柴达木盆地西北缘新近系上油砂山组烃类流体特征与铀成矿的关系

通过对柴达木盆地西北缘新近系上油砂山组18个样品的酸解烃分析,探讨了酸解烃中烃类气体组成特征、成因及来源,并结合该区铀矿地质特征初步分析了烃类流体与砂岩型铀成矿关系。酸解烃的分析结果表明,新近系上油砂山组砂岩层中烃类气体为有机成因的油型气和煤型气的混合气。烃类气主要处于成熟—高成熟阶段,是原油裂解气与原油伴生气的混合气,主要来源于路乐河组和下干柴沟组湖相腐泥型烃源岩。这些原油裂解气和原油伴生气的混合气主要沿断裂、微裂缝等通道向上运移到上油砂山组砂岩中,上油砂山组灰绿色砂岩即是烃类气体对红色砂岩还原的产物。研究区砂岩型铀矿成矿作用为原生红色—后生还原灰绿色的氧化还原作用过程,找矿标志为灰绿色含砾砂岩、砂砾岩,灰绿色砂岩层的古迎水面为该地区的找矿方向。

柴达木盆地宗马海湖地区中新统上油砂山组轮藻植物群

我国西北地区的柴达木盆地沉积了巨厚而连续的新生代陆相地层,其北缘宗马海湖地区中新统上油砂山组非常发育,在一道梁剖面出露良好。本文首次报道并详细描述了该剖面上油砂山组的岩性特征,主要为褐红色、灰绿色和灰色砂岩、粉砂岩夹泥岩,发育滨、浅湖沉积相。共发现轮藻化石2属2种:Nitellopsis(Tectochara)merianii和Lychnothamnus barbatus var.antiquus.这两个种广泛分布于欧亚大陆,前者的延限从晚始新世至更新世;后者在我国可能为首次报道,之前仅见于欧洲和土耳其某些地区的中新统地层。根据轮藻化石的时代延限,上油砂山组的沉积时代为中新世,与已有古地磁研究结果一致。对上述两种轮藻化石的现生相关类群的生活环境分析表明,N.(T.)merianii和L.barbatus var.antiquus可能生活于大型冷水、淡水湖泊,这与沉积相分析结果一致。

Reservoir formation conditions and key exploration & development technoloiges in the Yingdong Oilfield in western Qaidam Basin

Located in east part of Yingxiongling structural belt in the Qaidam Basin,the Yingdong oilfield has a extremely complicated ground condition.Due to no significant discovery,this oilfield was considered to have no favorable geologic conditions for formation of oil or gas reservoir.In the past few years,with continuous improvement in the mountain 3D seismic surveys and logging data interpretation,some breakthroughs were obtained in 2010,and the Yingdong oilfield,the largest-scale reserves of a single reservoir with highest organic matter abundance,most favorable physical property and optimal development efficiencies in the Qaidam Basin,had been discovered,the production capacity was up to 0.55×10^(6) t.Through detailed analyses of the Yingdong oilfield,some studies,such as hydrocarbon accumulation conditions and technical challenges,are carried out,and following conclusions can be achieved.The Yingxiongling area is located in Mangya hydrocarbon-generation sag in the west part of the Qaidam Basin,its oil sources are rich;the Neogene Xiayoushashan Formation and Shangyoushashan Formation are dominated by wide and gentle delta frontdshore-shallow lacustrine sediments with interbeds of sandstone and mudstone,the sandbodies are widely distributed with favorable physical condition,and the mudstone is the key caprock,combined with high-quality Paleogene hydrocarbon source rocks,a complete source-reservoir-cap assemblage can be formed.Large-scale detachment faults of the Yingdong area connect high-quality Paleogene hydrocarbon source rocks with middle-shallow buried structural traps,thus,reservoirs formed in the early stage are modified,and at the same time,hydrocarbons formed in the later stage continue to migrate and accumulate;in this way,the deep and shallow faults form a relay-style hydrocarbon transport system,and hydrocarbons are accumulated in the shallow structural traps in the later stage;in this area,the middle-shallow faults have good lateral plugging performance which is favorable for preservation of oil and gas.For complex landforms and reservoir features in the Yingdong area,the integral 3D seismic acquisition,processing and interpretation technology is developed for complex mountain areas to provide a reliable foundation for hydrocarbon exploration.For some problems in the Yingdong oilfield like long oil/gas-bearing intervals,great diffi-culty in identification of fluids,the development mode of multiple oil/gas/water systems in the long intervals is established,and the geologic modeling technology with constraint of multiple conditions on complex fault blocks is also developed.Thus,hydrocarbon accumulation mechanism in the Yingdong oilfield is clear,and some complex key technology of engineering are well solved,providing necessary geologic theories and technical supports for high-efficiency development and rapid production construction in the Yingdong oilfield.

柴达木盆地西缘砂岩型铀矿元素地球化学特征及其地质意义

为揭示柴达木盆地西缘英东地区上油砂山组含铀砂岩源岩风化程度、物源性质及构造背景,以区内最新发现的工业铀矿孔ZKY01中上油砂山组含矿砂岩为研究对象,通过岩心和显微观察、扫描电镜和地球化学分析,探讨了区内含矿砂岩的岩石学特征、地球化学特征、风化作用特征、物源特征及沉积构造背景,并结合地质特征,初步分析了油气与砂岩型铀成矿的关系。结果显示,上油砂山组含矿砂岩以长石岩屑砂岩为主,铀矿物主要有钒钙铀矿、钒钾铀矿、沥青铀矿和铀石;分异指数CIA和风化指数ICV表明含矿砂岩成分变化程度低,为构造带首次沉积,没有经历沉积再循环过程。物源以中酸性岩浆岩为主,源区具有主动大陆边缘和大陆边缘弧的构造背景;δEu、δCe与U呈微弱正相关,U富集过程由氧化向还原环境转变。结合铀成矿地质条件认为,上油砂山组含矿目的层中铀矿化与油气关系密切,油气的上侵提升了砂体的还原能力,有利于砂岩型铀矿的形成。