Studying the mechanical properties of geological rock samples at micro- and nano- scales with atomic force microscopy-based techniques

Yu.S. Zamula¹, E.S. Batyrshin¹, S.S. Chugunov²

¹Center for micro- and nanoscale dynamics of dispersed systems, Bashkir State University, Ufa, Russia

²Skoltech Center for Hydrocarbon Recovery, Skolkovo Institute of Science and Technology, Skolkovo, Moscow Region, Russia

6cef79f97a1348byuriyzamula@gmail.com

Studying mechanical properties of rock is an important part of a geomechanical characterization workflow applied to geological formations, containing recoverable hydrocarbon resources, consumable water, or holding CO₂ or nuclear waste. Traditional mechanical tests are mostly focused on studying centimeter-sized rock samples with provision of integral mechanical characteristics of rock. Application of Atomic Force Microscopy (AFM) to mechanical studies of geological materials allows resolving integral mechanical characteristics down to properties of individual grains and intergranular interfaces. AFM technology helps to acquire a deep insight into internal structure of rock, to understand rock mechanics at micro-scale, and to forecast rock behavior under different stimulation regimes, with the help of additional numerical modeling.

Geological rock samples are composite materials often consisting of a large number of mineral and organic phases. Due to natural anisotropy of certain rocks, the values of their mechanical properties experience a broad variation within mineral and organic phases. This variation is typically observed at micro- and nano-scale; these effects effects can be successfully captured with an AFM technique. Comprehensive AFM analysis of rock samples includes mapping of effective elastic modulus of mineral and organic phases over the sample area, studying anisotropy of mechanical properties within particular grains and characterization of intergranular interfaces.

In this work, the effective elastic modulus of rock samples from a West Siberian unconventional oil field were mapped at micrometer resolution using two AFM nanoindentation techniques: (1) building "force-distance" curves in nanoindentation mode of AFM and (2) operation of AFM probe in oscillating intermittent contact mode. The obtained results were compared to the data acquired with a dedicated nanoindenter device from the same rock samples.

This research is supported by the Grants of the Ministry of Education and Science of the Russian Federation (11.G34.31.0040) and Skoltech Partnership Program.