GEOCHEMISTRY AND SOURCE ANALYSIS OF OIL FROM SHA3 FORMATION IN SOUTHERN BEACH SEA AREA, DAGANG OILFIELD

Southern beach sea area in Dagang Oilfield is adjacent to Qikou and Qinan hydrocarbon generation sags, and has the advantage of bidirectional source. Sha3 Formation is the major pay bed in the studied area, but the oil-source correlation in this formation is still disputed. In order to clarify the oil source, some indexes and geochemical characteristics are analyzed and correlated, such as group composition, carbon isotopes, i-paraffins, steroids and terpenoids, and oil is classified. The result shows that the oil in Sha3 Formation of southern beach sea area can be classified into 3 types. Type Ⅰ is mainly derived from the source rock in Sha3 Formation, type Ⅱ mainly from the source rock in Lower Sha1 Formation, and type Ⅲ is the mixed source of Lower Sha1 and Sha3 since the geochemical characteristics are between the first two types. The distribution characteristics of these three types of oil are regionally different.