The relationship between acoustic properties and the petrographic character of carbonate rocks

Abstract

Laboratory studies of the detailed relationships between acoustic properties and the petrographic character of brine‐ and air‐saturated carbonate rocks with a wide range of facies, porosities, lithologies, and rock fabrics indicate that porosity is the major factor influencing both P- and S-wave impedance and velocity. Primary lithology and secondary mineralogy have only a small influence on impedance and velocity. Combined use of P- and S-wave velocity data discriminates porosity changes from lithologic changes. All other variables, including pore‐fluid type and petrographic fabric, have no significant influence on velocities. Laboratory measurements of P‐wave velocity under simulated in‐situ conditions reproduce well‐log velocity values reliably. Laboratory porosity‐velocity trends agree with the time‐average equation when the correct matrix velocities are used. Rock property results were used to interpret porosity/lithology variations for an inverted seismic section from the Williston basin. Where well control was available, the porosity/lithology interpretation was found to be in agreement with the subsurface control.