Porosity interpretation through seismics

Abstract

This paper describes a procedure for porosity interpretation from seismic data (POISE) by exploiting merits of several recent advances in seismic data processing and interpretation.

Briefly, the procedure is as follows: starting from NMO corrected CDP gathers of P-wave data and applying amplitude versus offset (AVO) analysis, one can separate out zero offset “P-wave” and “Swave” stacks both as a function of P-wave time. Here the term “S-wave” refers to a stack that we would have obtained if we had carried out an S-wave survey and displayed the data in P-wave traveltime. Application of maximum likelihood deconvolution/modelling technique on stacks leads to models for P-wave and S-wave reflection coefficients. Finally, inverting the reflection coefficients for interval transit time, a section can be prepared to display ΔT_s-ΔT_p, the difference in slowness of the S-wave and P-wave as a function of the P-wave traveltime.

The final output of POISE for ΔT_s-ΔT_p is particularly useful for studying variations in lithology and porosity within a formation. The interpretation is fouSnded on an empirical observation by Ikwuakor that ΔT_s-ΔT_p from character logs for a large number of carbonate and sandstone samples, is proportional to the core porosity (for a given rock type).

The utility of POISE is illustrated with a field example in a carbonate reservoir.