ILLITE-SMECTITE MIXED LAYER FOR THERMAL MATURITY HISTORY AND POTENTIAL OF THE LATE DEVONIAN-MISSISSIPPIAN WOODFORD SHALE, ARDMORE-ARBUCKLE BASINS, OKLAHOMA

The exploration of unconventional resources, particularly shale gas, to meet North America's energy demand necessitates comprehensive studies of shale rocks from reservoir to microfabric. This study uses clay mineralogy as an insight to the thermal maturity on the late Devonian-Mississippian Woodford Shale in Oklahoma.

The study analyzes twelve outcrop samples from the upper, middle, and lower Woodford at McAlister's Cementary Quarry and Turner falls Oklahoma. Based on the diffraction patterns, illite, kaolinite, I-S mixed layers, quartz, and carbonates were identified as the main clay and non-clay minerals in the clay fractions of these shales. Results show the presence of illite-smectite mixed layers (R≥1) in two samples, indicating a diagenetic origin for the illite. Each diagenetic illite was observed from the lower and middle Woodford. The R≥ 1 stacking order for I-S was consistent with other previously published work (Organic content and Vitrinite reflectance) and suggests that the transformation occurred within a burial temperature range of 100°C-130°C, corresponding to the immature to early oil window of the study area.

These findings will be integrated with other geochemical and paleomagnetic data to deepen understanding of diagenesis and thermal maturity history in the Woodford shale. This comprehensive knowledge will enhance insights into Oklahoma's unconventional shale source rock and aid exploration potential assessments for mid Continent basins. Future work will involve studying clay sample microfabrics using Scanning Electron Microscopy (SEM) to understand further the genesis of the illite clays in relation to other diagenetic features and fabric (pore size).