PETROPHYSICAL CHARACTERIZATION OF THE CONTACT BETWEEN THE FORT PAYNE FORMATION AND THE CHATTANOOGA SHALE

To date, more than 3,000 oil and gas wells have targeted Mississippian rocks in the Upper Cumberland region of Tennessee and Kentucky. The plays are primarily stratigraphic, resulting from porosity and permeability variations in thick sequences of carbonate and clastic rocks. One challenge has been the down-hole identification of sedimentary geometries such as submarine channels or carbonate mounds that likely control the size and shape of hydrocarbon reservoirs in the region. Understanding these features is key for continued exploration; thus, the purpose of this study is to use a hand-held gamma ray scintillometer to characterize sedimentary bodies at the contact between the Chattanooga Shale (Devonian) and the overlying Mississippian sequence in south-central Kentucky.

The research area includes two outcrops near Burkesville, Kentucky on KY Highway 61. The first outcrop is a three meter thick sequence of Chattanooga Shale that contains pyrite nodules and exhibits minimal weathering and oxidation (36°53’26.46”N and 85°25’24.53”W). The second study area, less than a quarter mile away, is an outcrop of the Fort Payne Formation that measures approximately 15 meters thick (36°54’2.44”N and 85°25’48.32”W). Facies observed in the Fort Payne are interbedded carbonate and siliciclastic mudstones as well as crinoidal packstones and grainstones.

Scintillometer measurements were taken every 20 cm from the base to the top of both outcrops. In addition to a general measurement of gamma radiation dose rate, the Gamma Surveyor II was used to measure potassium (%), uranium (ppm), and thorium (ppm). Preliminary results indicate that: (1) the mean dose rate of the Chattanooga Shale is nearly 18 times greater than dose rates measured in the Fort Payne; and (2) abundances of potassium, uranium, and thorium are orders of magnitude higher in the organic-rich siliciclastic Chattanooga Shale compared to mixed siliciclastic and carbonate shales of the Fort Payne Formation. Future work will focus on interpreting sedimentary geometries in the study area and comparing scintillometer results to nearby wireline logs from the same stratigraphic interval.