Acquisition, Processing and Interpretation of a Western Delaware Basin 3D VSP
Jay S. May (Concho), Brian Fuller (Sterling Seismic), James Caputo (Concho)
Zero offset VSP’s have been in everyone’s tool box for many years. They provide an unrivaled seismic-to-well tie and a very well sampled time-to-depth function. However, the image is just around the well bore and we are always wishing we had more data to use. In many exploration areas there is little seismic data available. That is certainly true in the Western Delaware Basin of Texas. Until now the next step following a wildcat and zero-offset VSP would be to perhaps acquire a few new 2D lines (vintage 2D data is often under sampled and has low signal to noise) to try and map the area. The problem is we are often exploring in complex geologic areas so 2D cannot always give a reliable image and overcome surface noise problems. A 3D survey can overcome those problems but now you are going down the expensive and time-consuming path of executing a 3D survey. What if you could use a proven technology that would let you acquire a 3D image around a wellbore out to a distance of several thousand feet for less money and in a time frame of weeks instead of months? The 3D VSP lets you do that. In the example here a one square mile 3D VSP was acquired in less then a week using a 60-level fiber optic tool and 4 vibrators. The image is high resolution (55 Hz and 25-ft CDP’s) and provides a 3D image for less than $450K. A comparable 3D survey would have cost much more due to the small bin size and in this case the rugged terrain.
The economic viability of this 3D VSP survey was made possible through the availability of, what was at the time, new borehole seismic recording technology. The survey would have taken two to three times longer and would have been much more expensive just three months earlier than when data acquisition was done. Rapid turnaround of the data and accurate seismic imaging was made possible through proven, but newer time-domain 3D VSP data processing technology that treats 3D VSP data more like surface seismic data. This technology allows accurate picking of reflection velocities and calculation of true surface-consistent residual statics.
These data certainly show the value of the technology and its’ cost and turnaround make it an excellent tool for prospect development.