垂直入射假设对井旁地震道子波提取的影响及改进措施

子波提取是波阻抗反演的关键技术。通常采用的子波提取方法是利用测井资料求得反射系数,然后与井旁地震道进行反褶积,提取地震子波。这种方法的前提是假设地震波垂直入射于反射界面,而实际地震资料采集时,地震波并非垂直入射于反射界面,反射系数存在随炮检距变化的关系。这样垂直入射假设下的反射系数,就与真实的反射系数存在较大差异。经正演模型试算,在中等炮检距的情况下,垂直入射假设下的反射系数与精确的反射系数之间不仅存在幅值的差异,甚至会出现极性反转。这种差异必然会导致子波提取、波阻抗反演以及地震解释等产生较大误差。为提高精度,必须摒弃垂直入射假设,采用倾斜入射的观点和方法,重新推导反射系数的递推公式。经模型试算,效果较好。

EFFECT OF WAVELET EXTRACTING WITH A SEISMIC TRACE NEAR WELL BASED ON NORMAL INCIDENCE ASSUMPTION AND ITS IMPROVING METHOD

Wavelet extracting is the essential technique of impedance inversion.A wavelet is generally extracted based on the assumption of normal incidence by the deconvolution of reflectivities obtained from well log with a seismic trace near the well.But actural seismic waves do not always strike a interface normally,and the reflectivities change with offset.Therefore,there must be considerable differences between the reflectivities obtained and the real ones.In this case,a newly derived recursion formula for calculating reflection coefficient by slope incidence is proposed in this paper,and it could improve the acuracy of wavelet extracting and impedance inversion and seismic interpretation.The result of model calcultion has proved that the accuracy of wavelet extracting and the result of deconvolution have been improved.