Abstract

Hydrocarbon reservoirs in Mississippian (Kinderhookian to lower Meramecian) rocks in central to southern Kansas and northern Oklahoma include, among other lithologies, limestone and cherty limestone deposited in a basin-margin setting. Cores from 63 wells in this area, together with thin-section petrography and stable C-O isotopic data, provide evidence for the paragenesis of these reservoirs. Replacive chert nodules and layers in muddy slope deposits began to form syndepositionally in the sub-seafloor environment, and they and enclosing sediments were mechanically compacted attending further shallow burial. Relatively minor amounts of dolomite are ubiquitous in the rocks and variously pre-dated, post-dated, and formed concurrently with early silicification. Together, these diagenetic events further reduced rather than created porosity in the rocks. Regardless of specific reservoir age, most porosity in the rocks is dominantly of post-depositional, meteoric dissolution origin related to recurrent episodes of subaerial exposure. Both mesoscale and microscale pores are present, and the dominant types are micro-scale and larger vugs, biomolds, interparticle pores from dissolution of mud matrix, intercrystalline pores in limestone and tripolite, and spicule molds. Porosity is heterogeneously developed in the rocks, and later tectonic fractures, some of which are dissolution-enlarged, enhance permeability in many of the reservoirs. Despite their basin-margin setting, there is only minor evidence of deep-burial diagenesis or the flow of hot fluids through any of the reservoirs.