Goldschmidt 2020

Iceland and the rapidly developing sustainability industries

At the junction of the Reykjanes rift and the south Iceland seismic zone (SISZ), Hengill is the center of extension, normal faulting, geothermal activity, and seismicity.

Why should we care about fluid-rock interactions?

The evolution of permeability in geothermal reservoirs is strongly affected by interactions between the host rock and the fluids flowing through the rock’s permeable pathways.

What did we do?

3D Model Building from Drone Imagery

Acquiring high-resolution images using drones allow us to identify and quantify the fracture patterns that control fluid flow in the area.

Due to the overlap of two regimes, an extensional regime from the rifting and the transform zone of South Iceland Seismic Zone, the fracture patterns have many different orientations and a big question arises:

Which fractures are connected and which aren’t?

Field structural mapping

Structural field geology helps us understand which fluids paths are likely to transport fluids. During several field campaigns we recognised the existing fracture patterns and fluid-rock interaction indicators along these fractures.

Left: WNW System sinistral foliation with eroding infill. Right: ENE System displaced by NS faults (dextral). The system appears to be synkinematic (they all cross-cut each other)

This work is been expanded by PhD student Ashley Stanton-Yonge as part of her PhD project. Expect more results to come in the near future!

Mineral analysis and microstructures

We examined cores from the Nesjavellir geothermal field. Courtesy of Reykjavik Energy and ISOR
Thin sections were observed with optic microscopy to investigate the microstructures and mineralisations on the core as a product of hydrothermalism.

Plane polarised light images from depths 880 m and 1454 m were characterised and an ImageJ script was used to map out the percentage of clays, oxides and other hydrothermal alterations present in the image.

These measurements were used to calculate how the porosity of the rocks have changed as a consequence of hydrothermal alteration.

This work was done by Callum Clark during his master’s thesis.

Experimental permeability  measurements

Laboratory experiments allow us to have a precise measurement of the permeability of the rocks of reservoirs. However, it also leads to carefully thinking the role of matrix permeability and fracture permeability in changing systems.

In UCL we use servocontrolled permeameters to quantify fluid flow through rock samples. Permeability values are then calculated by direct application of Darcy’s Law. This diagram has been modified from Benson et al., 2005.
Permeability of macro fractures with increasing effective pressure.

Upcoming research

Experimental design for in situ permeability evolution quantification

Finally, we aimed to investigate the permeability evolution of a single fracture during injection of CO2-saturated water under controlled CO2 inlet and outlet volume, pressure and temperature conditions. This experiments are delayed due to the current pandemic, but will be presented at a later date. This experimental design aims to constrain the rate of permeability changes of the system during both injection and carbonation stages.

This is a new technology designed and built in UCL, for more information about this technology you can get in touch with Dr Tom Mitchell and Dr Pedram Mahzari.

Stay tuned for our upcoming results!