鄂尔多斯盆地志丹地区延长组长7致密油成藏条件与成藏特征

采用地质与地球化学相结合的研究方法,通过致密油分布、物理性质、油源地球化学特征、储层特征及非均质性、圈闭条件及油水分布特征综合分析长7致密油成藏条件、主控因素与成藏特征。结果表明:长7致密油藏具备形成准连续型油气聚集的成藏地质条件和特征;长7油层组中发育优质烃源岩,主要以长7³中的张家滩页岩为最优,烃源岩分布范围控制了致密油成藏外边界,烃源岩厚度大于20 m地区为最有利成藏区;长7致密油成藏具有良好的生、储、盖组合配置,重力流砂体主要呈透镜状或条带状分布于泥岩或油源岩中,具有优先捕集油气的优势;长7致密油成藏对圈闭要求相对较低,其遮挡条件主要为岩性、物性及成岩边界,动力圈闭也是重要的圈闭类型。长7致密油富集与局部构造背景没有直接的关系,而主要取决于储集层展布及物性;高强度生、排烃及强充注造成长7储层原始含油饱和度较高;受原始物质组成及成岩强度的影响,长7储层非均质性很强,致使油、气、水在致密储层中分异差,油、水分布复杂。

Accumulation conditions and characteristics of the Chang 7 tight oil reservoir of the the Yanchang Formation in Zhidan area,Ordos Basin

Through integration of geological and geochemical data,this paper comprehensively analyzed the conditions,main controlling factors and characteristics of oil accumulation in the Chang 7 tight oil reservoir from such aspects as the tight oil distribution,physical properties,geochemical features of the oil source,reservoir characteristics and heterogeneity,trap conditions,and oil and water distribution.The following results were obtained.The Chang 7 tight oil reservoirs own the geological conditions and characteristics for the formation of quasi-continuous oil and gas accumulation.The Chang 7 reservoir interval contains high-quality source rocks,of which the Zhangjiatan shale in the Chang 7³ layer is the best one.The outer boundary of the tight oil reservoirs is controlled by the distribution of the source rocks.The favorable area of hydrocarbon accumulation occur in where the thickness of hydrocarbon source rocks is over 20 m.The Chang 7 tight oil accumulation has favorable source-reservoir-seal assemblages and the gravity flow sandbodies occur in the mudstone or source rocks mainly in lenticular or stripped shapes,thus are advantageous in trapping oil and gas.The importance of trapping conditions is relatively low for the accumulation of oil in the Chang 7 tight reservoir,as the main seals are lithological,physical property and diagenesis boundaries.Dynamic trap is also an important trap type.Oil enrichment in the Chang 7 tight reservoir has no direct relationship with the local tectonic background,instead is mainly controlled by reservoir distribution and their physical properties.The high intensity of hydrocarbon generation,expulsion and charging results in the relatively high original oil saturation in the Chang 7 reservoir.Due to the influences of the origin material composition and diagenetic intensity,the Chang 7 reservoir is of strong heterogeneity,resulting in the poor differentiation of oil,gas and water,and a complicated oil-water contact in the tight reservoir.