陆相致密油形成地质条件及富集主控因素——以鄂尔多斯盆地三叠系延长组7段为例

Geological conditions for continental tight oil formation and the main controlling factors for the enrichment: A case of Chang 7 Member,Triassic Yanchang Formation,Ordos Basin,NW China

鄂尔多斯盆地三叠系延长组7段为典型陆相致密油大油区。以大量岩心分析及室内模拟实验为基础,结合盆地致密油勘探开发实际,研究长7段形成致密油大油区的地质条件和主要控制因素。研究表明,长7段致密油具有分布范围广、烃源岩条件优越、砂岩储集层致密、孔喉结构复杂、物性差、含油饱和度高、原油性质好、油藏压力系数低的特点。长7沉积期西南陡、东北缓的湖盆底形和活跃构造条件有利烃源岩及储集岩沉积与分布;广覆式分布的优质烃源岩为致密油大油区的形成提供充足油源;大规模沉积砂体为致密油大油区的形成提供储集条件;发育的构造裂缝是形成致密油的有利运移通道;盆地稳定的沉积及构造演化为致密油区提供良好保存条件。长7段致密油富集的主控因素:1有效源储配置和持续充注是致密油形成的关键因素;2密集发育的微小孔隙是致密油富集的前提;3持续强大的石油充注控制致密油富集高产。

The Chang7 Member of the Triassic Yanchang Formation in the Ordos Basin is a typical continental tight oil province. The geological conditions and the main controlling factors for the formation of tight oil province in Chang 7 Member were studied based on extensive core analysis data, laboratory simulation tests and practical work of tight oil exploration and development in the basin. The tight oil in the Chang 7 Member is characterized by wide distribution, excellent source rock conditions, tight sandstone reservoirs, complicated pore-throat structure, poor physical properties, high oil saturation, high quality oil, and low pressure coefficient. During the depositional period of Chang7 Member, the bottom shape of the basin was steep at southwest and gentle at northeast, the tectonic movements were active, favorable for the deposition of source rock and reservoir; the widespread high quality source rock can provide sufficient oil supply for the large tight oil province; the large scale sand bodies provide good reservoir condition for the large tight oil province; the abundant structural fractures in the tight reservoir act as pathways for tight oil migration; and the stable deposition and tectonic evolution of the basin provide good preservation conditions for the tight oil province. The main controlling factors of Chang7 Member tight oil enrichment are as follows： （1） good configuration of source rock and reservoir and constant charging are the key to the formation of the tight oil province; （2） abundant micro-scale pores are the premise of tight oil enrichment; （3） strong and sustained charging guarantees the enrichment and high yield of oil in the tight reservoirs.