【作者】 梁积伟；

【导师】 李文厚；

【作者基本信息】 西北大学 ， 岩石学、矿物学、矿床学， 2004， 硕士

【摘要】 鄂尔多斯盆地是位于华北地台西部的大型克拉通叠合盆地，上古生界的含气系统是具有自生、自储、自盖特点的煤成气含气系统。山西组是盆地东北部的重要含气层位，其沉积地层形成于太原期整体海退背景之后的北高南低的缓倾古地形之上，形成厚度稳定、特征鲜明的河流—三角洲相陆源碎屑岩含煤建造。 依据高分辨率层序地层学原理，综合考虑受构造运动、沉积物供应、海平面变化和气候影响的基准面旋回和沉积物的体积分配，对研究区山西组地层进行了高分辨率层序地层的划分。山西组属于晚古生代长期海平面下降旋回中由海到陆的过渡阶段，山西组自身构成一个中期旋回，其上升半旋回由山₂段构成，以多层煤层和沉积向物源方向的退积为特征。下降半旋回由山₁段构成，其沉积以向湖方向的强烈进积为特征。依据垂向组合和旋同特征，如风化剥蚀面、冲刷面、岩性岩相突变面、水道下切、上升到下降或下降到上升的转换面，可以将山西组中期旋回划分为五个短期旋回，SSC1、SSC2、SSC3、SSC4、SSC5，它们分别对应于山₂³、山₂²、山₂¹、山₁²、山₁¹亚段。 从古构造格局、沉积体系的展布、沉积构造、结构、碎屑的成分特征、石英的阴极发光特征、重矿物特征、稀土和微量元素特征诸方面探讨了研究区沉积物的来源。研究表明，山西组的物源来主要自于盆地北部的前寒武纪变质结晶基底，还有一少部分来自于北部及东北部的火山岩，来自沉积岩的源岩很少。 依据剖面露头观察、岩心描述、单井测井相和层序地层分析、连井剖面对比，结合岩矿分析和地球化学的方法，识别出了三角洲沉积体系和河流沉积体系，三角洲沉积体系以三角洲平原和三角洲前缘沉积为主，前三角洲不发育。三角洲平原以分流河道形成骨架砂体，在分流河道之间，发育泥炭沼泽和洼地，以及天然堤和决口扇沉积。三角洲前缘的骨架砂体以水下分流河道的砂体最为发育，也可见残留的河口坝序列，远砂坝和前缘席状砂不发育，在水下分流河道的骨架砂体之间广泛展布分流间湾的细粒泥质沉积。河流沉积体系展布于研究区北部，发育于山西组的早期和晚期，以曲流河沉积为主，辫状河沉积不仅分布范围极其局限，而且发育的时限很短。 应用单因素优势相平面作图的方法，对研究区的各短期旋回进行了砂体厚度等值线图、砂体厚度／地层厚度比值等值线图、煤层厚度等值线图的制作，探讨了储集砂体在空间上的展布特征，以及沉积相和微相的平面展布和空间演化。 沉积相带的展布和地层的垂向组合受控于构造运动、气候、沉积物供应和基准面变化。山西组沉积期受低幅度幕式构造运动的影响，沉积物的供应速率表现出间歇性的特点。由于基底起伏和沉积物供应速率的变化使基准面发生旋回性变化，造成地层结构呈旋回性变化的特点。每个旋回都由上升半旋回和下降半旋回两部分构成。不同的旋回受基准面变化速率的影响，表现出不同的旋回性结构，如山₂³以上升半旋回为主，下降半旋回不发育甚至缺失。同一旋回在不同的地理位置上，由于可容纳空间和沉积物供应速率变化的不同，也表现出不同的旋回结构，如三角洲平原上升半旋回发育，而三角洲前缘则以下降半旋回占主导地位。 通过对宏观上沉积相的展布和微观上影响储层物性因素的分析，认为天然气的富集在宏观上受砂体展布的控制。在微观上，成分成熟度和结构成熟度高，杂基含量少的三角洲前缘水下分流河道砂体是天然气富集的最有利区域。成分成熟度和和结构成熟度稍低，杂基含量略高的三角洲平原分流河道砂体是天然气富集的较有利区域。更多还原

【Abstract】 Ordos basin, which located at the west part of North China platform, is a large-scale superimposed Craton basin. Upper Paleozoic gas-bearing system is coal origin gas-bearing system which have characteristics of self-generation, self-reservoir and self-coverage. Shanxi Formation is important gas-bearing strata, and it was formed on a gentle slope high in north and low-lying in south setting after overall regressive of Taiyuan Formation. Fluvial-delta build-up of terrigenous origin detrital material with steady thickness and distinct characteristics was formed.Based on the principle of high resolution sequence stratigraphy, as well taken into account synthetically base level cycle and volumetric partitioning and facies differentiation controlled by tectonics movement and sediment supply and sea-level change and climate, high resolution sequence stratigraphy division was applied in Shanxi Formation. Shanxi Formation belongs to transitional phase of later Paleozoic long-term base level falling. Shanxi Formation itself makes up mid-term base level cycle, and its ascending half cycle is made up of lower Member of Shanxi Formation, which has the characteristics of several coal-bearing bed and sediment retrogress. The falling half cycle, which has the characteristics of strong transgress towards lake, is composed of upper Member of Shanxi Formation. According to vertical association and cycle characteristics, such as weathering and denudation surface, scour surface, sudden change surface of lithologic character and lithofacies, channel incise, transfer surface between ascending and falling, mid-term cycle of Shanxi Formation can be divided into 5 short-term cycles, namely SSC1, SSC2, SSC3, SSC4, SSC5 in ascending order.From palaeo-structure pattern, distribution of sedimentary system, depositional structure and texture, composition characteristics of debris, cathodoluminescence of quartz, characteristics of heavy minerals, characteristics of rare earth element and trace element, sediment source of study area was discussed. It indicated that debris material of Shanxi Formation mainly derived from pre-cambrian metamorphic rock from the north part of Ordos basin, there is also a little portion of debris come from volcanic rock from the north and northeast part of the basin, while debris derived from sedimentary rock is even less.Based on outcrop observation, core description, single well-log and sequence analysis, connecting-well section, combined with lithological and mineralogical analysis and geochemical method, delta system and fluvial system were identified. Delta system is mainly composed of delta plain and delta front, while pro-delta is not well developed. On delta plain, distributary channel forms framework sand bodies. Between distributary channel, peat swamp and pit, as well as natural levee and crevasse splay are developed. Framework sand bodies of front delta is sub-aqueous distributary channel, while mouth bar and distal bar and front sand sheet are not well developed or preserved. Fine grain sediment of distributary bay is spread widely between sub-aqueous distributary channels. Fluvial system is distributed at the north part of the study area, developed during early and late period of Shanxi formation. Fluvial system is dominated by meandering river, while braided river is not only confined within small area, but short time as well.Appling the method of cartography with single factor and dominance aspect, we have drawn contour line map of sand thickness, contour line map of ratio between sand thickness and stratum thickness, contour line map of coal thickness in each short-term cycle. We discussed distribution characteristics of reservoir sand body and evolution of sedimentary facies and microfacies.Distribution of depositional facies zone and vertical association is controlled by tectonic movement, climate change, sediment supply and base level variation. Shanxi Formation is strongly affected by low amplitude episode tectonic movement. The rate of sediment supply has the feature of intermittence.更多还原