Micromechanics and shear strength of fractured shales

Frictional properties of fractures in shale are of great importance for many engineering applications. Stability of fractured shales plays a major role in hydrocarbon production, CO2 storage and constructions in shaly formations. Properties of such fractures can both be measured in the laboratory and determined through modelling. There are several analytical, simple models that can be used to estimate the strength properties of fractures, some of them may fit better for shale.

Several shale samples have been tested at the Norwegian Geotechnical Institute (NGI). The successful candidate will compile the results of the tests and use different analytical models/equations to estimate the peak and residual friction coefficient of shale samples (Fig. below). Then, the candidate will link the results to micromechanics of fractures surface and conclude on the model(s) that fit better for shale.

The candidate may also use photogrammetry or other techniques for characterizing fracture surface and link properties of fracture surfaces to the mechanical strength of the samples.

Objective:

The objective of this study is to investigate and estimate/model strength and friction properties of fractures in shale using analytical solutions.

Material:

The candidate may need material for additional characterization or testing. There is already core material available at NGI laboratory that can be used for this study.

Research method:

The work includes:

  • Evaluation of the data on shale characterization and testing available at NGI
  • Review of the existing models for estimating frictional properties of fractures
  • Simulating friction of shale samples and proposing the best models applicable to shale samples tested.

Learning outcomes and industry relevance:

The candidate will get familiar with the characterization methods for shales and mechanical testing equipment at NGI laboratory.

After completing this work the candidate will also have the proficiency to characterize shales using geological and rock mechanical methods and work with research projects funded by the Research Council of Norway, Equinor, and Total.

The study is strongly linked to the CO2 storage studies in the North Sea as well as tunnelling and construction in rocks.

Friction coefficient of a shale sample versus shear displacement, measured in the laboratory and estimated through Barton-Bandis (BB) analytical model. Source: NGI.

 

Published Oct. 14, 2019 12:26 PM - Last modified Oct. 14, 2019 12:26 PM

Scope (credits)

60