复杂环境扇三角洲沉积结构探地雷达精细探测技术研究

Study on fine GPR detection technique of fan-delta sedimentary structure in a complex environment

以冲积扇、扇三角洲为主的粗粒沉积扇体规模庞大、体系多样、生储盖配置良好,蕴含巨大勘探潜力。以往主要通过观察露头、分析岩心、测井和地震勘探等方法研究扇三角洲的沉积结构与演化规律,存在获取地下信息不连续、效率低和分辨率低等问题。利用探地雷达可进行快速、高分辨率连续探测,有助于精细解剖扇三角洲浅部沉积特征。文中利用探地雷达对青海希里沟湖扇三角洲内部结构进行探测,通过野外采集实验,分析数据特征和属性,阐明复杂环境对探测结果的影响,提出复杂环境下探地雷达精细探测的最优野外数据采集方案。同时,针对数据中道间距不一致、同相轴交叉和地形起伏等问题,提出距离归一化、偏移和静校正三个关键处理手段。实现了水道和坝体边界亚米级精度的定位,给出了水道和坝体的尺寸信息,阐明了洪水对扇三角洲储层结构的影响,为后期埋深数千米的古代扇三角洲储层建模提供了必要的精细构型组合规律和定量地质信息。

The coarse-grained sedimentary fans mainly composed of alluvial fans and fan deltas are large in scale and have diverse systems,good source-reservoir-cap rock configuration,and great exploration potential.In the past,the sedimentary structure and evolution laws of fan deltas were studied by methods including observation of outcrops,core analysis,well logging,and seismic exploration,but these methods faced problems of discontinuity as well as low efficiency and resolution in obtaining subsurface information.Ground-penetrating radar(GPR)can be used for rapid,high-resolution,and conti-nuous detection,which is helpful for fine dissection of shallow sedimentary characteristics of fan deltas.Therefore,this paper used GPR to detect the internal structure of the Xiligou Lake fan delta in Qinghai Province,and through field acquisition experiments and analysis of data characteristics and attributes,the influence of a complex environment on detection results was clarified.Then,the optimal field data acquisition scheme was put forward for the fine GPR detection of shallow sedimentary structure of the fan delta in a complex environment.Moreover,three key processing methods,i.e.,distance normalization,migration,and static corrections,were proposed to solve the problems of inconsistent trace intervals,event crossing,and topographic relief.As a result,the scheme of high-resolution and fast detection technology for the internal structure of the fan delta is formed.The boundary positioning of channels and dams is realized in submeters,and the size information of channels and dams is provided quantitatively.The influence of floods on the structure and quality of fan delta reservoirs is clarified.The result provides the essential fine architecture combination laws and quantitative geological information for later studies of the modeling of ancient fan-delta reservoirs with a burial depth of several thousand meters.