三塘湖盆地牛圈湖油田地质特征与成藏过程

The Geologic Feature and Hydrocarbon Accumulation of Niujuanhu Oilfield in Santanghu Basin

以油气藏基本特征为基础,通过沉积与储盖组合特征和成藏期次分析,对牛圈湖油田的油气成藏过程进行了动态恢复。牛圈湖油田沉积与储盖组合良好。原油主要来自于上二叠统芦草沟组湖相烃源岩,以低成熟油为主。下侏罗统西山窑组主要为扇三角洲相、河流相和湖沼相沉积,岩性为砂岩、砂砾岩等,砂岩储集空间为粒间原生孔隙和粒间溶孔,为低孔低渗的孔隙型储集层。芦草沟组沉积相主要为滨浅湖-半深湖相、火山喷发相和河流相沉积。储集层储集空间包括孔、缝、洞,但以孔、缝为主,为裂缝-孔隙型储集层,其原油属于自生自储。油气成藏既有阶段性,也有较好的持续性。芦草沟组油藏的油气聚集开始于三叠纪末,侏罗纪末-白垩纪是成藏的主要时期。侏罗系油藏主要形成于白垩纪晚期。喜马拉雅运动期是不同层位油藏的重要保存期。

The basic characteristics of oil-gas reservoir are presented, the deposition, reservoir-cap rock assemblage and hydrocarbon accumulation stages are analyzed and the process of hydrocarbon accumulation is dynamically recovered in Niujuanhu oilfield. It is shown that it is in good assemblage and its crude oil originates from lacustrine source rocks of Lucaogou formation of Upper Permian, dominated by low-mature oil. The Xishanyao formation of Lower Jurassic is characterized by fan delta, fluvial and lacustrine deposits with sandstone and glutenite, etc. and primary intergranular pore and intergranular dissolved pore, belonging to porous-type reservoir of low porosity and low permeability. Lucaogou formation is characterized by coastal lake, hemi-deep lake, volcanic eruption and fluvial deposits with pore, fissure and cavity, being fracture-pore-type reservoir. Its crude oil originates from both source and reservoir in itself, and its hydrocarbon accumulation occurs in several stages and durative and starts from Late Triassic, but the main stages are Late-Jurassic to Cretaceous. Jurassic reservoir is principally formed at Late Cretaceous. Himalayan movement period is significant to the preservation of different horizons of reservoirs in this basin.