Sequence Stratigraphy and Micro-Image Analysis of the Upper Morrow Sandstone in the Mustang East Field, Morton County, Kansas

Abstract

The early Pennsylvanian upper Morrow sandstone was studied in the Mustang East field of Morton County, Kansas. A rich data set including wireline logs, whole core, and micro-resistivity images were available for interpretation. Data from core, thin section, X-ray diffraction, scanning electron microscopy, cross sections and subsurface isopach maps were integrated to interpret the depositional and diagenetic processes that influence genesis of the Morrow sandstone reservoirs. The upper Morrow sandstones are stratigraphicaly located below the Atokan Thirteen Finger Limestone and above the “Squaw Belly” or middle Morrow. These sandstones represent deposition by fluvial to estuarine processes and are completely encased in marine mudrocks. The upper Morrow sandstone deposits within the study area resulted from stream incisement into the low relief Hugoton Embayment/Anadarko Shelf. Subsequent flooding of these valleys trapped siliciclastic material within the valleys forming heterogeneous complexes. Core-calibrated micro-image analysis indicates that deposition within the system is characterized by fining-upward, pebble-conglomerate to coarse-grained fluvial sandstones that are overlain by estuarine and marine deposits. The pebble conglomerates are in erosive (unconformable) contact with the underlying marine mudstones. The upper Morrow incised valleys appear to be underfed and sediment starved. The pebble conglomerate to coarse-grained sandstone’s of the upper Morrow interval provide excellent reservoirs for oil and gas. The complete encasement of these sandstones within marine mudrocks make them lucrative, but elusive, drilling targets within the Hugoton Embayment.