Near-surface sand effects

The Rub' Al-Khali desert, located in the southeastern corner of Saudi Arabia, is an area of gravel plains and salt flats overlain by mountainous sand dunes that are typically 90 m high and commonly reach heights of 180 m. Aramco has conducted various exploration activities in this area for several decades. Hoke (1967) describes some of the early refraction work. Robinson and Al-Husseini (1982) detail the field methodology for modern seismic reflection prospecting. Because of the regular nature of the desert floor, near-surface statics are minimal except in the presence of sand, where one-way static corrections can exceed 100 ms and where seismic continuity, which is usually excellent, decreases markedly. The problem faced by data processing has always been one of improving the stack response underneath sand dunes. It was originally thought that poor coupling and unresolved statics were the primary contributors to degradation. The treatment of statics has received considerable attention and it can now be shown that the loss of stack response is not due to incorrect statics. This article demonstrates that, contrary to previous thoughts, the level of seismic energy actually increases dramatically within sand dunes; but that this energy is trapped by the dune, severely reducing penetration into the subsurface underneath the sand. This observation leads to the design of a frequency-wavenumber (F-K) domain filter which provides a degree of signal enhancement to the field records.