GEOCHEMICAL ANOMALIES AND OIL AND GAS ATTRIBUTION OF ACID HYDROCARBON GASES FROM SEABED SEDIMENTS IN THE NORTHERN DEPRESSION, SOUTH YELLOW SEA BASIN

The stable carbon isotopic composition of the hydrocarbon gases and methane of the seabed sediments from the Northern Depression, South Yellow Sea Basin is studied for hydrocarbon gases anomalies, origin types, and attribution of oil and gases. The Northern Depression is considered as a geologically prospective area for oil and gas accumulation, not only in the Mesozoic-Cenozoic, but also in the Mesozoic-Paleozoic. Surface geochemical prospecting, base on the seabed seepage of hydrocarbons from subsurface accumulations, could be advantageous in such areas. In light of this, 100 seabed sediment samples were collected from the Northern Depression, the South Yellow Sea Basin. The geochemical anomaly distribution of acid methane and acid ethane from seabed sediments show a high anomaly area in the west and a low anomaly area in the northern depression, South Yellow Sea. C₁/(C₂+C₃)-δ¹³C₁ diagram of acid hydrocarbon gases from seabed sediments may indicate their thermal genetic type. C₁-C₂ diagram and C₁/(C₂+C₃)-C₂/(C₃+C₄)diagram show oil and gas attribution in the high anomaly area and dry gas attribution in the high anomaly area among low anomaly areas.