Petrographic analyses of Middle Pennsylvanian (Desmoinesian) Cherokee Group sandstones in the Mid-Continent show that effective liquid porosities, liquid permeabilities, and pore-size distributions are controlled by sedimentologically influenced petrologic parameters and subsequent diagenetic alterations. Deltaic complexes contain two distinct sandstone-bearing lithologies: (1) subarkosic-quartzarenitic channel sandstones, and (2) sublitharenitic sandstones interstratified with shales representing overbank and interdistributary deposits. The sandstones in these two settings underwent different diagenetic histories, which enhanced original differences in their reservoir properties.

Overbank deposits commonly contain soft, argillaceous rock fragments which underwent plastic deformation during compaction, causing the clogging of some pore-throats and pores. In addition, extensive silica cementation, perhaps due to diagenetic clay mineral conversions, caused further destruction of primary pores. In channel sandstones, porosity reduction was less extensive and apparently proceeded at a slower rate. Chlorite coatings on many grains prevented destruction of original pore spaces by inhibiting further silica cementation. Individual sandstone bodies with abundant coatings fall within a porosity range of 20 to 25%, whereas bodies with uncoated grains rarely exceed 18%. Permeabilities in clay-coated reservoir rocks fall within a 100 to 200 md range, whereas uncoated or spa sely coated rocks are in the 1 to 30 md range. The diagenetic histories of these rocks are further complicated by the development of secondary porosity caused mainly by dissolution of the feldspathic grains and carbonate cements.

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