Distribution characteristics and its controlling factor of lacustrine high-quality source rocks in the Bozhong sag, Bohai Bay Basin

Abstract

Distribution of Paleogene lacustrine high-quality source rocks in the Bozhong sag in Bohai Bay Basin is analyzed through data of geochemistry, geology and well logging, and its differences under the control of climate and tectonics is also well discussed. Distribution characteristics of the high-quality source rocks developed in the saline environment controlled by the climate are quite different from that developed in the rapid subsidence environment controlled by tectonics. The high-quality source rocks in Member 1 of Shahejie Formation developed in the saline environment account for 81.9% of total subsag area, and are distributed widely and extensively. The high-quality source rocks in Member 3 of Shahejie Formation and Member 3 of Dongying Formation is developed in the tectonic subsidence environment, and horizontally, the subsag subsidence rates has a positive correlation with the area proportion of the high-quality source rocks in the sag; vertically, the reduction-oxidation interface of the lake controls the enrichment of high-quality source rocks. Controlled by the saline environment and rapid subsidence environment, the high-quality source rocks in the Bozhong sag and adjacent areas have three types of development condition: the saline water, the tectonic subsidence, and joint control of the saline water and the tectonic subsidence. The humid climate and low subsidence rate are not favorable for development of high-quality source rocks.