Meeting future net-zero carbon energy needs: Improved borehole sealing using compacted bentonite and silica grout

Overview

This project will investigate new technologies for borehole sealing to prevent the upward leakage of fluids and gases that are stored at-depth in the ground. Reliable borehole sealing is vital for global development of an energy industry that can meet net zero carbon by 2050 (2045 in Scotland). The UK Committee for Climate Change predicts that future energy production will include: carbon capture and storage in subsurface reservoirs (to capture CO₂ emitted from hydrogen production); nuclear power production (and hence the ability to safely dispose of nuclear wastes in the subsurface); and subsurface hydrogen storage to meet energy needs when output from renewables is low e.g. in low wind speeds. To store wastes or gases in the ground, boreholes must be drilled for site investigation and/or gas/fluid injection. These must then be sealed to stop unwanted fluid or gas leakage. One method for sealing is backfilling the hole with bentonite, a clay which swells when wet to form a tight seal. However, recent trials have shown that in weak or damaged rocks, the borehole walls can collapse before the bentonite is put in place. This PhD project will investigate the potential for novel materials, such as silica hydrogels, to provide short-term stabilisation of weak rocks. The PhD will be based primarily in the laboratory. Depending on the skills and interests of the successful candidate, the research will involve: investigation of geotechnical properties; determination of chemical interactions between bentonite clay and hydrogels; investigation of performance using state of the art imaging techniques such as Micro X-Ray Computer Tomography and Scanning Electron Microscopy; numerical modelling of material performance. 

Methodology

The project will be largely experimental, using equipment in the University of Strathclyde’s geotechnical laboratories. Colloidal silica will be injected into samples of damaged mudstone and the resulting material will be tested for shear strength, erosion resistance and unconfined compressive strength. The chemical and physical interactions between the colloidal silica and the bentonite will also be investigated to determine any long-term impacts on seal performance. Investigations will make use of the University of Strathclyde’s Advanced Materials Research Laboratory, which hosts equipment such as Scanning Electron Microscopy, X-Ray Diffraction facilities and Micro X-Ray Computer Tomography. 

This project will suit a student interested in energy, geoscience, geotechnics, rock mechanics, geochemistry and/or material science using experimental techniques. You will learn basic laboratory techniques and will be trained on regularly used analytical equipment. As a PhD student at the University of Strathclyde, you will also complete the University of Strathclyde’s acclaimed Research development program, acquiring cross-disciplinary skills to broaden career prospects in various industries. The candidate may also undertake a short secondment to gain work experience at Nuclear Waste Services Ltd.