NEW AND FUTURE DEVELOPMENTS IN SEISMIC EXPLORATION

Abstract

Present research in reflection seismic prospecting is proceeding with three major goals.

Intensive work is being done on the problem of obtaining useful reflections beneath complex near-surface materials. Such near-surface materials distort both the down-going and reflected wavefronts to an extent that deep reflections either cannot be distinguished or are so distorted as to conceal their true shapes. Current research seeks methods for obtaining enough information about near-surface irregularities to construct a model upon which to base a wavefront correction.

The second major goal is to improve the resolution of the seismic reflection process. Resolution is lost because high frequencies are often weak in seismic sources and are severely attenuated by the earth, by receiver arrays, and by most processing steps. Seismic bandwidth can be increased by improving the high frequency output of the seismic source to compensate for attentuation in the earth, by reducing the size of receiver arrays, and by drastically reducing the inaccuracies of conventional processing algorithms.

The third line of investigation seeks to increase the amount of information extracted from the seismic signal. The first step in this direction was the bright-spot technique, in which qualitative information on seismic reflection amplitudes was used to identify hydrocarbon deposits. Interval velocity estimation was a natural result of moving from a qualitative to a quantitative analysis of amplitudes. In theory, with a combination of P and S wave reflection data, virtually all elastic properties of subsurface rocks could be extracted from the data.

In the more distant future, computers could handle complex interpretation tasks and make drilling decisions.

The principal barrier to rapid implementation of virtually all of the new techniques is inadequate computer power. Despite the explosive growth of the power of computers, mainframe manufacturers have been unable to satisfy the even more rapidly increasing demands of geophysicists. Innovative processing techniques and specialized computer equipment will be essential to continuing rapid progress in geophysical exploration.