Acoustic Velocity Study in Tight Anhydritic Dolomite of the Late Permian Khuff Formation

Abstract

Carbonate reservoirs are usually associated with diagenesis processes which result in complex mineralogy and pore structure. As a result, rock physics models that predict the petrophsyical properties using seismic based geophysical parameters become more complicated. Most rock physics models studies relate the effect of pore structure and mineralogy to acoustic velocity over a wide range of porosity and mineralogy.

In this study, we are trying to investigate the acoustic velocity response over a narrow range of porosity and mineralogy. Extensive petrophysical and velocity measurements have been conducted on 38 carbonate plug samples. In addition, detailed petrographic and SEM analysis have been done on part of the samples. Results from this investigation highlight the importance of the petrographic analysis to explain the various velocity response. QEMSCAN and FTIR mineralogy quantification techniques provided consistent results over the studied section despite some minor differences. When there is a limited change in pore structure and mineralogy, the carbonate texture and fabric have a major control over velocity.

Biot-Gassmann rock physics model does not provide good estimations in the studied low porosity carbonate rocks. Due to the complicated microstructure, at ultrasonic velocity, these rocks show velocity dispersion effect that leads to underestimated P- and S-wave velocities using the model.