NON-DESTRUCTIVE INVESTIGATIONS OF THE THERMAL MATURITY AND MECHANICAL PROPERTIES OF SOURCE ROCKS
S. L. Eichmann1,▲, D. Jacobi2*, M. H. Haque1,▲ and N. A. Burnham3
1 Aramco Services Company, Aramco Research Center: Boston, Cambridge, Massachusetts 02139, USA.
2 Aramco Services Company, Aramco Research Center: Houston, Houston, Texas 77084, USA.
3 Physics and Biomedical Engineering Departments, Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts 01609, USA.
▲ Current address: Aramco Services Company: Aramco Research Center: Houston, Houston, Texas 77084, USA.
* Corresponding author, email: David.Jacobi@Aramcoservices.com
Source rocks consist of diverse lithofacies whose composition can vary according to the depositional environment and the provenance of the sediment composing the rock matrix. In general, the rock fabric is made up of very fine grained, laminated and non-laminated intervals composed of authigenic, detrital and biogenic minerals, together with organic matter consisting of kerogen, bitumen and pyrobitumen. During burial, exposure to elevated temperatures and pressures transforms the kerogen in a source rock into hydrocarbons. This transformation is tracked according to different stages of maturity, and results in increases in both the porosity and aromaticity of the kerogen within the rock and the formation of pyrobitumen. Little is understood about how these changes affect the mechanical properties of the organic matter contained in the rock, or to what degree this also influences bulk rock mechanical moduli. Understanding this relationship is essential to determine the production potential of a “source rock reservoir”, i.e. an unconventional self-sourced reservoir from which oil and gas can be recovered through hydraulic fracturing of the rock matrix. Direct measurement of the mechanical properties of organic matter in relation to its thermogenic transformation, however, is a challenge due to the small size of the materials composing the rock fabric, especially with source rocks that are finely laminated. To explore this relationship, the results of a non-destructive, dual-mode examination of source rock maturity and kerogen mechanical properties is presented using Raman spectroscopy and Atomic Force Microscopy (AFM), respectively. The analysed samples (n = 5) are a Silurian source rock from the Middle East. The results demonstrate the ability to measure both mechanical moduli and thermal maturity of organic components in intact source rock samples which range in maturity from the catagenesis through the metagenesis stages i.e %Ro from 0.6 to 1.6. These techniques provide an opportunity to examine kerogen, bitumen and pyrobitumen properties at the micro- and nano-scale using intact rock samples without disruption of the rock fabric, which readily occurs with conventional bulk core analysis techniques.
Key words: source rocks, mechanical moduli, thermal maturation, kerogen, Raman spectroscopy, atomic force microscopy.
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