Impact of Diagenetic Overprints on Reservoir Quality and Heterogeneity, Upper Morrow Sandstone, Morton County, Kansas

Abstract

Integrated analysis of three cores along with well logs yielded eight distinct lithofacies associated with fluvial, estuarine and marine environments of deposition. The marine facies M-1 and M-2, which are fossiliferous shale and sandstone, are not reservoirs. The better reservoirs are F-2 facies which consists of coarse-grained sandstone to granule conglomerate with average porosity of 20.4% and permeability of 35.2md. F-2 sandstone represents braided stream deposits. Other fluvial facies are F-1 channel lag conglomerate, F-3 meandering stream sandstone and F-4 abandoned channel fill shale, siltstone and coal. F-1 facies are poor reservoirs due to carbonate cement and pseudomatrix. Average porosity in the F-1 facies is 7.3% and permeability is 2.3md. F-3 represent reservoirs and have average porosity of 15.4% and permeability of 17md. F-4 facies is generally low porosity and permeability due to the presence of silty and clay matrix. The average porosity for F-4 facies is 6-6% and permeability is 0.63md. Estuarine facies E-1 and E-2 have highly variable reservoir properties that depend on the amount of clayey material and burrowing that destroyed the original bedding. F-4, E-1 and E-2 facies tend to form flow barrier that contribute to reservoir heterogeneity. Mapping individual facies is critical to determine the distribution of reservoir (flow units) and sealing facies in the upper Morrow sandstone.</