【作者】 刘海涛；

【导师】 马立祥；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2004， 硕士

【摘要】 柴达木盆地的油气勘探自 1954 年以来已经有 50 年的历史,已形成“北部侏罗系找油、西部第三系找油和东部第四系找气”的勘探格局,而柴西地区探明的石油地质储量占整个盆地的 90%以上。尽管近年来在西部地区油砂山、七个泉、狮子沟、花土沟等油田做了大量的石油地质综合研究,但是盆地西部地区毗邻阿尔金山、昆仑山和祁连山,构造活动强烈,储集体分布复杂多样,对成藏规律的认识尚不十分清楚,因此利用盆地分析、含油气系统等学科理论在该地区开展较详细的主要成藏期沉积、古构造的配位与远景区带的预测研究,对降低油气勘探风险,提高该区的勘探效率和获得巨大的经济效益,具有重要意义,从而更加科学地为选择有利的油气勘探目标提供依据。 本次研究目的层新生代地层自下而上为古新统路乐河组、早始新统下干柴沟组下段、中始新统下干柴沟组上段、晚始新统-渐新统上干柴沟组、早中新统下油砂山组、晚中新统上油砂山组、上新统狮子沟组和更新统七个泉组,本文分析了古水流及沉积古地貌进而确定柴西地区不同时期沉积相展布,其主要的沉积体系有(浅水)扇三角洲、冲积扇、洪积扇、滨浅湖、半深湖、冲积平原及滨岸沉积。 面对今柴达木盆地复杂的构造形变,仅从构造解译的角度来反演盆地的演化历史是不够的,需从沉积盆地不同阶段的古构造和沉积体充填的几何形态及岩相带的分布,去客观认识柴达木盆地的演化过程和认识盆地演化的动力学过程,这是一条可行的途径。柴西地区中、新生代以来沉积响应特征表明该地区经历了燕山期-喜山期的多次具有不同动力学性质的地壳变动:中生代的走滑伸展裂陷、新生代古新世-中始新世的伸展裂-坳、晚始新世-更新世的伸展走滑坳陷和更新世末-今的挤压挠曲走滑等四个盆地构造动力学阶段。因此按构造动力学分类,柴达木盆地自中生代以来,经历了上述四种类型盆地的演化,形成了现今复杂变形盆地的构造格局。 通过分析柴西地区早中始新世上干柴沟组沉积前、晚始新世-渐新世下油砂山组沉积前、中新世上油砂山组沉积前和更新世后 Q3+4 沉积前等四个阶段的区域古构造特征可知,该地区在以狮子沟-红三旱三号为轴线的广大地区属于沉降区,这与自古近纪古新世以来,继承性的沉降中心发育区相吻合,同时也表明柴西地区在更新世末以后盆地才发生北北东方向大规模强烈的挤压挠曲褶皱、逆冲、断裂变形,而在更新世早期及以前,盆地演化的主要动<WP=7>力学机制是以伸展裂坳-坳陷为主。 从柴西地区主要成藏期次分析来看,其具有多期成藏的特点。首先,由于在不同部位构造沉降史和沉积条件的差异,即使是同一套烃源岩,在不同构造单元其热降解程度与时期也是不一致的,总体上东昆仑山前缘以及阿拉尔地区相对成熟较晚,而柴西地区的东部尤其是红三旱地区相对成熟较早。其次,柴西新生界烃源岩最早成烃期应在晚始新世,红三旱三号地区可能更早,主成烃期应在中新世-更新世期间。 根据确定的主要成藏期,进一步分析各个主要成藏期的沉积、古构造配位特征,通过分析认为,柴西地区自古新世路乐河组沉积以来,沉积与古构造在时间和空间上的配位根据其特征可以划分为三个阶段:上油砂山组沉积前,尽管在上干柴沟组沉积时期阿尔金断裂发生自晚白垩世以来第二次走滑,但柴西地区基本呈现“稳定隆升与沉降,纵向上继承性沉积及横向上大面积坳陷充填”的特征;N2 -Q1+2 沉积时期,下油砂山组沉积后,尽管盆地仍然呈 2坳陷充填的特征,但面积已经开始萎缩,沉积中心开始缓慢地朝北东方向迁移,在东昆仑山与阿尔金山前出现剥蚀现象,柴西地区呈现“不均衡隆升与沉降、山前部分地层遭受剥蚀,相对小面积坳陷充填”的特征;Q3+4以来,结合柴西地区现今构造样式及 Q3+4地层分布可以知道,Q3+4 地层在柴西大部分地区已经被剥蚀掉,柴西地区受到北北东方向强烈的挤压作用,大量呈 NW 向展布的断裂和褶皱构造已经形成,湖岸线基本退出柴西地区,形成现今气候干旱、地表复杂的新局面,油气藏也遭受严重破坏,有名的“油砂山”就是很好的例证,此时期呈现“近南北向挤压,地层变形断裂及地层剥蚀严重”的特征。柴达木盆地位于青藏高原的北端,而柴西地区沉积、古构造这种配位特征呈现的阶段性恰好与青藏高原的隆升活动在时间上耦合。 含油气系统是当前油气地质领域的热点研究课题之一。对盆地划分的各个含油气系统是盆地各个地质历史时期沉积、构造、地热等多个因素演化作用的结果,到目前为止,含油气系统的研究尽管应用了系统的思路,动态、联系、整体的观点,但仅限于对现今盆地内已经形成的油气系统进行划分及对各个要素的研究。而如何去再现盆地各个地质历史时期含油气系统的演化研究还远为不够,对其进行进一步的深入研究和讨论也明显不足。以含油气系统为指导,结合柴西地区主要成藏期的沉积、古构造的配位特征,利用“以结构或结构核划分含油气系统”的思路,并提出“古含油气系统”的概念,将研究区含油气系统的演化分为上干柴沟组沉积前、上油砂山组沉积前、Q3+4 沉积前及今含油气系统四个阶段依次进行含油气系统划分,以达到研究含油气系统的动态演化研究的目更多还原

【Abstract】 Petroleum exploration has had a history of 50 years in the Qaidam Basin since 1954, whichmakes a framework-looking for oil in Jurassic and Tertiary strata in the western part of the basinand for gas in Quaternary sediments. Up to now, the western basin contains 90 percent of theproved reserves of the whole basin. Although much synthetical petroleum geology work has beendone on oil fields such as Youshashan, Shizigou and Huatugou in the west basin, the law of poolforming is still not fully understood, for strong structural movements in the region, which issurrounded by Altyn, Kunlun and Qilian Mountains, led to a complex distribution of reservoirrocks. So detailed studies on allocation between sedimentation and paleostructure in the mainaccumulation time and forecasting perspective plays, by way of many subjects such as basin andpetroleum system analysis, and sequence stratigraphy, will become more and more important inlowering the risk, and increasing the efficiency in the petroleum exploration and economicalbenefit by reducing risks. And they will give proves for selecting prospective plays. In this study we focus on Cenozoic formations, which are in stratigraphic order: PaleoceneLulehe Formation, early Eocene lower part of the Lower Ganchaigou Formation, middle Eoceneupper part of Lower Ganchaigou Formation, late Eocene-Oligocene Upper Ganchaigou Formation,early Miocene Lower Youshashan Formation, late Miocene Upper Youshashan Formation,Pliocene Shizigou Formation and Pleistocene Qigequan Formation. The paper addressespaleocurrent distribution, sedimentary paleogeomorphology and distribution of sedimentary faciesin different stages, which can likewise be separated into (shallow water) fan delta, alluvial fan,diluvial fan, coastal and shallow lake, half-deep lake, alluvial plain and coastal sedimentary facies. By reason of the complex structures in the Qaidam Basin it is not enough to converse the basin’sevolution history only by structure explanation. The research on paleostructures, geometric shapeof sediment filling and distribution of lithofacies in different stages may be a good approach torecognize processes and the dynamics during evolution. The characteristics of the western basinsedimentary response reveal that the region had undergone many different-dynamic crustmovements from the stage of Yanshan to the Himalayan stage, which can be divided into fourstages: 1) strike-slip and extensional rifting during Mesozoic, 2) extensional rifting-depressionduring Paleocene-Miocene, 3) strike-slip and extensional depression in late Eocene-Pleistoceneand 4) extrusion, deflection and strike-slip from the end of Pleistocene on. The Qaidam Basin wentthrough the above four basin-stages, and represent today a complex distorted basin. By analyzing four regional paleostructures which formed before the deposition of the lateEocene-Oligocene Upper Ganchaigou Formation, early Miocene Lower Youshashan Formation,late Miocene Upper Youshashan Formation and late Quaternary formation, we know that the wide<WP=9>area whose “axial cord” is located in Shizigou-Third Hongsanhan, which is concordantwith thedevelopment of the depression center since Paleocene, indicating large-scale and strongnorth-northeast shape changes such as extruding and deflecting folds, and thrust faults. However,the main dynamic mechanisms of the basin’s evolution were extensional rifting-depression anddepression. The western basin displays many accumulation times. Distinct source rocks show inconsistentcharacteristics in extent and time of thermal degradation between the different structural units, dueto the differences of the conditions during deposition, and tectonic subsidence. In front of Altynand Kunlun Mountains source rock maturation occurred late, compared with eastern and westernbasin parts, such as the Third Hongsanhan. The earliest maturation stage of source rock in thewestern Qaidam Basin is believed to be late Eocene, while for the Third Hongsanhan’s, it sh更多还原