USING GEOCHEMICAL DATA TO DETERMINE THE INFLUENCE OF ELEMENTAL CONTENT AND MINERALOGICAL COMPOSITION WITHIN THE CHEROKEE BASIN IN SOUTHEAST KANSAS

Geochemistry is a valuable tool that can be used to analyze unconventional reservoirs such as coal beds that contain natural gas. Several wells located in the Cherokee Basin in Southeast Kansas were analyzed using geochemical and log data. The wells were logged between 224-500 feet and geochemical samples were collected from select depth. The objective of this study was to determine the variations in mineral composition and elemental content in order to describe diagenetic processes and determine the relation between the distribution and presence of specific minerals within the interval. Using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and well log data, the lithofacies composition of the field, with layers above Mississippian units were investigated. Data was obtained from the Kansas Geological Survey and industry partners. Well log data showed that the interval studied is dominantly composed of sandstone and shale with interbedded coal layers, based on our analysis of gamma ray log values and trends. Seven coal beds were identified across the wells with occasional silt beds and carbonates. In the Graham 6-36A-3 well, geochemical results show high amounts of pyrite, specifically within the coal layer at the depth of 425 feet, a shale layer at 435 feet and smaller amounts of pyrite in another shale layer at 467 feet. XRD analysis show that the coal beds also contain significant amounts of Illite, up to 25 weight %. It is noted that where there are high amounts of chlorite, there are low amounts of Kaolinite. For example, at the depth of 442 feet, there is up to 10% Chlorite and no Kaolinite in the layer. Apatite, a phosphate mineral, is also present in significant amounts in some intervals, ranging from 5-20 weight % notably within the shale, limestone and sandstone beds. Preliminary XRF data shows elevated amounts of trace elements such as Mo, V, Ni, and Zn in a coal layer, particularly at the depth of 459 feet. The presence of coal beds and shale layers suggest a low energy swampy environment. Trace elements such as Mo and V indicate euxinic conditions, meaning that the water was sulfuric and anoxic. This study is significant because it provides information about the source and type of coalbed methane, thus improving exploration effort. Knowing the diagenetic processes improves our understanding of paleo depositional conditions.