Projects

Projects: Projects for Investigator

The main objective of this proposal is to determining the nature and kinetics of fluid-rock interactions between CO₂-rich brines and rocks, in field settings as well as in laboratory experiments, in order to formulate and test models of the behaviour and fate of CO₂ injected in geological strata. To do this we need to determine the processes which moderate the fluid-mineral reaction kinetics, particularly the nature of the processes which result in much more sluggish kinetics in field settings compared with the predictions from laboratory experiments. The ultimate objective is to create a database and methodology that enables the results of this study to b e used in risk assessments and performance modelling of geological carbon storage sites.

To achieve these main objectives we will need to carry out the following:

1. Evaluate natural (CO₂ natural gas reservoirs) and anthropogenic (CO₂ injection EOR - Enhanced Oil Recovery) sites as analogues for geological CO₂ storage. As necessary, determi n e the hydrology and the nature of the CO₂-fluid to reservoir brine interactions in these sites and characterise the reservoir mineralogy, mineral characteristics that might control reaction rates (e.g. mineral surface areas and topologies) and fluid-mineral reactions by using a range of mineralogical, geochemical and isotopic analytical techniques.
2. Carry out laboratory expe r i ments on reservoir materials, cap rocks and single minerals to investigate mineral-fluid reactions and reaction kinetics under controlled conditions and to test the reactions and reaction kinetics inferred from the field-scale studies.
3. Perform laboratory experiments to make detailed measurements of noble gas solubility in, and partitioning between, supercritical and liquid CO ₂ and brine and extend the data available for the natural analogues to include high precision noble-gas isotopic and concentration data. This data will inform modelling of the hydrology of the natural CO₂ reservoirs.
4. Utilise existing and develop improved thermodynamic modelling of both equilibrium and kinetically-rate limited mineral-fluid reactions to a) relate there sults of field-based and laboratory experiments, b) enable more general application of the results from this and other studies to specific field sites and c) use the laboratory and field results to test the applicability of widely used thermodynamic models for mineral reaction rates.

This proposal is to use natural geological examples to evaluate the fate and ultimate safety of disposing of carbon-dioxide deep underground in geological formations. Separation of carbon-dioxide from power station fuels or exhaust products, and the injection and storage of the CO₂ underground in geological formations is an economical and practical way for global society to manageenergy supplies while transforming to a low carbon economy. The existence of geological sites where natural carbon-dioxide has remained stored for millions of years suggests removal for more than the 10000-year period needed to protect climate maybe practical and safe. However the processes which govern the fate of carbon-dioxide in brine-filled aquifers are complex and to guarantee the safety and efficiency of  the storage it is necessary to be able to predict these over the ~ 10000 year storage period, a time much longer than industry currently models reservoir processes.

Many of the processes which operate on supercritical or gaseous carbon-dioxide underground may enhance its storage potential. The buoyant CO₂ will dissolve in the formation brines to form denser CO₂-saturated brine which will sink. The CO₂-saturated brine is relatively reactive but current models suggest that the reactions with carbonate and silicate minerals in the reservoir will ultimately lead to a significant proportion of the CO₂ being precipitated as carbonate minerals stored permanently. However the CO₂-charged brines may also reactwith the caprocks which retain the carbon-dioxide and it is not known whether this will enhance the seals by mineral precipitation or degrade them by mineral dissolution. A major limitation in our ability to predict these fluid-mineral reactions is that the reactions proceed slowly at variable rates (days or months to many years) and our knowledge of the reaction rates in real field settings isvery limited. This project will study fluids and gasses from natural carbon-dioxide reservoirs and, where possible, from sites where carbon dioxide is being actively injected underground, to determine the rates of the mineral-fluid reactions in natural settings. We will duplicate the reactions in laboratory experiments where it will be possible to study the processes under controlled conditions,study individual reactions from the complex set of coupled reactions which take place in the natural rocks and examine the effects of varying potential rate-controlling parameters. The ultimate objective is to inform site assessment, risk and monitoring for geological carbon storage. The research will benefit other areas of the environmental sciences where rates of kinetically-limited fluid-mineralreactions govern important processes.