VSP资料的单向隐式差分逆时偏移

REVERSE TIME MIGRATION OF VSP DATA BY UNILATERAL IMPLICIT DIFFERENCE

1. 四川石油研究院;2. 西南石油学院

1. Sichuan Petroleum Research Institute;2. Petroleum Instituee, Southwestern China

根据波动方程的对称性,采用逆时偏移方法对VSP资料作处理,可在上、下行波的交点处成像,完成对反射层的正确归位。逆时偏移有三个部分:(1)成像时间的求取;(2)记录波场外推;(3)反射层成像。 求解波动方程的显示差分格式受到稳定条件的严格限制,而隐式差分格式面临巨大的工作量。本文采用单向隐式差分格式,用追赶法求解差分方程,既满足方程的绝对稳定的要求,又使方程求解简单、运算量小,为求解声波波动方程找到了一条新的途径,也是作VSP资料偏移的一种有效力方法。

Based on the symmetrlzation of wave equation,by using the reverse time migration for VSP data processing,it is possible to image at the point where the upgoing and the downgoing waves intersected. In this way,the reflector could bemigrated to its original position. There are three steps which should be adopted in reverse time migration;(1)the extraction of the time for imaging;(2)the extrapolation of the recorded wavefield;(3)the image of reflector.The solution of wave equation is stfictly confined by limitations of steady conditions when explicit difference format is adopted,or it will be faced with a large quantity of work of time consuming if the implicit difference format is used. In this paper, the solving-of difference equation is by using the unilateral implicit difference format through pursuit technique. As a matter of fact,it not only answers the requirements of "ABSOLUTELY STEADY",but it also makes the extraction of solution easier and simpler,and the operation can thus become very time-saving. In this respect,it certainly opens a new way for solving the wave equation and provides an effective method for VSP migration.