Hydrocarbon Reservoir Exploration Strategies Applied to Paleozoic Calcite Sea: Example from Mississippian Chester "J" Limestone, Southwest Trivoli Field, Oklahoma
Carolyn G. Roshong, John D. Pigott
Secular tectonically linked changes in Phanerozoic ocean-atmospheric CO2 affect the primary mineralogy of marine carbonate precipitates (e.g., times of high PCO2 are times of widespread low-Mg calcites, and times of low PCO2 are generally times of high-Mg calcite-aragonites). Owing to differences in diagenetic susceptibilities, hydrocarbon reservoir exploration strategies in "calcite seas" are different from those applied to "aragonite seas." Our example of the former is derived from a detailed subsurface study of the late Mississippian Chester "J" limestone, Southwest Trivoli field, Dewey and Major Counties, Oklahoma. The open marine shelf carbonate buildup is documented by a vertical regressive sequence of lithofaci s. Toward the top of the Chester "J," terrigenous quartz increases with a gamma-ray distinctive shale marking the Mississippian-Pennsylvanian unconformity.
Interparticle and secondary vuggy porosity are the dominant porosity types with lithofacies-dependent permeability-porosity correlations. Suggested diagenetic controls upon porosity are the presence of lime mud and the amount of bryozoan versus crinoid skeletal allochems. The former prevents extensive sparry calcite cementation,the latter affects the amount of early syntaxial cement. Rim cemented barriers and impermeable bedding planes control the formation of localized porosity and permeability zones, one diagenetic hydrocarbon trapping mechanism.
The five major distinguishable diagenetic environments are (1) marine phreatic, (2) mixing zone, (3) meteoric phreatic, (4) meteoric vadose, and (5) complex shallow to deep subsurface. Diagenetic overprinting is ubiquitous.
Changes in acoustic impedance as a function of porosity in Southwest Trivoli field can be forward seismic modeled. The models demonstrate the potential applicability of geophysical mapping on existing seismic lines of diagenetic porosity in these carbonates.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.