Sediment supply mechanism and its influence on hydrocarbon accumulation in the Paleogene of the northern Huanghekou Sag, Bohai Bay Basin, China

Abstract

Tectonic activity and sediment supply have significantly affected the rifted basin fillings and hydrocarbon accumulations. The Huanghekou Sag in the southeastern Bohai Bay Basin is a hydrocarbon rich sag and was bounded by the Bonan Uplift to the north in the Paleogene, which strongly affected sediment disribution and hydrocarbon accumulation in this region. The sediment supply mechanism of the Paleogene parent rocks in this area has not been revealed yet. Therefore, the Huanghekou Sag is a natural laboratory to reveal the relationship between the tectonic activties and hydrcoarbon accumulations in a rifted basin. In this study, the tectonic evolution characteristics of the Bonan Uplift in different geological periods are revealed during the main fault depression periods. Then, the direction of the provenance and distribution of the depositional system of the Bonan Uplift are analyzed based on the sedimentary system and mineralogy analysis. Finally, the sediment supply in the Bonan Uplift in different geological periods has been systematically studied. The results indicated that sediment supply is the dominant factor of hydrocarbon accumulation in the Paleogene in the Huanghekou Sag. During the Paleocene-Middle Eocene, extensive denudation occurred in the Bonan Uplift, sediments were mainly sourced from the Bonan Uplift in the northern margin of the Huanghekou Sag. During the Late Eocene to Early Oligocene, the Bonan Uplift had a large angle rotation and subsidence due to the strong rifting of the Bozhong Sag in the north, and the sand supply capacity was seriously reduced. Due to the different sediment supply in different geological periods, high quality reservoir and cap conditions were formed in the Paleogene in the central and northern parts of the Huanghekou Sag, which is conducive to the accumulation and preservation of oil and gas.