盐丘构造成像速度建模及逆时偏移关键参数优选

摘要

针对盐下构造，建立合适的速度模型分析流程是实现逆时偏移高精度成像的前提，选择合理的逆时偏移参数是改善成像效果的关键问题。笔者将单一沿层速度建模方法作了相应改进和调整，采用三步法进行速度建模，提高了盐丘内的速度分析精度，盐丘翼部形态得到了较好的表达。利用三步法的建模结果作 RTM 偏移成像试验，消除了盐下出现的假构造，使盐下小幅度构造背斜细节得到准确成像，实现了对盐丘边界及盐丘侧翼的准确归位。模型试验证明，三步法建模方法适用于复杂盐丘构造的速度建模。同时，在建模精度提高的基础上，针对逆时偏移流程中的子波主频、偏移孔径以及偏移网格关键参数作了分析研究，通过西非地区的实际资料试验，对比成像结果的质量，优化参数，消除了由于参数选取不合理而造成的陡倾角成像不准、信噪比降低、数值频散、浪费计算资源等问题的影响，实现了复杂盐丘构造的高精度成像。%The formulation of a proper velocity analysis flow is a prerequisite for implementation of high⁃precision reverse time migration (RTM),and the choice of migration parameter influences the image result directly as well.Traditional means usually construct a velocity model by interpolating along the layer.The author introduced a 3⁃step method to construct a more accurate velocity model,and applied it to field data for migration.The result indicates that this 3⁃step method is capable of eliminating the fault structure and obtaining more re⁃liable image especially for the detailed structure of the salt dome.Besides,the migration parameters are discussed in this paper,including the main frequency of the wavelet,the migration aperture and the grids size for migration.The test in northern Africa shows that the opti⁃mization of those parameters helps reduce the problems of inaccurate image,low S/ N,numerical dispersion and high computational cost, thus achieving accurate salt dome imaging.