New fields, new types and resource potentials of oil-gas exploration in Huanghua depression of Bohai Bay Basin

With years of intensive exploration and development, the problems of resource exhaustion and deterioration are encountered in old exploration areas, typically represented by Huanghua depression of Bohai Bay Basin, where Dagang oilfield is located. The ratio of proven resources in Huanghua depression has exceeded 50%. Among the newly proven reserves in recent years, deep and low-permeability reserves account for over 90%. As a result, it is urgent to maintain the stable production and sustainable development of crude oil in the oilfield. In recent years. China has successively made breakthroughs in exploring new types of oil and gas such as deep tight oil-gas, shale oil-gas, and coal rock gas. indicating the exploration direction for old exploration areas. Through in-depth and comprehensive analysis, it is concluded that there is still great exploration potential in 4 exploration areas of Huanghua depression, l. e. Paleogene deep depression, inner buried-hill, shale oil. and coal rock gas. Based on the re-understanding of sedimentary system and source rocks distribution characteristics, it is proposed that large sand bodies with well-matched source-reservoir assemblages are developed in deep depression, and strong oil-gas charging can lead to large- scale hydrocarbon accumulation. Moreover, the paper constructs a new model of layered petroleum accumulation in inner buried- hill. and it is pointed out that besides weathering crust, the dolomite reservoirs developed in inner buried-hill represent another new exploration field. By deepening the understanding of shale oil enrichment regularities, it has been clarified that the sweet spot layers of laminar shale and mixed shale have great potential for shale oil exploration. Boasting of wide distribution area, large thickness, moderate burial depth, and good gas production potential of the Carboniferous-Permian coal seams in Huanghua depression, as well as the discovered natural gas reservoirs from coal-measure source rocks, deep coal rock gas is a new important area for further natural gas exploration. The oil resources in four fields in Huanghua depression are estimated to be 5. 6 × 108 t, and the natural gas resources amount to 1397 × 108 m3. The breakthroughs in petroleum exploration can lay the resource foundation for the sustainable development of old exploration areas. © 2023 Science Press. All rights reserved.