低勘探程度盆地速度特征分析与大尺度成图方法及其应用——以西非毛塞几比盆地为例

以西非毛塞几比盆地为例,介绍了盆地演化与地层结构特征,总结了盆地裂陷后期宏观地层速度特征,剖析了影响盆地速度分布的因素。研究表明:盆地地层速度具有平面上“西北深水区低,东南陆架区高”、纵向上“两段式”的分布特征,而影响盆地速度分布的主要因素是埋深和压实作用、地层岩性组成、地层地质年代厚度组合关系等。鉴于毛塞几比盆地面积广、无连片三维地震、井震资料有限、多种三维速度建模方法适用性差的现实情况,提出了利用分区井控插值与变速拟合剥层法构建层速度模型的方法,首先基于地震解释方案,通过纵向分层、横向分区构建速度模型单元,然后利用井速度插值或变速拟合方法进行模型速度赋值,最后经剥层计算实现盆地尺度的变速成图。利用大尺度时深转换成果实现了从宏观角度对该盆地横向构造、地层变化规律更准确的认识以及对该盆地烃源灶更可靠的预测,同时也实现了快速发现和落实盆地深水、陆架坡折带构造圈闭的目标。为低勘探程度盆地大尺度变速成图提供了借鉴。

 With the MSGBC basin in West Africa chosen for a case study,the basin evolution and stratigraphic structure characteristics thereof were elucidated,the macroscopic features of the formation velocity were analyzed,the characteristics of the formation velocity distribution during the basin drift stage were summarized,and the key factors influencing the velocity distribution were analyzed herein.The results show that the MSGBC basin is characterized by a laterally low formation velocity in the northwest deepwater region,which becomes high in the southeast shelf region.In the vertical direction,the formation velocity is characterized by two stages.The following key factors were found to influence the velocity distribution:burial depth and compaction,formation lithology,combination of geological era,and formation thickness.Considering that the MSGBC basin covers a wide area,does not have a succession of three-dimensional (3D) seismic data,has limited and sparse well logging and two-dimensional seismic data,and various 3D velocity model building methods are inapplicable,a zonal well-controlling interpolation and variable-velocity fitting stripping method was proposed to construct the interval velocity model.Based on the seismic interpretation,vertical unitization and lateral zonation were employed to build the velocity model unit.Moreover,well velocity interpolation or the variable velocity fitting method was used to establish the model velocity.Subsequently,after stripping of the calculation,basin-scale variable-velocity mapping was performed.From the results of the large-scale time-depth conversion,a more accurate understanding of the lateral structural and stratigraphic patterns of the basin was achieved,and the hydrocarbon source kitchen of the basin was predicted more reliably.This improved understanding can facilitate a rapid search of structural traps in the deep water and shelf-slope break zones of the basin.This research therefore provides an important reference for large-scale variable velocity mapping in a low exploration maturity basin.

国家科技重大专项(2017ZX05032-002)资助。