筠连地区上二叠统乐平组层序地层及沉积相研究

Study on Sequence Stratigraphy and Sedimentary Facies of the Upper Permian Leping Formation in the Junlian Area

四川南部筠连地区乐平组煤层气资源储量大,勘探程度总体较低,制约了煤及煤系气资源的开采。煤层聚集、砂岩储层展布受控于沉积相及层序地层格架控制。为探究研究区内煤层发育特征及煤层聚集的沉积控因,以钻井和岩心资料为基础,利用层序地层学原理,识别出区内乐平组发育的Ⅲ级层序界面并划分层序,构建层序地层格架;厘清研究区含煤地层名称;利用岩相标志及测井响应特征进行地层对比、单井沉积相划分及连井沉积相对比,明确沉积相在各层序内的发育特征。结果表明,研究区乐平组共存在四个层序界面,依据四个层序界面划分出三个Ⅲ级层序。以测井响应特征为主体,共识别出两类沉积相,五类沉积亚相及九类沉积微相。第一层序(SQ1)和第二层序(SQ2)主要发育河流相,第三层序(SQ3)发育潮坪相。在剖面上,整体表现为由河流相至潮坪相的演化特征;自西向东体现为河流-潮坪-潟湖相的演化趋势。

Junlian area in southern Sichuan has a large reserve of coalbed methane resources in the Leping Formation,and the overall exploration level is relatively low,which restricts the extraction of coal and coalbed methane resources.The accumulation of coal seams and the distribution of sandstone reservoirs are controlled by sedimentary facies and sequence stratigraphic framework.To explore the development characteristics of coal seams and the sedimentary control factors of coal seam accumulation in the research area,on the basis of drilling and core data,using the principle of Sequence stratigraphy,the third-order sequence boundary developed in the Leping Formation in the area is identified and the sequence is divided to build the sequence stratigraphic framework;Clarify the names of coal bearing strata in the research area;Using lithofacies markers and logging response characteristics for stratigraphic correlation,single well sedimentary facies division,and well connected sedimentary facies comparison,to clarify the development characteristics of sedimentary facies within each sequence.The results indicate that there are four sequence boundaries in the Leping Formation of the study area,and three third-order sequences are divided based on these four sequence boundaries.Based on the logging response characteristics,two types of sedimentary facies,five types of sedimentary subfacies,and nine types of sedimentary microfacies were identified.The first sequence(SQ1)and second sequence(SQ2)mainly develop fluvial facies,while the third sequence(SQ3)develops tidal flat facies.On the profile,the overall manifestation is the evolution characteristics from river facies to tidal flat facies;The evolution trend from west to east is reflected in the river tidal flat lagoon facies.