渤海湾盆地大型变质岩潜山油田勘探发现及地质意义

Discovery of large-scale metamorphic buried-hill oilfield in Bohai Bay Basin and its geological significance

渤海湾盆地渤南低凸起西段太古宇潜山带具有良好的油气成藏条件,渤中26-6油田是整装的太古宇油田,原油探明储量超亿吨。利用大量岩心、岩石薄片、测井和地球化学等资料对渤中26-6油田进行系统研究后认为:太古宇潜山储层在垂向上可划分为风化砂砾岩带、风化裂缝带和基岩带,其中,风化裂缝带是最主要的储层发育带;在印支期、燕山期、喜马拉雅期3期构造运动下形成的裂缝是太古宇潜山储层发育的基础,印支期的挤压碰撞与燕山期的走滑逆冲是裂缝形成的主要动力,喜马拉雅期近SN向的伸展作用保持了先期裂缝的有效性;在裂缝沟通下,大气淡水溶蚀形成了面积广泛的潜山优质储层,距不整合面约420 m以浅的范围是优质储层发育段;潜山上覆盖的“弱超压、强稳定”东营组泥岩为大型油藏的保存提供了良好的封盖条件;渤中26-6油田太古宇潜山与其南侧的黄河口凹陷烃源岩直接接触,与北侧的渤中凹陷烃源岩以不整合面相连,形成了多元立体油气运移充注模式。上述认识指导了渤中26-6油田太古宇高丰度油藏的高效勘探,进一步完善了渤海湾盆地深层太古宇潜山的成储、成藏模式,对于渤中凹陷西南环太古宇潜山带的油气勘探具有重要的指导意义。

Archean buried-hill zone in the western section of Bonan low salient of Bohai Bay Basin has good conditions for hydrocarbon accumulation.Bozhong26-6 oilfield is an Archaean integrated oilfield with proven reserves of crude oil exceeding 100 million tons.Based on a large number of core,thin section,well logging and geochemical data,a systematical study was performed on Bozhong26-6 oilfield.The analysis suggests that the Archean buried-hill reservoirs can be vertically divided into weathered conglomerate zone,weathered fracture zone and bedrock zone,among which the weathered fracture zone is the key reservoir development zone.The superimposed fractures formed by the Indosinian,Yanshanian and Himalayan movements provided the foundation for the development of Archaean buried-hill reservoirs.The Indosinian compression and collision and the Yanshanian strike-slip thrust were the main driving forces for the formation of fractures,and the south-north extension of the Himalayan epoch maintained the validity of earlier fractures.Under the communication of fractures,a wide area of high-quality buried-hill reservoirs is formed by the dissolution of atmospheric fresh water,and the high-quality reservoirs are developed in the zone within 420 m away from the unconformity.The mudstone of Dongying Formation with weak overpressure and strong stability overlying buried hill provides good sealing conditions for the preservation of large-scale oil reservoirs.The Archean buried hills are in direct contact with the source rocks of Huanghekou sag in the south,and are connected with the source rocks of Bozhong sag in the north by the unconformity,thus forming a multi-dimensional oil-gas migration and charging mode.In conclusion,the above findings provide a guidance for the efficient exploration of Archean high-abundance oil reservoirs in Bozhong26-6 oilfield,further improve the hydrocarbon accumulation and reservoir mode of deep Archean buried hills in Bohai Bay Basin,and are of important guiding significance for the oil and gas exploration of the Archean buried hill zone around the southwest Bozhong sag.