NON-DESTRUCTIVE INVESTIGATIONS OF MECHANICAL PROPERTIES AND THERMAL MATURITY IN SOURCE ROCKS

Source rocks are a compositionally diverse lithofacies composed of clay particles, detrital and biogenic minerals, and organic matter comprised of kerogen, bitumen, and pyrobitumen. This assortment of compacted materials composes the fine laminae of the rock structure. The multi-phase and multi-scale nature of these laminae offers an interesting challenge to understand their mechanical properties in relation to the thermal maturity of the organic matter. Traditionally, source rock properties are measured by destructive techniques on bulk samples where the measurements represent composite material properties rather than individual components. For example, mechanical properties are measured by stressing samples to bulk failure, whilst pyrolysis and or solvent extraction are used to determine maturity that result in complete destruction of either the matrix or removal of the soluble organic matter. Thus, these destructive methods do not allow for direct comparison of mechanical properties to the maturity found at the scale of the laminae composing bulk rock samples. However, understanding this relationship is key to determine the potential of a source rock reservoir.

During maturation, burial and exposure to elevated temperatures transforms the kerogen in source rocks. This process causes the breaking of chemical bonds which results in increasing porosity and aromaticity of the kerogen and the generation of bitumen. However, little is understood about how these changes affect the mechanical properties of the kerogen and if this influences bulk rock mechanical moduli. We present a non-destructive, dual-mode examination of source rock maturity and kerogen mechanical properties using Raman Spectroscopy and Atomic Force Microscopy (AFM), respectively. In addition to being non-destructive, these tools provide a unique opportunity to examine kerogen properties at the nano-scale in intact rock samples without extraction. We demonstrate the ability to measure kerogen modulus and thermal maturity of samples that range from Immature to Early Oil, Peak Oil, through to Dry Gas maturity and discuss the challenges associated with such measurements. In addition, we show how variations in both Raman spectra and AFM-measured mechanical properties from intact rock samples may be related to bitumen content.