Characteristics and distribution of reservoirs in Qingdong Sag, Jiyang Depression

Locating in the Jiyang Depression, the Qingdong Sag, with low exploration degree, is a recent exploration focus. Reservoir characteristics and distribution regularities were studied based on geological, seismic and chemical data. The results showed that, 3 types of crude oils developed in the study area, including salty low-mature, salty mature and normal-mature ones. The salty low-mature and salty mature crude oils both originated from source rocks in the 4th member of the Shahejie Formation, and the normal-mature crude oils originated from source rocks in the 3rd member of the Shahejie Formation. The process of petroleum accumulation was divided into 2 major phases: the first one at the end of Guantao and the second one from Minghuazhen to Quaternary. During the second phase, hydrocarbon charging was widespread, and it was the main phase for accumulation. 4 types of reservoirs generated in the Qingdong Sag, including structural, stratigraphic, lithologic and composite ones. Vertically, oil and gas mainly distributed in the upper section of the 4th member of the Shahejie Formation. On plane chart, oil and gas are abundant in the northeastern strike-slip fault zone, the northwestern slope belt, the central horst belt and the Qingdong-Qingnan transition belt, among which the northwestern slope belt was regarded as the key target for future exploration.