GEOCHEMICAL AND PETROPHYSICAL CHARACTERISTICS OF THE NEW ALBANY SHALE IN INDIANA AND ILLINOIS

The upper Devonian New Albany Shale has become one of the most promising targets for hydrocarbon exploration in the Illinois Basin. The average thickness of the New Albany Shale is 100-140 ft and towards the southwest part of the Illinois Basin the thickness reaches up to 460 ft near the intersection of Kentucky, Illinois and Indiana. Geochemical and petrophysical properties of the organic-rich source rocks are key in predicting their hydrocarbons potential. This research utilized 40 rock samples of two drilled wells from the Illinois and Indiana Basin. Here total organic carbon (TOC) content, Rock-Eval pyrolysis and X-ray diffraction (XRD) analysis were performed on the studied samples to decipher the abundance of organic matter, organic matter type, thermal maturation level via vitrinite reflectance and quantitative mineral composition of the New Albany Shale. TOC contents of the New Albany Shale range from 0.04-8.59 wt.%, with an average of 4.57 wt.%. Moderate hydrogen index values have been noticed in the studied specimens, with a mean value of 350 mg HC/g TOC. Van Krevelen diagram using pyrolysis oxygen index (OI) and hydrogen index (HI) exhibit the existence of mixed type II/III kerogen with the potential to produce oil/gas. The vacuum saturation technique was utilized to obtain the porosity, bulk density, and grain density. Additionally, the mercury intrusion porosimetry (MIP) and small-angle X-ray scattering (SAXS) techniques were used to understand better the surface features (especially pore characterization) at nm-µm scales. Mineral composition using XRD shows high values of quartz, feldspars and clay minerals (illite and kaolinite). The size of the pore throat diameters from MIP analyses mostly ranges from 2.8-50 nm zones, along with an average porosity of 5%. The SAXS results show the average pore size diameter of 1-5 nm in Illinois and Indiana samples. For the more comprehensive unconventional potential, paleoenvironmental conditions and pore characterization, more techniques will be adopted, such as GC-MS, x-ray fluorescence, field emission-scanning electron microscopy-SEM, thin-section studies (maceral identification), and nuclear magnetic resonance (NMR).

Keywords: Total organic carbon, X-ray diffraction, Rock-Eval pyrolysis, thermal maturation, mercury injection