Abstract

Porosity data are derived from borehole-gravity measurements and from suites of acoustic, neutron, and density logs. Carbonate porosity was affected by a variety of diagenetic processes. Curves of porosity versus depth, reflecting large-scale porosity-loss processes in the subsurface, are derived for a composite carbonate section and for carbonate strata of different ages and compositions. The decrease of porosity with depth can be characterized by the exponential function phi = 41.73e (super -z/8197) (ft) [phi = 41.73e (super -z/2498) (m)], where phi is the porosity (%) and z is the depth below ground level. Average porosity is reduced by a factor of two in a depth interval of about 5,700 ft. Carbonate strata of different ages that are buried to equal depths show no systematic porosity differences. Dolomite porosity is lower than limestone porosity in the near surface, but does not decrease as rapidly with depth. Dolomitization occurred early and either reduced original porosity or selectively favored lower-porosity limestones. With continued burial, dolomite was more resistant than limestone to associated porosity-reducing effects.--Modified journal abstract.

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