鄂尔多斯盆地东北部神木-佳县地区上石炭统本溪组沉积特征

Sedimentary characteristics of Benxi Formation of the upper Carboniferous in Shenmu-Jiaxian area of the north-eastern Ordos Basin

综合研究区钻井岩心资料及东边野外剖面的岩石类型、岩石结构、沉积构造、岩电组合等及1500余口井砂岩、泥岩、灰岩和煤层等岩性厚度及砂地比展布特征,对神木—佳县地区上石炭统本溪组的沉积特征和本1、本2段沉积微相平面展布特征及其演化进行深入研究。结果表明,研究区主要为三角洲和障壁海岸沉积体系,其中三角洲体系主要为三角洲前缘亚相,可进一步划分为水下分流河道和分流间湾微相;障壁海岸体系可划分为障壁岛、潮坪和潟湖3种亚相,进一步划分为砂坪、泥坪、滨海沼泽等多种微相。研究区西部本2及本1段发育澙湖障壁岛沉积,障壁岛均呈零星状分布;研究区东部本2期主要为潮坪沉积,潮坪沉积以泥坪和砂坪为主,仅北部存在三角洲前缘沉积且规模较小;到本1期演化为三角洲前缘沉积,具有明显的南北分带特征:双山—双99井以北为河控三角洲,西南部则为潮汐改造三角洲。西南部潮汐改造三角洲受潮汐改造程度高,岩石粒度较粗,岩屑及胶结物含量较高,因此粒间孔、岩屑溶孔及晶间孔含量较高,储层物性较好,天然气产量较高。

The Sedimentary features of Benxi Formation of the upper Carboniferous in Shenmu-Jiaxian area and the distribution pattern of sedimentary microfacies and evolution of the Section One and Section Two were studied in depth based on the comprehensive analysis of the rock type,rock texture,sedimentary structure,rock electric and the thickness and the exhibition features of sandstone,mudstone,limestone,coal seam and ratio of sand and stratum of 1500 wells.The results show that the delta and barrier coastal sedimentation systems dominate the study area.The delta system is primarily composed of delta front subfacies,which are further divided into underwater diversion channel and diversion bay microfacies.The barrier coastal system is divided into three subfacies:barrier island,tidal flat,and lagoon,which are further subdivided into various microfacies,such as sand flats,mud flats,and coastal marshes.Lagoon-barrier islands are developed in the west of the study area in Section Two and Section One of the Benxi Formation and the barrier islands distribution are sporadic.In the eastern part of the study area,tidal flat deposits is the main Sedimentary subfacies in Section Two of the Benxi Formation,which include mud flat and sand flat mainly,and only a small scale delt front developed in the north of the study area.But in section one of the Benxi Formation,the tidal flat evolved into delta front which with a distinct north-south zoning features.The sedimentary facie is delta controlled by river in north of Shuangshan-Shuang 99 well,and the sedimentary facie is tidal modification delta in southwest of Shuangshan-Double 99 well line.Because of the high degree of tidal modification,the rock of modification delta in southwest are coarse granularity and higher content of rock debris and cement,therefore,the reservoir is more physical property and higher natural gas production because it had higher content of intergranular hole,debris dissolution hole and intercrystalline pore.