the unconformity associated with the semi-deep to deep lacustrine facies in the northern depression of the Yantai Depression in the northern part of the South Yellow Sea could be favorable for the hydrocarbon reservoirs. The types of hydrocarbon reservoirs are stratigraphic overlap reservoirs, stratigraphic truncation reservoirs, truncation-overlap reservoirs, compression fold unconformity reservoirs, erosion buried hill reservoirs. Among these, the overlap – truncation reservoirs and erosion buried hill reservoirs are predominant.