渤海海域陡坡带地层划分技术与应用

MESOZOIC STRATIGRAPHY OF THE BOHAI BAY BASIN

随着油气勘探的不断深入,在渤海海域陡坡带古近系相继发现了一些大中型油气藏,但陡坡带的地层划分十分困难,其一是新老化石分子共存,一般认为出现新的化石组合意味着钻遇新的地层,但这种地层划分方法有时与周边地层矛盾,在地震上无法跟踪对比;二是边界断层下降盘巨砾岩年代归属问题,由于岩石碎屑粒径远远大于钻头直径,获取的岩屑见不到原始颗粒面,很难确定钻入的是否风化壳、基底本体。陡坡带地层分析技术是一门新兴的地层分析技术,包括3项技术即钻时岩屑复合技术、电测井岩屑复合技术和化石组合和保存状态复合技术,根据钻井取样中发现的化石保存状态及其组合关系、岩性和配置关系,结合钻时、岩屑录井及其测井响应,识别再沉积、巨砾岩、风化壳和底砾岩。解决地层归属问题有助于陡坡带构造演化和成藏研究,对现场施工也有重要意义,同时,也为凸起区地层缺失原因研究提供了新的思路和方法。

The Bohai Bay Basin is covered with seawater, and the Mesozoic stratigraphy of the Bohai Bay Basin is poorly understood. Mesozoic strata in the Bohai Bay Basin were previously divided at the system and series levels. Based on drill core, well log, and seismic reflection data, we divide Mesozoic strata in the Bohai Bay Basin into 10 formations, seven of which have been penetrated by drill cores, including the Jurassic Haifanggou and Lanqi formations and the Cretaceous Yixian, Jiufotang, Shahai, Fuxin, and Sunjiawan formations. Mesozoic strata of Bohai Bay Basin can be correlated with those in western Liaoning Province. The thickness and distribution range of each formation is controlled by fault development and is highly variable.