Multiple Analysis ? A Borehole Seismic Solution

Abstract

Borehole seismic data acquired on wireline or during drilling have a variety of uses from industry standard corridor stack and sonic calibration to AVO, Imaging, real-time time-depth information and pore pressure prediction. This paper presents a novel workflow that is designed to identify seismic multiple generators using Vertical Seismic Profiling (VSP) data. The primary technique in identification of multiples in surface seismic data is assessment of periodicity and polarity. Similarly the major technique in identification of multiples in VSPs is assessment of the complete VSP wavefield for truncations and periodicities. In both cases these assessments are commonly made using a qualitative approach. Now, a more rigorous and structured approach that involves separation of the multiple energy from the primary energy is presented. This allows easier interpretation and a quantitative assessment of the relative strengths of primary reflections and their multiples, which in turn simplifies the interpretation of the surface seismic data. The results of this analysis is a list of tops and bottoms of major peg-leg multiple generators and an image of upgoing multiples. This VSP interpretation is transferable to the surface seismic data and can be used in surface seismic reprocessing to target specific formations for removal of seismic multiples generated in these formations.