Pre-Stack Interpretation for Depth Mapping

R. L. Coons

The efficient location and development of oil and gas reserves require the integration of our technical disciplines and close cooperation among geologists, geophysicists and engineers. Yet, we have a problem. The geologist and engineer measure their information in terms of depth below a datum, while the geophysicist is forced to take his measurements in two-way time.

In the early stages of exploration, velocity surveys were rare. We assumed that the relationship between time and depth was relatively simple, changing slowly across the basin. As more data were obtained, particularly when we got two or more velocity surveys in the same field, we found that the time/depth relationships were complex.

What is a stacking velocity? What is the relationship between stacking velocity and RMS or average velocity? How accurately can we determine RMS velocities from stacking velocities? How does a refraction model compare to a model derived from stacking velocities?

An IBM PC-AT with an attached 9-track tape drive has been used to compute stacking velocities, residual statics, and a refraction model from marine data in the presence of 200 m/sec of time distortion caused by near-surface velocity variations. These results illustrate what can be done by an interpreter to improve his understanding of the relationship between time and depth within his prospect area.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.