Carbonate porosity from S/P traveltime ratios

Abstract

A twenty‐mile S‐wave seismic line was acquired on the northeastern shelf of the Anadarko basin by the 1977–1978 Conoco P‐Wave/S‐Wave Group Shoot. The resolution of the S‐wave section is at least as good as the resolution of a coincident P‐wave section acquired in 1975. The top and bottom of a collection of Paleozoic carbonates called the Hunton group can be identified on both sets of data. P and S traveltimes and traveltime ratios delineate lateral variations in the thickness and average porosity of the Hunton. Where the pore space is saturated with liquid, a systematic increase in average porosity from less than 2 percent to about 11 percent correlates with an increase in the S/P traveltime ratio from 1.84 to 1.96. The ratio decreases to values between 1.65 and 1.80 at two places along the line, probably indicating that the pore space is partially gas‐saturated at these locations. The data are consistent with the seismic response of a petrophysical model of the Hunton in which a majority of the pore shapes are elongated rather than round.