Stephanie Vialle
Senior Lecturer
Mechanical and elastic properties of rocks are a complex function of their microstructure and mineralogy. A great number of rock physics models commonly used to estimate fluid saturations and pressures from seismic data rely on a very simplified representation of rock microstructure (cf cement model, inclusion-based models, etc.). These models have been quite successful in the Oil & Gas industry for siliclastic rocks but they are more challenging, if not inappropriate, for rocks with more complex microstructure such as carbonates or shale. Furthermore, the problem becomes even more complicated in case of evolving microstructure and/or mineralogy due to geochemical reactions.
Rock model to link microstructure to reactive flow of CO2
With the Stanford Rock Physics & Borehole Project
I proposed a new approach to link heterogeneities in the rock microstructure (different pore and pore throat sizes) to the movement and chemical reactivity of CO2-rich fluid in carbonates. The key development was to subdivide the rock microstructure into microstructural facies, and express some dimensionless numbers that categorize the different dissolution regimes (i.e. diffusion-, advection-, kinetic-controlled) as a function of the petrophysical properties of each microstructural facies. These numbers are the quantitative link between microstructure and reactive transport.
Quantitative microstructure characterization by nano-indentation and upscaling of elastic properties
With the Dept. of Exploration Geophyiscs, Curtin Uni, Bochum Uni & Stuttgart Uni, Germany
Nano-indentation technique is a method that gives quantitative information by mean of local (micrometer size) measurements of elastic moduli. Developped and well-established for material sciences and homogenous media, there are some challenges to adapt it to heterogenous media such as rocks. Experimental methodology, theory and signal interpretation and processing need to be further developed.
We are working on the experimental methodology at Curtin Uni, with on-site instrument (National Geosequestration Laboratory).
We are testing several ways of upscaling the local measurements of elastic properties to predicy P- and S-wave velocities at a larger scale (laboratory, well-log). In collaroration with Bochum and Stuttgart Unis, we are also implementing the nano-indentation data in a digital rock physics workflow to get better aggreement between computation from digital cores and core-scale lab measurements.
Map (left) and distribution (rigth) of indentation moduli for a microporous carbonate
Vp and Vs trend predictions from Digital Rock Physics. Green are upper HS bonds. From Saenger et al., 2016
Estimation of electrical properties of clean and shaly sand from digital cores
PhD of M. Ali Garba, Curtin Uni
The goal of this work was to establish a robust workflow to digitally compute electrical properties of clean sands and clay/sand mixtures. To do so, formation factor of beach sand samples (clean and mixed in the laboratory with various amounts of clay) was carefully measure in the laboratory over a wide range of porosities obtained by compacting the sand samples; in parallel, formation factor was computed from x-ray microtomography images using the free finite difference code from NIST, and multiple sub-samples of various sizes. We thus compared trends between formation factor and porosity computationally derived with that obtained in the laboratory.
Electrical Formation Factor versus porosity for Scarborough beach sand: comparison between laboratory measurements and computation from digital cores.