湖相碳酸盐岩油气藏特征及成藏分析——以柴达木盆地南翼山油气藏为例

Pool Features and Hydrocarbon Accumulation Analysis of Lacustrine Carbonate Rock:Take Nanyishan Reservior in Qaidam Basin as an Example

通过对柴达木盆地南翼山碳酸盐岩油气藏下干柴沟组(E3)至上油砂山组(N22)储层和油藏特征进行系统研究,认为与湖相碎屑岩油气藏相比,南翼山湖相碳酸盐岩油气藏在生、储、盖、生储盖组合、圈闭类型和油气藏类型及其组合关系等方面都有其特殊性,主要体现在:①南翼山构造处于生烃凹陷,存在多套烃源岩,油气就近捕获;油源来自南翼山的西南小梁山凹陷,深层E23原油来自E23烃源岩,浅层N2原油来自N1烃源岩。②南翼山共存在4套含油气层系(E3、N1、N12、N22),可分为2类:一类是中浅层(N1—N22)发育在构造背景上的以泥晶灰(云)岩、藻灰(云)岩和颗粒灰(云)岩为储层,以粒间孔和溶蚀孔为储集空间的层状岩性油气藏;另一类是E23上部,以泥灰(云)岩为储层,以孔隙—裂缝为储集空间的凝析气藏。③南翼山油气藏碳酸盐岩储层与泥岩垂向上构成频繁互层的生储盖组合。④南翼山N22油气藏油层薄,渗透率低,驱动类型以弹性驱动和溶解气驱为主,油藏类型是受背斜构造控制的岩性层状油藏;中深层凝析气藏气层纵向集中,平面受构造和断层控制;裂隙性储集空间,产能不一。⑤南翼山油气田成藏主控因素主要包括南翼山构造处于生烃凹陷、油气就近捕获,断裂和断裂系统是良好的疏导体系,湖相碳酸盐岩储层是油气聚集成藏的关键。⑥南翼山构造在上新世之前背斜构造发育缓慢,发育高峰期在上新世早中期,并最终定型;上新世早中期下干柴沟期进入生烃高峰,形成自生自储的油气藏;上新世晚期—第四纪上干柴沟期进入生油高峰,油气沿构造两翼断层运移至N1、N12和N22成藏。

Based on the reservoir and hydrocarbon pool characteristics from Lower Ganchaigou Formation to the Upper Youshashan Formation of carbonate hydrocarbon pool in Nanyishan, comparing with lacustrine elasolite hy- drocarbon pool, we found there are differences in source, reservoir, cap, source-reservoir-cap assemblage, trap type, type of oil and gas pools, and relation of all the above in Nanyishan lacustrine carbonate oil and gas pools as fol- lows： （1）Nanshishan structure located in the hydrocarbon-generation kitchen, with numbers of source rocks, and hydrocarbon can be captured from the nearby area. The oil source came from Xiaoliangshan Sag, on the southwest of Nanyihshan. Crude oil in E23 in the deep was from the source rock in E23 ,while N2 was from N1. （2）Four hydro- carbon-bearing series in Nanyishan can be grouped into two types. One is a layered lithologic reservoir controlled by the structure in middle-shallow layer. Lithology of the reservoir is micrite limestone or dolomite, algal limestone or dolomite and grain limestone or dolomite. Intergranular pores and solution pores are storage space. The other was a condensate gas pool in the upper E32, taking marlstone or argillaceous dolomite as reservoir and pore-fissure as storage space. （3）The Nanyishan carbonate reservoir and mudstone formed source-reservoir-cap assemblage fre- quently interbedded in vertical. （4）Nanyishan pool in N22 had characteristics such as thin reservoir and low permea- bility. It had elastic drive and solution gas drive as main drive type. Layered lithologic reservoir is controlled by anti- cline structure. While gas layer of the middle deep condensate gas pool was concentrated in vertical and dominated by the structure and fracture in plane. The productivity capacity was quite different due to fissure storage space. （5） There are three main controlling factors on the formation of Nanyishan pool： Firstly, Nanshishan Structure located in the hydrocarbon-generation kitchen. Hydrocarbon can be captured in the nearby area. Secondly, the fracture and fracture system contributed to the translocating system. Finally, the lacustrine carbonate reservoir played aa key role in the formation of oil and gas pools. （6）Nanyishan structure developed slowly before Pliocene, and the develop- ment peak was in Early-Middle Pliocene,but then it stopped . The Lower Ganchaigou Formaion had hydrocarbon generation peak in Early-Middle Pliocene and it formed an authigenic reservoir. The Upper Ganchaigou Formation came into oil generation peak from late Pliocene to Quaternary, and along the northern and southern wing in the structure oil and gas migrated into N1、N12, N22 and the reservoirs formed finally.