Gas Migration in Shear Zones (GAM) - Laboratory Studies

The laboratory tests were focused on three main issues.


  1. Development of new coring techniques to recover undisturbed shear zone samples
     
  2. Porosity and permeability measurements
     
  3. Visualisation and structural analysis of pore spaces in a shear zone sample

Development of new coring techniques to recover undisturbed shear zone samples. (Sandia Labs)

Innovative coring techniques have been implemented both in the field and in the laboratory to minimise damage to the shear zone. These techniques were used to obtain porosity, permeability, and pore visualisation specimens from matrix and shear zone materials.

GAM : Coring technique
GAM : Coring technique with resin

GAM : Porosities graph Porosities are shown as a function of effective confining pressure for Core #1. This core sample includes both shear zone and matrix material. Porosity is less than 1% and decreases with increasing effective confinement
GAM : Permeabilities graph Gas permeabilities were obtained at a constant effective confining pressure (2.1 MPa for these data), but at different combinations of pore and absolute confining pressures. The permeabilities are plotted as a function of reciprocal pressure to obtain Klinkenberg-corrected permeabilities.
GAM : Relative Permeabilities graph Relative permeabilities were measured in September and December of 1998. The water permeability curves are essentially continuous for the two measurements; however the gas (N2) permeabilities are not. As water saturation increases the gas permeability drops. Intrinsic liquid permeabilities measured at 100% saturation are also shown.
GAM : Capillary Pressure graph Capillary pressure measurements begin with a liquid-saturated specimen. Gas (nitrogen) pressure is incremented in steps at the sample inlet. At each gas pressure, the specimen reaches equilibrium as the gas pushes some of the liquid out of the specimen.
Visualisation and structural analysis of pore spaces in a shear zone sample.

X Ray Tomography

The image below (diameter 9mm) was record using X-ray tomography of one of the successfully removed rock cores. X-ray tomography is a non-destructive technique which allows us to visualise the inside of the rock cores without actually slicing them up. It is similar to CAT scans used in medicine and produces 2D slices. Click on the X-ray tomography picture to see these images linked up into a virtual trip through the core, the core is the lighter cylindrical shape in the centre and the darker areas observed in the core are pore space.

 

Laser Scanning Confocal Microscopy (LSCM) (Sandia Labs)

3D imaging with was carried out using Laser Scanning Confocal Microscopy (LSCM):

  • Illumination and detection are confined to a single location in specimen at any time
  • Improved resolution to theoretical limit set by Rayleigh diffraction (~0.2 micron)
  • Capability for optical sectioning (distribution of fluorescence intensity in xyz space)

A schematic of the instrumentation is shown below.

 

 

A schematic of the instrumentation is shown below.

GAM : Schematic of Instrumentation

 

This technique produces images which allow the surface porespace of the samples to be visualised. The image below is a low magnification view of region within several mm-wide macroscopic shear zone

 

GAM : Visualisation of surface poresapce

 

Higher magnification images can also be taken.

GAM : microcraking

Block-like microcracking in phenocryst within shear zone

GAM : sharp transition region with no porosity

High-resolution image illustrating sharp transition to region with no porosity
 

 

GAM : Region within macroscopic shear zone

Higher magnification view of region within macroscopic shear zone , illustrating bimodal porosity distribution within shear zone

 

Gas Migration in Shear Zones (GAM)

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.