Abstract:

The volcanic activities in the Chengdao area in the middle of Bohai Bay Basin affect the development of reservoir, oil and gas migration and accumulation. The present studies mainly focus on the Mesozoic volcanic reservoir, however, the influence of the Neogene volcanic activities on the hydrocarbon accumulation are not fully understood. This restricts the further oil and gas exploration in the Eastern Chengdao. Based on the data from well logging, logging, and seismic studies, we investigated the volcanic rock lithology, lithofacies, and active characteristics, and further discussed the influence of the volcanic activities on the hydrocarbon accumulation processes. The volcanic rocks are mainly gray-black basalt, and the shape of volcanic cones is clear on the seismic section, with beaded or chain distribution on the plane. Based on the seismic facies and the electrical characteristics revealed by the drilling, the lithofacies of the Neogene bottom volcanic rocks can be divided into five types: volcanic channel facies, explosive facies, overflow facies, volcanic sedimentary facies, and intrusive facies. The volcanic activity began in the Early Neogene and lasted about 3-5 Ma before its ending, forming a localized angular unconformity and leading to the change of sedimentary environment from lake delta to braided river. With the volcanic activities and volcanic rock mass, the conditions of oil and gas transportation and lateral occlusion have been reshaped, and therefore a variety of oil and gas reservoir patterns have been established. We concluded that, the lithology relating to volcanic activities and volcanic rock mass occlusion type oil and gas reservoir are the main directions for the future explorations.

Key words: Bohai Bay Basin, Chengdao oilfield, Neogene, volcanic activity, hydrocarbon accumulation