鄂尔多斯盆地中东部本溪组砂体成因类型及发育模式

Genetic Types and Development Models of Sand Bodies of the BenxiFormation in the East-Central Ordos Basin

鄂尔多斯盆地中东部本溪组蕴藏着丰富的天然气资源,具有较好勘探开发潜力,但沉积环境复杂,砂体横向变化快、气藏连续性差,成因不明确,探讨这一时期内的砂体成因类型及发育模式对于该地区油气勘探及古地理重建提供有益的参考和借鉴。在野外露头和岩心观察的基础上,结合岩石薄片、粒度分析以及测井资料分析,系统开展了本溪组岩相及岩相组合特征研究,讨论本溪组砂体成因类型,揭示砂体展布规律与沉积演化过程,建立了本溪组的沉积模式。鄂尔多斯盆地中东部本溪组沉积期发育12种岩相类型。砂体成因类型主要为水下分流河道、潮道、潮坪(砂坪—混合坪)、潮汐砂坝、障壁砂坝、潮汐风暴—陆棚6种。其中,湖田段沉积期,华北板块南北两端处于小陆块初始碰撞拼接阶段,物源供给弱,不发育砂体;畔沟段沉积期,海平面快速上升,研究区东部地区被海水覆盖,南北物源体系进入盆地后,受到以大潮差背景为主的潮汐作用改造,砂体类型主要为潮汐砂坝砂体,同时发育小规模的水下分流河道砂体、潮道砂体和潮坪(砂坪—混合坪)砂体;晋祠段沉积期,南、北两个方向的造山作用增强,其中研究区北部物源供给充足,发育三角洲体系,三角洲砂体往盆内不断进积,发育规模较大,但受到以中小潮差背景为主的潮汐作用改造,以水下分流河道砂体为主,中南部受到以大潮差背景为主的潮汐作用改造,主要发育潮汐砂坝砂体,西部临近中央古隆起水体相对较浅,受到了以中小潮差背景为主的潮汐作用改造,发育障壁砂坝砂体、潮道砂体和潮坪(砂坪—混合坪)砂体。

The Benxi Formation in the central and eastern part of the Ordos Basin is rich in natural gas resources and has exploration potential,but the sedimentary complex sand body changes laterally,the continuity of fast gas reser⁃voir is poor,and the origin is unclear.Discussion on the genetic types and development of sand bodies in this period provides a useful reference for oil and gas exploration and paleogeographic reconstruction in this area.Based on field outcrop and core observations,combined with rock thin section grain size and logging data,the lithofacies and litho⁃facies association characteristics of the Benxi Formation are studied,the genetic types of the sand bodies from the Benxi Formation are discussed,the distribution law and sedimentary evolution of sand bodies are revealed,and the sedimentation of the Benxi Formation is established.The study shows that there are 12 lithofacies types in the Benxi Formation in the central and eastern Ordos Basin during the sedimentary period.There are six genetic types of sand bodies:underwater distributary channel,tidal channel,tidal flat(sand flat-mixed flat),tidal bar,barrier bar,tidal storm,and shelf.Among them,the north and south ends of the North China Plate were in the initial collision and splicing stage of small landmasses during the sedimentary period of the Hutian section,and the provenance supplied weak and undeveloped sand bodies.The eastern part of the study area was covered by seawater,and the north-south provenance system basin was reformed by the tidal action mainly based on the spring tide differences.The sand bod⁃ies are mainly tidal bar,small-scale underwater distributary channel,tidal channel,and tidal flat(sand flat-mixed flat)sand bodies.During the sedimentary period of the Jinci section,the orogeny in the north and south was en⁃hanced.In the north of the study area,the source supply was sufficient,and the delta system was developed continu⁃ously into the basin.The delta sand body was reformed by tidal action dominated by medium and small tidal range background,but it was mainly reformed by the underwater distributary channel sand body in the south-central part,mainly developed tidal bar sand body in the west,which was relatively shallow near paleowater body,and was re⁃formed by tidal action dominated by medium and small tidal range background.Barrier ba,tidal channel,and tidal flat(sand flat-mixed flat)sand bodies were developed.