东海陆架盆地西湖凹陷渐新统花港组年代标尺及层序界面定量识别

Time scale and quantitative identification of sequence boundaries for the Oligocene Huagang Formation in the Xihu Sag,East China Sea Shelf Basin

西湖凹陷是东海陆架盆地中重要的含油气凹陷,近期勘探证实渐新统花港组是当前主力产气层段;截至目前,西湖凹陷花港组层序地层划分方案还存在较大争议,严重制约了砂体等时对比及油气精细勘探进程。依据层序地层学结合天文旋回理论,利用小波变换和INPEFA技术对自然伽马曲线进行数学分析得到小波信号曲线、频谱及INPEFA曲线,建立了西湖凹陷花港组年代标尺及高精度层序界面格架。通过小波变换将GR曲线重构成不同阶次的小波信号曲线和频谱,以异常振动和能量团变化趋势凸显层序界面和旋回信息;同时,利用最大熵谱分析技术对GR曲线进行积分处理获得INPEFA曲线,以拐点和正负趋势定量拾取层序界面和旋回特征,将花港组划分为5套三级层序(自下而上分别命名为SQ_(1)—SQ_(5))。利用频谱分析明确三级层序内部地层叠置旋回,结合小波信号曲线变化特征,可将花港组划分为12套四级层序(自下而上分别命名为H_(12)—H_(1))。花港组GR曲线的多窗口频谱分析结果表明,5套三级层序发育持续时间介于1~3 Myr。通过多尺度多方法融合测井技术对缺少岩心和古生物化石区构建多级次等时层序地层格架具有一定推广意义,为渐新统花港组后期勘探开发提供一定的技术支持。

The Xihu Sag is one of the petroliferous sags in the East China Sea Shelf Basin.Recent exploration has confirmed that the Oligocene Huagang Formation is the major gas pay zone in the sag.However,sequence division of the formation is still in dispute,seriously impeding the isochronous correlation of sand bodies and the fine exploration of oil and gas.Based on the sequence stratigraphy and astronomical cycle theory,the study mathematically analyzes natural gamma curves with wavelet transform and INPEFA(Integrated predication error filter analysis)technology to obtain signal curves,spectrums and INPEFA curves for the establishment of a geologic time scale and high-precision sequence boundary framework for the Huagang Formation.The GR curves are reconstructed through wavelet transformation into different wavelet signal curves and spectrums with the sequence interfaces and cycle information highlighted by abnormal vibration and energy group change trend.At the same time,the maximum entropy spectrum analysis technology is used to integrate the GR curves into the INPEFA curves with sequence boundaries and cycle information highlighted by inflection points as well as positive and negative trends.The Huagang Formation is divided into five third-order sequences(namely SQ_(1) to SQ_(5) from top to bottom).Spectral characterization of strata superimposition and cycles within these sequences are combined with their wavelet signal curves to divide the Huaguang Formation into a total of 12 fourth-order sequences(namely H_(1) to H_(12) from bottom to top).The multi-window spectrum analysis of GR curves shows 1 to 3 Ma development duration for the five third-order sequences.The multi-scale and multi-method integration of logging technology for the construction of multi-order isochronous stratigraphic frameworks in the areas lacking of cores and paleontological fossils is proved to have certain promotional value for the future oil and gas exploration in the Oligocene Huagang Formation of the Xihu Sag.