关键词: 渤海湾盆地, 黄骅坳陷, 致密油气, 资源潜力, 成藏条件, 成藏期次

Abstract: Huanghua depression in the Bohai Bay Basin has gone through three stages of structural-lithological reservoir exploration, lithological reservoir exploration in slope zones, and lithological reservoir exploration in deep subsag zones. The cumulative proven petroleum geological reserves in Huanghua depression exceed 1.3×10⁸t, and more than 50 % of conventional petroleum reserves have been proved, indicating that the whole Huanghua depression has entered a highly mature exploration stage. By contrast, there are tight oil and gas of low exploration degree and large remaining oil and gas resources in Bohai Bay Basin, which is an important exploration field for Dagang oilfield to increase reserves and production in the future. Based on the data of drilling, geophysical survey, and experimental test in recent years, the paper systematically analyzes the favorable hydrocarbon accumulation conditions, accumulation periods, accumulation model, and resource potential of tight oil and gas in Huanghua depression. The research results show as follows. (1)Huanghua depression possesses favorable conditions for the accumulation of tight oil and gas. The fault activity and thermal subsidence that have a controlling effect on the basin and depressions have led to the formation of vast reservoir spaces in deep layers of the basin, providing a favorable tectonic setting for the input of sedimentary provenance. During the depositional periods of the Kongdian Formation, Shahejie Formation, and Dongying Formation, sand bodies were widely distributed. The four main source rock formations, i.e., Member 2 of Kongdian Formation (E₂k₂), Member 3 of Shahejie Formation (E₃s₃), Member 1 of Shahejie Formation (E₃s₁), and Member 3 of Dongying Formation (E₃d₃), are widely distributed in Huangye depression, and have high hydrocarbon generation intensity and superior hydrocarbon supply conditions, which can provide an important resource foundation for the enrichment of tight oil and gas. Strong dissolution leads to the development of dissolution pores in tight oil and gas reservoirs, thus improving the reservoir conditions. There are three types of source-reservoir assemblage patterns, i.e., lower generation and upper accumulation pattern, three-dimensional filling pattern, and lateral hydrocarbon migration and accumulation pattern, demontrating excellent conditions for configuration of source rocks and reservoirs. (2)There are two main accumulation periods of tight oil and gas in Huanghua depression, i.e., sedimentary period from Shahejie Formation to Dongying Formation and sedimentary period from Minghuazhen Formation to the present. The tight oil and gas reservoirs in Huanghua depression are mainly developed in the deep subsag zone and the lower step fault zone around the sag, with the characteristics of "source-reservoir coupling and continuous accumulation". (3)Huanghua depression is rich in tight oil and gas resources, including the tight oil resources of 2.82×10⁸t, 1.17× 10⁸t and 5.92×10⁸t in E₂k₂ of Cangdong sag, Dongying Formation and Shahejie Formation of Qikou sag, respectively, and also the tight gas resources of 2 875×10⁸m³ in Shahejie Formation of Qikou sag. Based on the comprehensive evaluation and analysis of petroleum geological conditions, remaining oil and gas volume, and exploration practice of different layers of petroleum systems in each area, it is determined that the E₂k₂ of Cangdong deep subsag zone, E₂k₂ of Changzhuang subsag, and Dongying Formation of Qikou deep subsag zone are favorable new areas for exploration of tight oil, and the E₃s₃ of Banqiao subsag and southwestern edge of Qikou sag are favorable new areas for exploration of tight gas. The new understandings of geology and resource potential resulted from the breakthrough in tight oil and gas exploration can provide technological support for the subsequent sustained and highly efficient exploration in Huanghua depression.

Key words: Bohai Bay Basin, Huanghua depression, tight oil and gas, resource potential, accumulation condition, accumulation period