炮道密度与观测系统的变化及对地震成像影响的探讨

在前人研究的基础上,完整地导出了面元大小和覆盖次数、炮点子域和排列片接收道数以及接收点子域和排列片总炮数等参数与三维炮道密度的基本关系,阐述了炮道密度的物理意义。讨论了一定条件下,随面元大小、炮点子域和接收点子域变化的三维观测方式及其属性的变化规律。基于YA三维和SHB三维实际资料,对比分析了不同观测方式的地震成像效果,总结了影响地震剖面品质的关键观测系统参数。研究认为,以面元为单位面积的炮道密度等同于面元的有效覆盖次数。一定炮道密度条件下的三维观测方式是多变的,对三维观测系统参数的具体描述是炮道密度应用的基础,而覆盖次数和炮点密度是影响地震成像的两个重要参数,高覆盖有效提高了剖面的信噪比;相同覆盖次数条件下,较高的炮点密度(DS/DR∝1)和均匀分布的炮检点,面元能获得更高的近中偏移距覆盖次数,方位角分布更均匀,利于缝洞储集单元及断层边界的准确成像。

 On the basis of the previous studies,the basic relations between the three-dimensional (3D) shot and trace (S&T) density and the parameters such as the bin size,fold,shot compartmentation and the number of traces of receiving patch,the receiver compartmentation and total number of receiving patches were calculated,and the physical meaning of the S&T density was analyzed.The design of the 3D survey geometry and its properties were discussed in terms of bin size,shot compartmentation,and receiver compartmentation for a given S&T density.Using actual 3D data from YA and SHB,the seismic imaging results using different 3D survey geometries were compared,and the key parameters of geometry that affect the quality of seismic data were determined.It was concluded that S&T densities per unit bin correspond to the effective fold of the bin.Several possible 3D geometries are available for a given S&T density.Determining the parameters of the 3D survey geometry is essential for the application of S&T density.Among these parameters,fold and shot density are the most important factors that affect seismic images.A higher fold can effectively enhance the signal-to-noise ratio of a section.For a given fold,a higher shot density and uniform distribution of shot-receiver points can help obtain higher folds for near and medium offsets in a bin.The resulting distribution of the azimuths is also more uniform,which is conducive for achieving an accurate image of fracture-cave reservoir units and fault boundaries.