Common Transmission Point (CTP) Gathers: A New Domain for Amplitude Variation with Offset

Abstract

Analysis of amplitudes of transmitted waves (TAVO) is an extension of the conventional AVO analysis using amplitudes of reflected waves. In this study, we introduce the common transmission point (CTP) gather, which is a new domain that is convenient for TAVO analysis. A CTP gather is formed by binning traces that have the same transmission point across a layer interface. We use the proposed domain to invert the ratios Δαα, Δρρ, Δββ, and βα in a model consisting of a gas channel nestled within an oil reservoir. The TAVO equations are fitted to amplitudes calculated by Zoeppritz equations within CTPs inside and outside the channel. Within each CTP gather, we use all traces with incidence angles less than 90% of the critical angle (if any) as TAVO approximations break down beyond this point. The proposed CTP TAVO analysis method estimated Δαα, Δρρ, Δββ, and βα in the gas channel within 1% of their corresponding true values.

Keywords

• converted waves
• VSP survey
• reservoir parameter estimation
• amplitude variation with offset