POSSIBILITIES OF USING VERTICAL GEOPHONE ARRAYS (CVA) IN REFLECTION SEISMOLOGY*

Vertical geophone arrays in boreholes have been used for many years to study seismic velocities by investigating the first arrivals of records. The development of the vertical seismic profiling (VSP) technique shows possibilities of using the reflected events to close the gap between interpretation of conventional seismic data and physical observations made in the well. Reflected events recorded by vertical arrays (as in VSP) generally have higher signal‐to‐noise ratio, larger bandwidth and can easily be separated from multiples. The new Continuous Vertical Array (CVA) technique combines vertical arrays in several boreholes with a line of source points near the surface. The result is a multi‐covered seismic line similar to that of a conventional seismic survey, but it retains the benefits of observations with vertical arrays. The possibilities of the new technique are discussed with the aid of theoretical considerations, model studies, and a first field case using nine boreholes 500 m apart with depths of 400 m.

New data acquisition and processing techniques (mainly migration before stack) have been developed. The CVA‐seismic method is still in the development stage but promises new possibilities for detailed surveys in difficult areas.