Combining field description, in situ minipermeameter measurements, geostatistical analysis, and ground penetrating radar (GPR) analysis permits development of an interwell-scale 3D characterization of sandstone deposits. In the Tonganoxie Sandstone incised-valley-fill (IVF) system in the Pennsylvanian of eastern Kansas, outcrop analogs were examined in order to determine the types of macroforms that exist in the system, describe architectural elements and their orientation, and provide estimates of the variations in permeability values in these elements. In the Tonganoxie Sandstone, fluvial and fluvially-influenced, estuarine (FIE) sandstones are present that are potential reservoir analogs for numerous IVF oil and gas reservoirs in the Pennsylvanian of the midcontinent. Two outcrop sites were studied, one of fluvial sandstone and the other of FIE sandstone. The sites were analyzed in terms of their flow unit characteristics by combining geological descriptions utilizing architectural element analysis with geostatistical descriptions of their permeability structure. Conventional statistical analyses and semivariograms were used to determine the permeability structures and the horizontal continuity of permeability values within flow units identified at the sites. The results of the analysis of permeability measurements taken along the two exposures are discussed and the sites are compared in order to highlight differences in their permeability structures. In addition, the fluvial study site was investigated using a combination of information from outcrop description and three-dimensional GPR analysis. A grid of high-resolution GPR profiles showed the three-dimensional (3D) geometry of component elements in one of the flow units identified at the fluvial site and was used to establish the size, spatial continuity, and general transport directions for several of these elements. This study provides geological descriptions, geometric information, and geostatistical descriptions of macroform types that are thought to commonly occur in subsurface IVF reservoirs.

Abstract The Cherokee basin in southeastern Kansas is a shallow, cratonic downwarp adjacent to the Arkoma basin to the south and the Ozark uplift to the east. Nearby pre-Pennsylvanian carbonates of the Ozarks host several MVT lead-zinc deposits that provide evidence of late Paleozoic basinal fluid invasion. These carbonates constitute a prominent regional aquifer which extends into the Cherokee basin, where it is confined by Pennsylvanian-Permian mud-rich clastics and carbonates. The late-diagenetic assemblage in Pennsylvanian sandstones and limestones is characterized by a widespread dissolution event, baroque ankerite or Fe-dolomite, Ba-Sr sulfates and kaolinite. Such an assemblage normally forms under 3 to 4 km of burial, but the investigated strata have never been buried more than 1.8 km. This anomalous late diagenesis is interpreted to have been caused by regional fluid invasion and related advective heating which advanced the zone of extensive diagenesis towards the depths where alterations of the described type are not expected to be found. Fluid inclusion studies indicate that the succession of latediagenetic fluids includes an earlier Na-Ca-brine with salinities up to 25 wt.% NaCl eq. and temperatures of 80-85°C or higher, followed by a later Na-rich brine with salinities of about 19-21 wt.% NaCl eq. and temperatures up to 150°C. Paragenetic trends defined by Ca-Mg-Fe, Mn, Sr, and stable isotopic composition of late-diagenetic carbonate cements indicate early replacement of preexisting carbonates followed by dissolution of framework grains and earlier replacive phases and precipitation of several generations of baroque carbonates. The overall progression from a more rock-dominated to a more waterdominated system corresponds to the identified succession of late-diagenetic fluids and may reflect the regional evolution of the flow system. Compositional differences between cements in sandstones and limestones reflect local lithologic control. Late carbonate cements in limestones utilized local sources of Mg and Ca, whereas cements in sandstones utilized local sources of Fe, Mn and 12 C-enriched bicarbonate. The original chemistry of the incoming fluids was strongly modified by water/rock interaction with local components, therefore separation of local and regional signatures is a key,step in unraveling the evolution of basin-wide flow systems.