塔里木盆地西北缘露头区奥陶系古溶洞地质建模

Paleocave geological modeling in the Ordovician outcrops,Northwest Tarim Basin

塔里木盆地西北缘奥陶系大型古溶洞广泛出露，为古溶洞露头地质建模提供了优越的条件。综合野外资料和 Google Earth 影像分析，将大型古溶洞以形态结构特征为依据划分成管道—厅堂连通型溶洞、单一管道孤立型溶洞、流线型溶洞3种类型；以存在形式划分成单一溶洞和溶洞群。其中，管道—厅堂连通型溶洞以潜流带型为主，在平面上沿主方位通过岩溶管道连接厅堂分布，厅堂大小不等，在50～50000m 3之间变化；单一管道孤立型溶洞以渗流带型为主，平面上呈现单一管道线条状；流线型溶洞分布在潜流带中，从剖面上看呈近圆形、椭圆形和豆荚状等多种形状，包括顺层和斜交地层2种类型。结合各露头剖面中构造、地层条件及发育溶洞类型，明确管道—厅堂联通型溶洞受不整合面控制，分布在三间房、五道班和西克尔剖面中；单一管道孤立型溶洞受断裂系统控制，分布在一间房和硫磺沟剖面中；流线型溶洞主要分布在西克尔剖面，沿溶蚀沟道两侧分布；多种不同因素的耦合控制了溶洞群的分布。以此建立了综合大型古溶洞特征及其控制因素的古溶洞发育概念地质模型，以溶洞群为主要体积计算单元，通过与塔北奥陶系串珠进行体积对比，明确了地质模型的油气勘探意义。

Paleokarst outcrops largely occurred in Northwest Tarim Basin,which provided a good condition for paleocave geological modeling.Combined with outcrop research and Google Earth image,on basis of karst morphology and paleocave architecture characteristics,the large paleocaves could be divided into pipe-hall connected paleocave,single pipe isolated paleocave and streamlined paleocave.There are single paleocave and paleocave group according to their existing forms.Pipe-hall connected paleocave is＆nbsp;mainly located in phreatic zone,and its shape contains single lines type,single paleokarst channel type and pipe-hall.The size of hall varies from 50m 3 to 50000m 3 .Single-pipe-isolated paleocave is mainly lo-cated in vadose zone,and the shape on section can be circular,ellipse,etc.,but the shape on tabular surface is single-streamed pipe.The extending lengths of caves are controlled by the fracture principal ori-entation.Streamlined paleocave is also located in phreatic zone,distributing along and /or across the stra-ta.Their shape on section is circular,ellipse,lageniform,etc.With the analysis of outcrop structural characteristics,stratigraphic conditions and cave types,we find that pipe-hall connected paleocave is mainly affected by the weathering crust unconformity,and is mainly distributed in Sanjianfang,Wudao-ban and Xekar Sections.Single-pipe-isolated paleocave is mainly controlled by unconformity,and distrib-utes in Yijianfang and Liuhuanggou Sections.Streamlined paleocave mainly distributes along both sides of the eroding channel in Xekar Section.Distribution of paleocave group is controlled by various factors. Based on characteristics of large caves and their main controlling factors,a paleocave geological model was proposed.In order to give a guide for forecast of paleokarst reservoir distribution in covering area,the bulk of paleocave group was computed comparing with the volume of “light dot” in North Tarim Basin.