Resolution, Bandwidth, and Money: ABSTRACT

Abstract

Our preoccupation with big structure is over. Today the geophysicist and geologist, together, must establish small-scale stratigraphy and faulting, delineate the limits of reservoirs, and compute rock properties. Critical to these efforts is resolution-the End_Page 890------------------------------ ability to see small features. Resolution, both vertical and horizontal, depends on the seismic bandwidth. Obviously, this requires high frequencies. There is also value in the low frequencies, particularly to the geologist using pseudo-logs or searching for gradual transitions of rock properties. First steps to improve the bandwidth involve deconvolution in association with good field technique, good field discipline, and additional processing. These improvements are inexpensive, but limited. Thereafter, we depend on improvements in the source; these improvements begin to increase the cost significantly. In explosive work, improvements can be made by manipulating the charge size, the depth, and the ghost reflection; many small charges and a few large charges may be combined in the CDP technique. The Vibroseis system does more; it allows us to precompensate the seismic signal for any expected attentuation. In principle, we can raise any frequency above the noise merely by transmitting it for a longer time. However, desirable increases of bandwidth can increase the cost of the field work by several times. There is no limit to the bandwidth we can achieve, but bandwidth is expensive. Delineation wells (and certainly dry holes) are even more expensive. We must find a new balance of cost-effectiveness. End_of_Article - Last_Page 891------------