Vertical Seismic Profile Modelling and Applications for a Deviated Well to Improve Surface Seismic Interpretation

Abstract

Vertical seismic profile (VSP) data is a powerful calibration tool that helps to link the time (surface seismic) & depth domains (well logs). Conventional rig source VSP data is not recommended to be used in a highly deviated well for seismic calibration. Excessive ray bending from the source-receiver offset will cause errors in the vertical time calculations, and this data will not be reliable to calibrate the surface seismic. This paper will discuss a case-study for a highly deviated offshore well using a vertical incident VSP (VIVSP) source geometry. A VIVSP is a unique type of geometry that places the source above the receiver array. This is usually done using a supply vessel for an offshore environment. Placing the air gun source above the receiver ensures vertical raypaths, and this gives the most accurate TWT result. Planning is crucial for this type of VSP to calculate the number of receiver arrays & source positions. 2D ray trace modelling using the surface seismic interval velocity & VIVSP geometry was used to verify the data would be within tolerance for vertical raypaths, and to optimize the acquisition time. VSP data was acquired using the optimized vertical incidence geometry. Data quality was excellent which gave a reliable time-depth profile for most of the well interval. VSP data was processed to corridor stack. and CDP transform was used to create an image below the well trajectory. This data was used to calibrate seismic velocity during seismic processing, as well to tie surface seismic to well.