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Experimentally Quantifying the Impact of Thermal Maturity on Aromaticity and Density in Kerogen
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Kerogen presents challenges when performing well-log-based petrophysical evaluation in organic-rich mudrocks. Two such challenges are the electrical conductivity of thermally matured kerogen and the lack of reliable estimates of kerogen density. Both challenges are due to the effects of the thermal maturation process on the resistivity and density of kerogen embedded in organic-rich mudrocks. Through thermal maturation, kerogen generates hydrocarbons and evolves from hydrogen-rich organic matter into hydrogen-poor residual matter. Alteration in the chemical structure of kerogen leads to increase in kerogen aromaticity, which can be the reason for unexpectedly low electrical resistivity measurements detected in organic-rich rocks. These low resistivity measurements can lead to underestimates in hydrocarbon reserves. Increase in kerogen aromaticity can also cause increase in kerogen density, which can negatively affect the dependability of porosity and water saturation estimated from well logs. To investigate the impact of thermal maturity on aromaticity, resistivity, and density of kerogen, Rock-Eval pyrolysis, solid-state ^13C nuclear magnetic resonance (NMR) spectroscopy, and gas pycnometry were employed. First, kerogen was isolated from organic-rich mudrocks. Select mudrock and isolated kerogen samples were then synthetically matured. Next, aromaticity and electrical resistivity of the mudrock and isolated kerogen samples were evaluated. Lastly, density of the kerogen embedded in the organic-rich mudrocks were estimated. In investigating the chemical, electrical, and physical properties of kerogen, this thesis demonstrated that aromaticity increased, electrical conductivity increased, and density increased in kerogen as a function of thermal maturity. Through natural maturation, as hydrogen index (HI) decreased from 603 to 36 mg hydrocarbon/g organic carbon, aromaticity of kerogen increased from 0.40 to 0.95. In the isolated kerogen samples from Formation A, resistivity decreased four orders of magnitude from 1.32E+7 to 1.18E+3 Ω·m through synthetic maturation from 150°C to 650°C. In organic-rich mudrocks obtained from four formations, quantifications of kerogen density ranged from 1.20 to 1.78 g/cm^3. Results from this research contribute to a better understanding of organic-rich mudrocks and its embedded kerogen as a function of thermal maturity, which can potentially contribute to the development of dependable well-log-based evaluation of in-situ hydrocarbon saturation and porosity in organic-rich mudrocks.
Yang, Anqi (2016). Experimentally Quantifying the Impact of Thermal Maturity on Aromaticity and Density in Kerogen. Master's thesis, Texas A & M University. Available electronically from