东营凹陷高青砂岩体物源方向与沉积模式研究

The Source Area and Sedimentary Pattern of Gaoqing Sand Bodies in Dongying Depression

本文基于前人研究认识与钻探实际资料等,从区域沉积特征、地震相特征、砂体分布、岩相特征和微观沉积特征等方面对高青砂岩体沉积特征进行了研究。同时,对西北部青成凸起区沉积特征的研究表明,该凸起下第三系时期为一水下高地,接受了沉积,到下第三系末,因东营运动才出露水面而成为凸起而被剥蚀,在该凸起北缓坡带残留有下第三系的沉积,凹陷南部缓坡带具有前缘端部的沉积,在此综合研究基础上,提出高青砂岩体物源区应为南部的鲁西隆起区,而非西北部的青成凸起区,其为源自南鲁西隆起而发育的由多个前缘砂朵叶体与前三角洲泥岩朵叶体叠加的复合体的新观点,并由此研究总结出了该砂岩体的沉积特征与模式;据此研究成果与勘探实践,提出了该砂岩体边角区是寻找小型岩性及岩性构造油气藏的有利相带,前三角洲泥相带部位是寻找隐蔽浊积岩岩性油气藏的有利区带;同时由于青成凸起下第三系时期为一水下高地,由此该区沙二段沉积的厚砂体———正理庄砂岩体,其物源方向也应来自南鲁西隆起区,其滚动勘探方向与潜力区应进行重新认识与评价。

Gaoqing sandbody is a well-known massive sandbody of Es 3 in southwest Dongying depression. It is more than 400 thick with an area of over 160 km 2. Gaoqing sandbody provides excellent space for oil accumulation because it overlies the main source rock of Boxing subdepression. Nevertheless, twenty years′ drilling and exploration of the sandbody has failed to find enough oil in it. The indeterminate source rock seems to be the most important factor affecting the exploration work. Based on previous studies and exploration data available, this paper has studied the depositional characteristics of Gaoqing sandbody in such aspects as regional sedimentation, seismic facies, distribution of the sandbody, lithofacies and sedimentary micro-characteristics. A study of sedimentary characte-ristics of southwestern Qingcheng convex has revealed that Qingcheng convex was a subwater convex and received deposition in Palaeogene. Due to the uplift of the convex caused by Dongying movement at the end of Palaeogene, it was denuded with some remnant sediments of Palaeogene remaining at the northern gentle slope and some progradational deposition at the southern gentle slope. It is concluded that the oil source of Gaoqing sandbody is the Luxi uplifted belt instead of the Qingcheng uplifted belt, which developed a complex made up of several progradational leafy sandbodies and litho-leafy sandbodies. The sedimentary characteristics and pattern of the sandbody are also summed up. According to the results of the study and the practical work, the authors have put forward some new viewpoints. It is believed that the corner of the sandbody is a favorable position where little litho-reservoirs and litho-structural reservoirs are accumulated, that the mudstone facies part of the front delta tends to form subtle turbidite litho-reservoirs, and that the oil source of the Zhenglizhuang sandbody, i.e., the thick sandbody of Es 2 in this region, is the southern Luxi uplifted belt, because Gaoqing convex seems to be a subwater upland in Palaeogene. The results of the study have practical reference value in search for subtle litho-reservoirs, which constitute the main goals in the exploration work of eastern China.