Sedimentary Evolution of Delta and Reservoir Distribution Under the Control of a Volcanic System

Abstract

Abstract The BZ34-9 oilfield is a clastic reservoir discovered in the Oligocene strata in the southern part of the Bohai Bay Basin. The volcanic system here is intermixed with a clastic reservoir that spans more than 1000 meters. In its upper part, it overlies about 2000 meters of Miocene strata. Volcanic activity has influenced the deposition and filling of the lacustrine and played a key role in controlling the distribution of clastic reservoirs. Based on 3D seismic data and lithological data from 74 wells, four types of volcanic were identified and extracted according to seismic sequences. Establish and clearly state the reciprocal relationship between volcanism and sedimentation. The study of volcanic stratigraphic framework reflects the environmental change of volcanoes from terrestrial to marine, which is consistent with the understanding of the sedimentary environment from paleontological and sedimentary facies studies. Small-scale volcanism predates the formation of the early Oligocene strata, and a regional eruption center to the south and east of the BZ34-9 oilfield provides the tectonic setting for the basin evolution. The early Oligocene strata was deposited in a shallow lake environment, thin-bed distributary channels are developed in the near-source facies belt near the central volcano, and thick-bed mouth dams are developed in the far-source facies belt. Volcanoes of this period influenced the distribution of clastic reservoirs by the effusion facies and intrusive facies near conical craters. Water depth becomes deeper when the late Oligocene strata are deposited, thick-bed continuous underwater distributary channels and an estuary dam is developed in the sedimentary area. Volcanic activity was moderate until the last major eruption. During this period, the hydrothermal vent in the far-source facies belt is the main factor affecting the distribution of clastic reservoirs. It is of great significance for the further fine description of reservoirs and regional exploration.