渤海海域深层天然气勘探的突破与启示

传统的观点认为：渤海湾盆地属于中国东部典型的油型盆地,难以形成大型天然气田,而近期渤中19-6深层天然气田的发现则展示了渤中凹陷深层巨大的天然气勘探潜力。为了给渤海湾盆地及其他地区的深层天然气勘探提供指导和借鉴,对该区深层天然气的成藏模式、主控因素及富集规律等进行了研究。研究结果表明：①渤中凹陷厚层腐殖-腐泥型烃源岩在深埋条件下具有高成熟阶段富气的特点,具备形成大气田的物质条件;②岩石类型-应力改造-流体溶蚀联合控制了深部古近系碎屑岩及太古界变质岩超大规模储层的形成,为大型天然气田的形成提供了储层条件;③渤中凹陷巨厚超压泥岩形成的区域性盖层,为大规模天然气的汇聚成藏创造了有利的封盖及保存条件;④确立了渤中凹陷深层先油后气大型天然气田气侵式成藏模式,以巨大供油窗、快速成藏、内幕运移为其特点。结论认为,渤中凹陷深层天然气勘探之所以能够取得突破,主要得益于长期坚持“在油型盆地找大气田”的战略部署,得益于打开思路、精细研究、模式创新和技术进步。

The breakthrough of the deep-buried gas exploration in the Bohai Sea area and its enlightenment

It is generally thought that the Bohai Bay Basin belongs to a typical oil-type basin in the eastern China, where, for lack of gas reserves, giant gas fields will be difficult to be formed, however, the latest discovery of the Bozhong 19-6 deep gas field shows a great potential of natural gas resources in the deep strata of the Bozhong Sag. In order to give some guidance for deep-strata gas exploration in the Bohai Bay Basin and other areas, we discussed the accumulation modes, controlling factors and enrichment laws in this study area. The following findings were achieved. (1) Thick humic–sapropelic source rocks buried deep in the Tazhong Sag have the characteristics of gas enrichment in high maturation stage under deep burial and the material conditions of forming large-scale gas fields. (2) The combined main forces of rock types, stress transformation and fluid dissolution controlled the giant-scale formation of the deep-buried clastic rocks and metamorphic rocks, which provides favorable reservoir conditions for the formation of large-scale gas fields. (3) The regional caprocks of thick-deposited and overpressured mudstones in the Tazhong Sag provide sealing and preservation conditions for large-scale natural gas pools. (4) A large-scale gas field intrusive accumulation model was proposed to explain that gas accumulated later than oil in the Bozhong Sag, characterized by abundant gas supply, late-stage fast accumulation and insider migration. In conclusion, such a breakthrough made in gas exploration in this study area is attributed to the long-term strategic deployment of "Discovering Large-scale Gas Fields in Oil-type Basins" and the opening up of thoughts, fine research, model innovation and technological progress.