Abstract: Jizhong depression is the main crude oil production base in Bohai Bay Basin, boasting of rich and diversified oil and gas resources. After more than 50 years of exploration and development, the proved reserves of conventional oil and gas are very considerable. However, there is an increasing difficulty in hydrocarbon exploration. As a result, the unconventional oil and gas resources will become the key target for the next large-scale discovery. Through systematically summarizing the geological conditions for the formation of tight oil and gas in the faulted lacustrine basin of Jizhong depression, it has been determined that there are a number of sedimentary and subsidence centers and oil-generating sags and troughs in the depression, where the high-quality hydrocarbon source rocks together with fan sedimentary sands of the adjacent delta front, fan delta, and nearshore subaqueous fan or lacustrine facies carbonate reservoirs form a dominant configuration, thus providing favorable conditions for the efficient charging and accumulation of tight oil. According to the source-reservoir configuration, the tight oil and gas reservoirs in Jizhong depression can be divided into two types, i.e., extra-source and intra-source hydrocarbon reservoirs, generally showing the characteristics of large-area continuous distribution, complex lithology, non-homogeneity and near-source reservoirs. The study suggests that three types of tight oil and gas reservoirs are mainly developed in the Paleocene of Jizhong depression, including tight oil and gas conglomerate reservoirs in nearshore subaqueous fan of the steep belt (Type 1), and in fan delta of the slope belt (Type 2), as well as delta-front and shore-shallow lake facies tight oil and gas reservoirs at the peripheral of sags and troughs (Type 3), which have superior hydrocarbon accumulation conditions, demonstrating a large resources potential and a broad exploration prospect. Among them, Type 1 is mainly developed in single-faulted dustpan-like sags such as Langgu sag, Wuqing sag, Jinxian sag, and Shulu sag, with the distribution area of 476 km², the predicted oil resource of 0.53×10⁸t, and the estimated natural gas resource of 1 460×10⁸ m³. It is the main zone where breakthroughs have been made in hydrocarbon exploration of deep sags in the steep belt of Jizhong depression. Type 2 is mainly developed in Shuolu sag, Jinxian sag, and Baxian sag with narrow and steep slopes in Jizhong depression, with the distribution area of 700 km² and the predicted resources of 2.6×10⁸t. It demonstrates a realistic battleground for the realization of large-scale efficient discovery. Type 3 is mainly distributed in the lower member of the first Member of Shahejie Formation of Raoyang sag, with the distribution area of 1 214 km² and the predicted resources of 1.8×10⁸t, indicating a favorable direction for the strategic succession.

Key words: Bohai Bay Basin, Jizhong depression, tight oil and gas, geological condition, accumulation condition, resources potential

摘要： 冀中坳陷是渤海湾盆地主要的原油生产基地,油气资源丰富,油藏类型多样,历经近50年的勘探开发,常规油气资源的探明程度高,勘探难度逐步加大,非常规油气将成为下一步寻找规模发现的重点。通过系统梳理冀中坳陷断陷湖盆致密油气形成的地质条件,明确冀中坳陷发育多个沉积沉降中心和生油洼槽,其沉积的优质烃源岩与毗邻的三角洲前缘、扇三角洲和近岸水下扇沉积砂体或湖相碳酸盐岩储层形成优势配置,有利于致密油的有效充注和聚集。根据源-储配置关系,冀中坳陷致密油气藏分为源外致密油气藏和源内致密油气藏两种成藏模式,致密油气藏总体呈现大面积连续分布、岩性复杂、非均质性强和近源成藏的特点。研究认为,冀中坳陷古近系主要发育3类致密油气藏,即陡带近岸水下扇砾岩致密油气藏、斜坡带扇三角洲砂砾岩致密油气藏和洼槽周缘三角洲前缘—滨/浅湖致密油气藏,其成藏条件优越,资源潜力大,勘探前景广阔。陡带近岸水下扇砾岩致密油气藏主要发育在廊固凹陷、武清凹陷、晋县凹陷和束鹿凹陷等单断箕状凹陷,分布面积达476 km²,预测石油资源量为0.53×10⁸t,天然气资源量为1 460×10⁸m³,是冀中坳陷陡带深洼勘探突破的主要区带;斜坡带扇三角洲砂砾岩致密油气藏主要发育在冀中坳陷束鹿凹陷、晋县凹陷、霸县凹陷等具有窄陡斜坡的凹陷,分布面积达700 km²,预测石油资源量2.6×10⁸t,是实现规模效益发现的现实战场;洼槽周缘三角洲前缘—滨/浅湖致密油气藏主要分布在饶阳凹陷沙河街组一段下亚段,分布面积达1 214 km²,预测石油资源量为1.8×10⁸t,是战略接替的有利方向。

关键词: 渤海湾盆地, 冀中坳陷, 致密油气, 地质条件, 成藏条件, 资源潜力