南图尔盖盆地SA区块河道砂体演化及定量刻画

Evolution and Quantitative Delineation of Fluvial Channel Sandbodies in Block SA of the South Turgay Basin, Kazakhstan

针对河道砂体横向变化快而难以有效刻画评价的问题,综合应用分频检测、相位调整、地层切片及地质体雕刻等技术对南图尔盖盆地SA区块上侏罗统阿克萨布拉克组河道发育特征及期次进行了研究。首先,利用分频方法检测出目的层段可能存在的两期调谐厚度不同的河道沉积体;然后,采用波阻抗分析和90°相位转换,揭示目的层段地震负振幅与河道砂岩具有较好的对应关系;最后,在高频层序地层格架内制作等时地层切片的基础上,通过河道沉积特征及典型地层切片振幅的单井标定分析,识别并分期刻画出两期不同类型的河道砂体。结合河道弯度、宽厚比及储集体积等参数综合分析认为,早期河道具有低弯度曲流河特征,晚期河道为具有平直河特征的三角洲平原分流河道,且早期河道储集体积明显高于晚期河道。

Effective delineation and evaluation of fluvial channel sandbodies are impeded by their rapid lateral variations. In this study, frequency detection, phasing, stratal slicing, geological engraving, and other techniques were comprehensively applied to study the characteristics and duration of channel development in the Upper Jurassic Akshabulak Formation, located in Block SA of the South Turgay Basin. First, the possible existence of two stages of channel sedimentary bodies with different tuning thickness was detected within the target segment using the frequency-division method. Next, wave impedance analysis and90° phase conversion revealed relatively good agreement between the seismic negative amplitude of the target segment and channel sands. Lastly, based on a high-frequency sequence stratigraphic framework, two types of channel sands from different stages were identified and delineated using isochronous stratal slicing; single-well calibration analysis of the characteristics of channel sedimentation were combined with the amplitudes of typical stratal slices. A comprehensive analysis of various parameters, including channel sinuosity, width-thickness ratio, and reservoir volume, suggests that the early-stage channel had characteristics of a meandering river with low sinuosity. In contrast, the late-stage channel was a delta plain distributary channel,with the characteristics of a flat, straight river. In addition, the channel had a significantly higher reservoir volume in the early stage compared to the late stage.