摘要： 玛湖凹陷是准噶尔盆地最具规模的油气聚集带与勘探区,发育以砾岩为主、具有较强非均质性的粗粒沉积复杂地层。对粗粒沉积体的精细刻画有助于研究沉积体内部的非均质性特征。应用储层构型分析法,结合研究区岩心、测井、录井资料,对玛湖凹陷夏子街扇区三叠系百口泉组沉积体内部9个级次构型要素的几何形态、大小、方向以及相互之间的叠置关系进行了表征,识别出12种岩石相类型以及10种由岩石相组合而成的沉积微相类型。通过分析沉积微相在垂向、平面上的不同组合特征,扇体的类型受沉积环境影响发生变化,逐渐由冲积扇、河流扇转换为扇三角洲,整体反映了湖平面上升或沉积物供给量逐渐减小的沉积背景。分析夏子街扇区各期次的扇体特征,包括长轴、短轴距离、长轴短轴比、扇根与扇缘厚度变化、扇体坡度变化、扇体最大粒径变化等,认为扇体顺物源方向有以下变化趋势: 沉积物粒径大小随河道搬运逐渐减小,减小的幅度受扇体坡度影响,坡度越陡沉积物粒径减小的越快;河道数量减少,流量降低;河道沉积物在横向和纵向上的连通性逐渐降低;砂岩、砾岩厚度逐渐减小,泥岩厚度逐渐增加,湖相沉积变得较为发育。总结玛湖凹陷百口泉组的各期次扇体共可归纳出6种扇体模式: 冲积扇、冲积—河流扇、河流—末梢扇、河流扇—扇三角洲、扇三角洲、大型河流扇。

关键词: 玛湖凹陷, 百口泉组, 岩石相, 构型分析, 扇三角洲, 河流扇

Abstract: Mahu sag is the largest oil and gas accumulation belt in the Junggar Basin, and the exploration target is focusing on the complex and highly heterogeneous coarse-grained deposits. To reveal the internal heterogeneity of coarse-grained deposits, we carried detail sedimentary and reservoir architecture analyses (e.g., configuration, size, direction and stacking patterns) by using seismic, core and well logging data from the study area. We have identified 12 lithofacies and 10 sedimentary microfacies that are composed of different combinations of lithofacies Based on the stacking patterns of sedimentary microfacies in vertical and lateral, we have identified 10 vertically stacked fan lobes. Each fan lobes is strongly affected by the depositional environment and has changed from stacked alluvial fans and fluvial fans to fan delta under the influence of overall rise of the lake level and the decreased supply sediment. A detail analysis of the sedimentary characteristics for each phase of fan lobes, including long axis, short axis, long axis and short axis ratio, thickness changes of inner and outer fan, slope gradient and grain size change, shows several progressive changes when fan move downstream: (1) the grain size has become smaller when moving downstream and is controlled by the slope gradient of fan. For example, sediment grain size has reduced significantly in a steep slope. (2) The numbers of channel and water discharge have decreased toward downstream. (3) The connectivity of sedimentary bodies in lateral and vertical has reduced. (4) The thickness of sandstone and conglomerate has become thinner, while the mudstone has become much thicker. The lacustrine deposits become more dominant. In summary, we have recognized six fan models for the Baikouquan Formation in Mahu sag, including alluvial fan, alluvial-fluvial fan, fluvial-terminal fan, fluvial delta-fan delta, fan delta and large fluvial fan.

Key words: Mahu sag, Baikouquan Formation, lithofacies, architecture analysis, fan delta, fluvial fan

中图分类号: 

• P512.2