鄂尔多斯盆地东北部山西组层序格架下的砂体成因类型、构型及分布

Genetic types,configurations and distribution of sand bodies of Shanxi Formation in northeastern Ordos Basin

鄂尔多斯盆地山西组沉积时期陆生植物繁盛,为天然气的生成提供了充足的气源,油气的富集受控于岩性和岩相,因此深入探讨山西组砂体构型和砂体展布规律十分必要。为加快天然气的勘探步伐,以层序地层学与沉积学基本原理为指导,通过野外露头剖面、钻井、测井等资料的综合分析,研究了山西组四级层序格架下不同成因类型砂体的特征、构型及展布规律。结果表明:研究区山西组可划分为5个四级层序;砂体类型以辫状河三角洲平原分流河道和辫状河三角洲前缘水下分流河道砂体为主;不同类型的河道砂体具有南北成带、东西分割的特征;砂体构型有垂向叠置型、垂向切叠型和独立型3种类型;四级层序PSQ3~1(相当于山2~3段和山2~2段下部)、PSQ3~2(相当于山2~2段上部)和PSQ4~1(相当于山1~2段)均是天然气勘探的主力层系;大保当、余兴庄、龙镇地区均是天然气勘探的有利地区。该方法和研究结果可为研究区及其类似地区层序地层划分、砂体展布规律研究及有利区带优选等提供参考。

During the sedimentary period of Shanxi Formation in Ordos Basin, terrestrial plants flourished, which provides sufficient gas source for the formation of natural gas. The accumulation of oil and gas is con- trolled by lithology and lithofacies. Therefore, it is necessary to study the configuration and distribution of sand bodies of Shanxi Formation. In order to speed up the exploration of natural gas, guided by the basic principles of sequence stratigraphy and sedimentology, through comprehensive analysis of outcrop section, drilling and well logging data, the configuration and distribution characteristics of different genetic types of sand bodies under the fourth-order sequence framework of Shanxi Formation were emphatically studied. The result shows that the Shanxi Formation in the study area can be divided into five fourth-order sequences. The sand bodies are dominat- ed by distributary channel sand bodies of braided-delta plain and the underwater distributary channel sand bodies of braided-delta front. The plane distribution of channel sand bodies is characterized by north-south zonation and east-west penetration. The superimposed modes of sand bodies are mainly three types, vertical overlap, vertical tangency and independent type. The fourth-order sequences including PSQ3^1 （equal to the Shan 2^3 section and the lower part of the Shan 2^2 section）, PSQ3^2 （equal to the upper part of the Shan 2^2 section） and PSQ4^1（equal to the Shan 12 section） are the main layers of natural gas exploration. Dabaodang, Yuxing Zhuang, Longzhen were selected as favorable exploration areas. The method and results could provide reference for the sequence stratigraphic divi- sion, sand body distribution law research and favorable zone optimization for the study area and similar areas.