准噶尔盆地玛北地区三叠系百口泉组沉积模式

Depositional model of the Triassic Baikouquan Formation in Mabei area of Junggar Basin

准噶尔盆地西北缘玛北地区三叠系百口泉组储层发育于扇三角洲沉积环境,岩石类型复杂,储层的储集性能主要受不同沉积微相下岩性相的控制,然而沉积微相与岩性相之间的匹配关系复杂。因而,建立沉积微相与岩性相相匹配的沉积模式对该区储层主控因素的研究及储层预测具有重要意义。通过岩心精细观察、薄片鉴定、测井及录井资料分析,结合研究区沉积背景和构造环境,在强调岩性相和沉积微相之间的配置关系并考虑沉积物的粒度、颜色、沉积构造、沉积微相及经历的成岩作用等特征的基础上,划分了11种主要的岩性相类型:水上泥石流砾岩相、水下主河道砾岩相、辫状河道砂砾岩相、水下河道砂砾岩相、水下泥石流砂砾岩相、平原河道间砂泥岩相、水下河道间砂泥岩相、水下河道末端砂岩相、河口坝-远砂坝砂岩相、前扇三角洲粉砂岩相和前扇三角洲泥岩相。在岩性相特征、剖面岩性相及剖面沉积相特征研究的基础上,结合沉积序列、沉积结构和沉积构造等特征,建立了能够反映研究区主要沉积环境及沉积特征的沉积微相与岩性相相匹配的沉积模式。在此基础上,研究了三叠系百口泉组各段沉积微相与岩性相相匹配的平面展布特征。百口泉组3个段在研究区主要发育扇三角洲平原及前缘亚相。其中,百一段扇三角洲平原主要发育砾岩相,扇三角洲前缘主要发育砂岩相;百二段下部扇三角洲平原主要发育砾岩相,扇三角洲前缘以砂岩相为主、砂砾岩相为辅;百二段上部扇三角洲平原以砾岩相为主、砂砾岩相为辅,扇三角洲前缘以砂岩相为主、砂砾岩相为辅;百三段扇三角洲平原以砂砾岩相为主、砾岩相为辅,扇三角洲前缘以砂岩相为主、砂砾岩相为辅。

Reservoirs in the Triassic Baikouquan Formation in Mabei area of northwest margin of Juggar Basin were deve-loped in a fan delta setting,in which the rock types are diversified,the lithologic facies under different sedimentary micro-facies played vital role in controlling reservoir properties,and the matching between sedimentary microfacies and lithologic facies was complex.Thus establishing depositional models with matching sedimentary microfacies and lithologic facies is of great significance in studying the main controlling factors of reservoirs and prediction of reservoirs.Based on a combi-nation of analyses of core observation,thin section and log data,with sedimentary background and tectonic settings of the study area,we focused on the configuration relationship between the lithologic facies and sedimentary microfacies and took into consideration the granularity and color of sediments,sedimentary texture and microfacies,and diagenesis.The results shows that 11 main lithologic facies types can be recognized in the study area：superaqueous mudslides conglomerate faci-es,subaqueous channel conglomerate facies,braided channel coarse-clastic facies,underwater channel coarse-clastic faci-es,subaqueous debris flow coarse-clastic facies, plain interchannel sandstone-mudstone facies, underwater interchannel sandstone-mudstone facies, underwater channel-end sandstone facies, mouth bar-distal sandbar sandstone facies, frontal fan-delta siltstone facies,and frontal fan-delta mudstone facies.A depositional model with matching sedimentary microfa-cies and lithologic phase was also established based on lithologic facies characterization,profile analyses of lithological nbsp;facies and sedimentary facies,as well as sedimentary sequence,depositional texture and sedimentary structure.Then,we studied the planar distribution of the microfacies and lithologic facies in the Triassic Bakouquan Formation.It shows that three members of the Formation contain mainly fan-delta plain and fan-delta front subfacies.The first member developed conglomerate in its fan-delta plain and sandstone in its fan-delta front;the second member grew at its lower part mainly conglomerate in its fan-delta plain and glutenite and sandstone in its fan-delta front;and at its upper part conglomerate with glutenite in fan-delta plain and sand with some coarse-clastic rocks in fan-delta front;and the third member is domi-nated by coarse-clastic facies followed by conglomerate facies in its fan-delta plain,and it is dominated by sandstone faci-es followed by coarse-clastic faceis in its fan delta front.