Advertisement

Shale Capillarity, Osmotic Suction and Permeability, and Solutions to Practical Testing Issues

  • Russell T. EwyEmail author
Conference paper
Part of the Springer Series in Geomechanics and Geoengineering book series (SSGG)

Abstract

For typical shales (void ratio 0.15 to 0.42), modal pore throat sizes range from a few nm to a few tens of nm. Unstressed shales, even when fully saturated, have negative pore water pressure (capillary tension). However, the total suction is often greater than this, especially for highly-compacted shales with extremely small pore size. The additional suction is due to effects associated with clay surfaces. Osmotic pressures can be directly measured, and they can easily be several MPa, a combination of solute suction and clay-related effects. The small pore sizes in shales also result in extremely low values of permeability and of consolidation coefficient. All these characteristics directly impact testing protocols. The first step in any test should be to apply sufficient confining stress to raise the pore pressure up to a positive, measured value. Undrained consolidation, combined with undrained triaxial compression and with small sample sizes (and drainage screens when necessary), results in acceptable test durations. A range of effective consolidation stress values is attained by first equilibrating shale samples in varying amounts of suction, to vary the water content. Non-aqueous fluids are required when sampling, to avoid swelling, and are often necessary for pore lines if osmotic pressures are to be avoided.

Keywords

Pore Water Pore Pressure Osmotic Pressure Void Ratio Triaxial Compression 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References

  1. Ewy RT, Stankovich RJ (2000) Pore pressure change due to shale-fluid interactions: Measurements under simulated wellbore conditions. In: Pacific Rocks 2000, 4th North American rock mechanical symposium, Seattle, USA, 31 July–3 August. Balkema, Rotterdam, pp 147–154 Google Scholar
  2. Ewy RT, Stankovic RJ (2010) Shale swelling, osmosis, and acoustic changes measured under simulated downhole conditions. SPE Drilling & Completion, SPE 78160, pp 177–186, JuneGoogle Scholar
  3. Ewy RT (2014) Shale swelling/shrinkage and water content change due to imposed suction and due to direct brine contact. Acta Geotech 9:869–886CrossRefGoogle Scholar
  4. Ewy RT (2015) Shale/claystone response to air and liquid exposure, and implications for handling, sampling and testing. Int J Rock Mech Min Sci 80:388–401Google Scholar
  5. Head KH (1998) Manual of soil laboratory testing: Effective stress tests, vol 3. Wiley, ChichesterGoogle Scholar
  6. Steiger RP, Leung PK (1991) Consolidated undrained triaxial test procedure for shales. In: Proceedings of 32nd U.S. rock mechanical symposium, Norman, OK, USA, pp 637–646. Balkema, RotterdamGoogle Scholar

Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Chevron Energy Technology Co.San RamonUSA

Personalised recommendations