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.

Keywords: inversion, non-uniqueness, pre-stack, tomography, velocity-depth ambiguity

SINET: Ethiopian Journal of Science Vol. 29(1) 2006: 17–26