准噶尔西北缘玛北地区扇三角洲砂砾岩岩相分类及储集意义

准噶尔盆地西北缘三叠系处于大型逆冲推覆断裂带,盆地边缘同生断裂构造活动强烈,发育砂砾岩为主的扇三角洲沉积体系。通过对玛北地区三叠系百口泉组砂砾岩储层取芯段岩芯观察和描述、岩石薄片、扫描电镜、测井以及储层物性数据的分析,结合砂砾岩岩石构成、层理类型、沉积层序和测井曲线响应特征,对准噶尔盆地西北缘砂砾岩体岩性进行精细刻画,建立岩相模式,划分出同沉积相(微相)相符的11种岩相:其中扇三角洲前缘水下河道砂砾岩相、扇三角洲平原辫状河道砂砾岩相叠置连片展布,是最有利的储集体;扇三角洲前缘水下主河道砾岩相、水下河道末端砂岩相及河口坝—远砂坝砂岩相分布局限,储集性良好,为有利"甜点"区;水上泥石流砾岩相和水下泥石流砂砾岩相与扇三角洲平原和前缘分流河道间储集性较差的细粒砂泥岩相组成百口泉组油藏致密的顶底板;前扇三角洲粉砂岩相和泥岩相可作为良好的区域性盖层。不同的岩相类型及沉积条件提供了准噶尔西北缘百口泉组大规模低渗透岩性油气藏优良的储盖组合及顶底板条件。

Lithofacies Classification of Glutenite in the Fan Delta of the Mabei Area in the Northwestern Junggar Basin and Its Reservoir Significance

The northwestern margin of Jungar Basin was located within the large-scale thrust-nappe structures during Triassic period and the margin of the basin experienced intense syn-sedimentary faulting, resulting in the formation of glutenite fan delta. Based on cores observation and decription, thin sections identification and SEM observation, loggin, and physical property data of glutenite reservoir in the Mabei area, lithoglical compositions, layer types and sedimentary sequences of glutenite were discussed in detail to establish the lithofacies model. This study identified 11 glutenite lithofacies: Glutenite facies of underwater channel in the fan delta front and superimposed large-scale braided channel glutenite facies of fan delta plain are most favorable reservoir facies; conglomerate facies at estuary subaqueous distributary channel, sandstone facies at the end of the underwater channel and sandstone facies at estuary-distal sandbar are of limited distribution and regarded as the favorable "sweet spot" area due to their good reservoir potentiality; superaqueous mudslides conglomerate facies, subaqueous mudslides conglomerate facies, and poor accumulation fine-grained sediments deposited at fan-dalta and front stream jointly constituted tight roof and floor of the Baikouquan reservoir. The siltstone facies and mudstone facies of the frontal fan delta can be regarded as a good regional cap rocks. Diffferent lithofacies and sedimentary conditions have provided favorable reservoir-cap assemblages and roof-floor conditions for large-scale low permeability lithological reservoir in the Triassic Baikouquan Formation in the Mabei area.