Controlling effect of tectonic deformation unit on vertical hydrocarbon migration and its exploration significance: a case study of Neogene oil and gas exploration in circum-Bozhong sag, Bohai Bay Basin

Vertical migration ability of faults is the key to hydrocarbon exploration in complex fault zones. This paper focuses on the problem of how to evaluate the vertical migratioa Based on the theory of pumping-driven hydrocarbon migration in combination with exploration practices of Neogene oilfield in circum-Bozhong sag, the paper proposes a concept of structural deformation unit, and the three-dimensional active fault system, instead of a single fault plane, is taken as the research object. Moreover, the quantitative calculation method of structural deformation unit is also established. The research results are as follows. (1) The intermittent stress release caused by fault activity during the accumulation period due to strong Neotectonic movement provide the power for the rapid and efficient vertical hydrocarbon migration. By comparison, the tectonic deformation unit can more objectively represent the overall activity intensity of fault zone, and further scientifically characterize the vertical hydrocarbon migration ability. (2) Structural deformation unit has two key parameters, i.e., released and involved volume, and both have a positive correlation with the vertical hydrocarbon migration efficiency. The larger the released and involved volume, the stronger the vertical hydrocarbon migration efficiency. (3) Structural deformation unit controls the vertical hydrocarbon migration in the sag, further controlling the distribution of hydrocarbon enrichment regions, zones and blocks from different aspects. The volume heterogeneity of structural deformation unit results in the formation of multiple pumping-driven hydrocarbon accumulation units, which control the stress release zone and hydrocarbon accumulation zone. The larger the structural deformation unit in a pumping element, the higher the hydrocarbon enrichment in shallow strata. In the same pumping element, the distribution of the dominant hydrocarbon enrichment zones is controlled by the tectonic deformation center. The predominant hydrocarbon charging positions are controlled by the regional strong tectonic deformation, thus forming the fault blocks of hydrocarbon enrichment. The concept of structural deformation unit provides a theoretical basis and a new idea for the quantitative evaluation of vertical hydrocarbon migration under the pumping mechanism, which is helpful to efficiently guide the discovery and evaluation of a batch of Neogene oilfields. It is of great guiding significance in re-understanding the hydrocarbon exploration and re-tapping the potential in mature exploration area, and has a wide application prospect in the exploitation of complex fault zones in subsag. © 2022 Science Press. All rights reserved.