非零偏VSP折射效应及井源距选择

REFRACTION EFFECTS IN NONZERO-OFFSET VSP AND THE SELECTION OF SOURCE-WELL DISTANCE

塔里木石油勘探开发指挥部,库尔勒841000

Headquater of oil field exploration and development in Tarim, Kurle 841000

在非零偏VSP观测中,井源距是一个很重要的参数。在一定的地质条件下,过大的井源距会造成某些界面产生的折射波先于直达波到达检波器。本文从模型分析和塔中5井实测非零偏VSP测井z分量原始记录出发,分析了过大的井源距与VSP测井记录初至异常的关系,论述了非零偏VSP测量时避免折射效应的方法及最大井源距的求取方法。

In nonzero-offset VSP surveys, the source-well distance is an important parameter. Under certain geological conditions,excessively larger source-well distance may cause refractions along interfaces to reach geophones earlier than direct arrivals. Based on model analysis and a set of field z-component data obtained from a nonzero-offset VSP in well 5 of Tazhong,this paper investigates the influence of excessively large source-well distance on anomalous first arrivals in VSP data and points out the way the refraction effect in nonzreo-offset VSP is removed. In addition. a method to determine the maximum souce-well distance is presented.