Study of the Mechanical Behavior of Organic Matters Contained in Source Rocks: New Insights into the Role of Bitumen

Abstract

Assessment of mechanical properties of organic matters contained in unconventional formations is needed to understand the geomechanics of source rocks. The organic matters are part of the source rock matrix, and they are made of kerogen and bitumen. Although the literature has some studies addressing the properties of kerogen and bitumen, no apparent attempts were made to address the mechanical behavior of organic matters as a combination of both. Isolation of organic matters from the rocks for experimental assessments has some risks of altering the original properties because of their delicate nature and their existence as micro- and nanoconstituents. Some computational approaches such as molecular simulation can serve as an alternative platform for the purpose of delineating organic matter properties including the mechanical ones. This work implements available 3D molecular modeling of kerogen and bitumen with different ratios to mimic organic matters that can be investigated for the mechanical properties. Upon the recreation of different configurations of organic matters molecularly, mechanical parameters such Young’s, bulk, and shear constants, as well as the stress–strain relationship for the elastic and plastic deformations were extracted. The mechanical behavior was closely monitored before and after saturation with a number of gases that are commonly found in subsurface formations such as methane, carbon dioxide, and nitrogen. The results revealed that the organic matters had a mechanical behavior envelope similar to what were reported for organic-based materials such as polymers. Moreover, the structures containing bitumen exhibited larger values of Poisson’s ratio, indicating less likelihood of them to degrade upon applied stresses. The presented data substantiate the importance of accounting for both bitumen and kerogen in modeling the petrophysics and the mechanical behavior of the organic matters.

Adsorption–Desorption Hysteresis in Shale Formation: New Insights into the Underlying Mechanisms

“…For a cubic cell, the total number of elements was reduced to three. Variation in the strain matrix can be followed to calculate bulk, Young’s, and shear moduli . The selected values of strain were within the elastic region as suggested in some other similar studies (i.e., 0.025 and 0.05). , The calculated bulk modulus of the kerogen types adopted in this study along with some experimental measurements of other kerogen samples from the Green River basin is given in Table .…”