基于Tesseral2D的水下砂体地震正演计算

基于水下砂层与围岩的波阻抗差异,应用地震波数值模拟软件Tesseral2D建立含有水、粉细砂、砾砂和砾岩的起伏地层模型,在不同的道间距、最小偏移距、子波频率以及不同岩体波速条件下分别对该模型进行正演计算。一般情况下,在震源频率为400 Hz、最小偏移距为5 m、道间距为1 m或2 m时,地震波响应明显、同相轴清晰、干扰波较少,水下地层界面反映良好。进一步结合南京长江第二大桥桥址区的地质资料,建立含有水、淤泥质粉质黏土、粉细砂、砾砂、砂砾卵石和砾岩的水下砂层模型,应用Tesseral2D软件对该模型进行正演研究。结果表明,在震源频率为400 Hz、道间距为2 m以及最小偏移距为5 m时,地震响应能很好地反映水下各岩层界面,特别是能较明显地圈定水下砂层的厚度和分布范围,为实际水下砂体的地震勘探提供理论依据。

Tesseral2D-based earthquake forward simulation of underwater sand strata

Based on the difference of wave impedance between underwater sand strata and rock media, a stratigraphic model of fluctuant strata containing water, fine sand, gravel sand, and conglomerate was established using Tesseral2D software for seismic numerical simulation. Then, the forward calculation with the model was conducted under different channel spacings, least offsets, wavelet frequencies, and wave velocities in rocks. Under normal circumstances with a source frequency of 400 Hz, a least offset of 5 m, and a channel spacing of 1 m or 2 m, the seismic response is significant, with constant phases and less interference waves, which also well reflects the underwater stratum interface. In combination with the geological data from the bridge site area of the Second Nanjing Yangtze River Bridge, a stratigraphic model for underwater sand strata was established, containing water, silty clay, silty sand, gravel pebble, and conglomerate. Forward simulation using Tesseral2D software shows that, with a source frequency of 400 Hz, a channel spacing of 2 m, and a least offset of 5 m, the seismic response can well reflect the underwater interfaces between different rock strata, and determine the thickness and distribution range of underwater sand strata, providing an important theoretical basis for the exploration of underwater sand strata.