UNIQUE DETERMINATION OF STRUCTURE AND VELOCITY BY 3-D TOMOGRAPHIC INVERSION OF REFLECTED AND REFRACTED WAVES

Abstract

Accurate determinations of interface depths and velocity fields are crucial for the oil
industries in their search for hydrocarbon reservoirs. However, the so called velocity-depth ambiguity
has always been a problem with the seismic reflection data that is normally used in petroleum
exploration. In this paper the cause of this velocity-depth ambiguity is examined and a methodology is
proposed that minimizes non-uniqueness in the inversion results. It is shown that simultaneous
inversion of zero offset and offset reflection data as well as refraction data can reproduce accurate
velocity-depth model using only certain picked seismic events. A subsequent 2-D Prestack depth
migration based on the Kirchhoff method utilizing the velocity field obtained from the tomographic
inversion extracts more information from the data and gives a clear picture of the subsurface. The
superiority of the simultaneous inversion of the reflected and refracted waves to that of reflected waves
alone is demonstrated using real data