Effect of thermal maturity on elastic properties of kerogen

Abstract

We have performed spatially continuous nanodynamic mechanical analysis on four organic-rich shale samples with different thermal maturities to extract the elastic modulus of the kerogen particles. Aliquots were rigorously prepared, and three scans were acquired from each aliquot. Subcritical nitrogen adsorption pore characterization was performed to determine the abundance of kerogen-hosted porosity. To fully characterize the pore system of samples from the oil window, toluene and then chloroform extraction were performed to remove the pore-filling hydrocarbons prior to nitrogen adsorption. The statistical distribution of the measured modulus values was analyzed to extract the properties of the shale particles. In mature samples from the peak oil generation or gas window, the kerogen porosity was the dominant pore morphology. We found that significant lowering of the kerogen particle modulus resulted from intraparticle kerogen porosity. The kerogen particle modulus in mature samples was measured as being lower (7-12 GPa) than the immature sample (15-20 GPa) due to gas-or bitumen-filled pores.

Mesoscale structure, mechanics, and transport properties of source rocks’ organic pore networks

“…1 A ). This decrease of rigidity with thermal maturity is confirmed by experimental indentations (19).…”

“…The presence of hierarchical structures of organic hosted pores evolving through thermal maturation, as probed in scanning electron microscopy (5, 13), small-angle neutron scattering (14–17), and adsorption (3, 14, 18), may affect the overall properties. For example, at an experimental macroscopic scale, the organic porosity has been found to be responsible for a significant reduction of the kerogen particle modulus with respect to thermal maturation (19). In addition, the analysis of gas adsorption isotherms demonstrates that thermal maturity of the organic matter affects the surface area, pore volume, and geometrical permeability (3, 14, 18, 20).…”

Synchrotron tomographic quantification of strain and fracture during simulated thermal maturation of an organic‐rich shale, UK Kimmeridge Clay

“…We hypothesize that these cracks form due to increasing pressure from kerogen decomposition, with differential expansion providing nucleation cites at the interfaces between phases. The fluid pressure in the pore space of kerogen may also influence crack formation [ Zargari et al , ], but was difficult to investigate in our study.…”

The Assessment of Organic Matter Young's Modulus Distribution With Depositional Environment and Maturity

“…Nanoindentation studies on shales with maturity suggest that there is a reduction in effective Young's modulus with increased maturity (Shukla et al, 2013; Zargari et al, 2016) caused by the development of organic intraparticle pores from bitumen generation and migration. If this were to be the case, it would be expected that the proportion of higher modulus values and overall modulus values would decrease with maturity.…”

“…Effective elasticity is affected directly by porosity in studies using both acoustic wave velocity (Allan et al, 2014, 2016; Suwannasri et al, 2018) and nanoindentation, whereby derived organic matter Young's modulus decreases from 20 to 7–12 GPa (Zargari et al, 2016). However, in higher‐resolution studies using AFM, an increase in organic matter Young's modulus is observed with maturity (Emmanuel et al, 2016a; Goodarzi et al, 2017; Li et al, 2018).…”