Arbuckle Group Platform Strata in Kansas: A Synthesis

Cambrian–Ordovician Arbuckle Group rocks in Kansas occur entirely in the subsurface and are absent only in areas of northeastern and northwestern Kansas and over ancient uplifts and buried Precambrian highs. During Arbuckle deposition, Kansas was located approximately between 20 and 30 south of the equator and south of the Transcontinental arch. Because of the lack of biostratigraphic data and a chronostratigraphic framework, correlation of Arbuckle Group subunits has relied predominantly on lithologic character and insoluble residues. Core studies reveal shallow-water, carbonate-dominated depositional facies that are stacked in vertical cycles (ranging from less than 1 m [3.3 ft] to several meters thick) and cycle sets. Eight depositional facies predominate: (1) clotted algal boundstone (subtidal conditions) with porosities less than 6% and permeabilities less than 0.1 md; (2) muddy to grainy laminated algal boundstones (subtidal to peritidal conditions); muddy textures exhibit porosities generally less than 6% and permeabilities less than 0.1 md, and grainy textures represent some of the best reservoir rock ranging in porosity up to 32% and permeability up to 1500 md; (3) peloidal packstone-grainstone (subtidal to peritidal conditions) with porosities from 0 to 4% and permeabilities generally below 0.005 md; (4) mixed packstone-grainstone (subtidal to peritidal conditions) with porosities from 6 to 18% and permeabilities from 0.1 to 50 md; (5) ooid packstone-grainstone (subtidal to peritidal conditions) with porosities from 11 to 30% and permeabilities from 10 to 1500 md; (6) wackestone-mudstone (restricted subtidal to peritidal conditions) with porosities from 0 to 17% and permeabilities from less than 0.0001 to 1000 md; (7) intra-Arbuckle shale (low-energy subtidal to peritidal and, perhaps, supratidal conditions); and (8) intraclastic conglomerate and breccia, fracture-fill shale, and chert in variable abundances. The abundance of intercrystalline, moldic, fenestral, and vuggy porosity is related to depositional facies, early diagenesis, and dolomitization and not necessarily to karst influence from the upper super-Sauk subaerial exposure surface. Arbuckle reservoirs historically have been viewed as fracture-controlled karstic reservoirs with porosity and permeability influenced by basement structural patterns and subaerial exposure. Although fractures and karst influence production in some Arbuckle reservoirs, the presence of reservoirs where water drive is minimal or absent indicates the dominance of matrix porosity. The Arbuckle in Kansas can be characterized using three end-member reservoir architectures, representing fracture-, karst-, and matrix-dominated architectural systems. Lithofacies and stratal packaging of reservoir and nonreservoir strata exert an important influence in all three reservoir architectures.