The Neal(Floyd) Shale of Alabama: Evaluation of Petroleum Generation and Development Potential
Unconventional resource plays across the central and eastern U.S. have significantly increased oil and natural gas production, decreasing the country's dependency on petroleum imports. The Neal Shale, the organic-rich interval of the Floyd Shale in the Black Warrior Basin of northeastern Mississippi and northwestern Alabama, is a potential unconventional petroleum reservoir which ranges in thickness from 25–350 feet. Understanding the controls on reservoir quality and hydraulic fracturing success is critical prior to evaluating the Neal Shale for possible development as a tight oil and/or gas reservoir. A total of 64 samples of well cuttings/core were selected from three wells representing thermal maturity levels ranging from 0.76–1.43% calculated vitrinite reflectance and TOC values ranging from 0.82–4.19% by weight. Characterization of the Neal Shale for mineralogy, inorganic chemical composition, porosity, and brittleness has been performed using various analytical techniques. Reitveld analysis of XRD data correlates well with previously published mineralogic data for the Neal Shale, and allows comparison with XRF compositional data. The XRD and XRF data sets will be correlated with rock strength measurements to obtain a relationship between rock composition and brittleness, to better predict the success of hydraulic fracturing. FIB-SEM-EDS 3D microanalysis of core samples is being conducted to determine the sources of porosity within the shale at different levels of kerogen maturity. Initial 3D microanalytical work shows little kerogen porosity development, indicating that matrix porosity predominates. A kinetic model for porosity development based on TOC, kerogen type, and hydrogen index was used to estimate the porosity resulting from kerogen decomposition to oil and gas. The model will be compared to porosity measurements obtained by FIB-SEM-EDS analysis. The kinetic model is being coupled with a basin model to estimate the type and volume of hydrocarbons that have been generated. Initial basin modeling results indicate that calculated vitrinite reflectance underestimates kerogen maturity and the deeper Neal Shale intervals largely lie within the gas generation window at a 97% transformation ratio of kerogen to hydrocarbons. However, the shallowest interval may have oil generation potential, lying in a late oil formation window, with a 60% kerogen transformation ratio and measured vitrinite reflectance values ranging from 0.9–1.0%.
AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014