Impact of seismic source/receiver directivity on sub-basalt imaging

Abstract

Many sedimentary basins considered for hydrocarbon exploration are overlaid by basalt layers which disrupts seismic wave propagation due to its properties.

A single large gun has a nearly spherical directivity and at low frequencies a regular array still generates a significant portion of energy beyond the critical angle to the top basalt interface, I propose the use of long arrays to limit the directivity into a sub critical angle range. Finite difference modelling was performed in order to determine the applicability of long arrays to acquisition considering how extreme directivity patterns affect the source signature and hence the deconvolution process, it was found that a 120m long array has an almost identical time pressure wave let up to 30º-35º in the inline plane for a frequency band of 5-25Hz. Using simple analytical models it becomes evident that long source arrays are more efficient than single sources and regular arrays,into focusing energy to travel vertically down.