Our Graduate PhD Students

The main aim of this study is to propose a modified 3-dimensional numerical model using the discrete element method (DEM) that enables interpretation of mechanical behavior, and the variation of water distribution, in unsaturated granular materials with low saturation degree. By modelling monodisperse packings incorporating with well-defined rules of water distribution and the elementary laws under an external load, macroscopic behaviours and stress-strain relationships of unsaturated soil can be more accurately simulated along a set of increasing water content. To demonstrate the modelling results, experiments using X-ray computed tomography (X-ray CT) are conducted for observations of the amount and spatial distribution of capillary bridges at low water content. The origin of capillary strength is analyzed by carrying out the microscopic investigations.

Many geophysical survey techniques rely on making high-precision measurements of gravitational forces and magnetic fields. New quantum sensors that exploit the properties of cold-atom systems offer sensitivities that surpass existing classical instruments. There has been recent rapid progress in making such sensors small enough to deploy in the field. However, further miniaturisation towards hand-held devices will require the design and fabrication of next-generation atom chips and optical components. Inverse methods will be of crucial importance both for predicting the chip geometries required to control the atoms and for interpreting the data obtained from the deployment of sensor arrays. The project will use established collective expertise at BGS and at the University of Nottingham to develop the inverse-method modelling, use it to design and analyse the sensor performance, and then interpret data obtained from sensors and sensor arrays as they become available.

This research aims to identify the current status and future prospects for CCS development and deployment in the People’s Republic of China. By identifying Chinese and international CCS stakeholders and an analysis of international activity and communications on CCS-related activities with China, this research aims to investigate the influence and impact of international institutions, programmes and projects, as well as personal interactions on China’s adoption of key CCS technologies and CCS-related policy formulation. Key to this research, however, are the efforts made by China in overcoming the barriers and obstacles to CCS development and deployment and how through social learning such advances are communicated and disseminated globally.

Yang, L., Zhang, X. and McAlinden, K.J., 2016. The effect of trust on people's acceptance of CCS (carbon capture and storage) technologies: Evidence from a survey in the People's Republic of China. Energy, 96, pp.69-79. Available Online at: http://www.sciencedirect.com/science/article/pii/S0360544215016862

Yang, L., Yao, Y., Zhang, J., Zhang, X. and McAlinden, K.J., 2015. A CGE analysis of carbon market impact on CO2 emission reduction in China: a technology-led approach. Natural Hazards, pp.1-22. Available Online at: http://link.springer.com/article/10.1007/s11069-015-2122-y

Read Dr Giannoukos' thesis on Nottingham eTheses

Several faults can be observed at the borehole cement used in the geological CCS, that might constitute precursors of favourable paths for CO₂ leakage. Potential pathways for leakage can occur through the grout of the annular cement or the cement sheath, or via either the cement-rock (CR) or the cement-steel (CS) interfaces. As a consequence the assessment of the impact of carbon dioxide species in the grouts is imperative for the prediction of their long term behaviour at subterranean storage conditions. Being the most important parameter of borehole cements, porosity influences not only the profile of carbonation propagation fronts of the grouts but also exhibits particular reactive characteristics in the CS and CR interfaces; hence its time evolution is essential to better understand how well sealing capacity can be secured for long-term storage of CO₂ allowing the primary leakage risk of CCGS to be better managed.

Giannoukos, K. et al. 2014. Preliminary Investigation on the Chemical Response of Cementitious Grouts Used for Borehole Sealing of Geologically Stored CO2. Energy Procedia.[online]. 59, pp.174-181. Available from: http://www.sciencedirect.com/science/article/pii/S1876610214017317 

Read Dr Lacinska's thesis on Nottingham eTheses

The type of feedstock and host rock utilised in ex situ and in situ Carbon Capture and Storage by Mineralisation (CCSM) is an important aspect of these technologies, and detailed appraisal of candidate mineral/rock performance in the presence of CO2 may greatly improve CCSM efficiency. Here, a detailed mineralogical and geochemical investigation of serpentine minerals and ultramafic rocks under laboratory-controlled experiments simulating ex situ and in situ process conditions is presented.

Feedstock serpentine minerals were analysed comprehensively, prior to experimental processing. The identification of antigorite was unequivocal using a combination of X-ray diffraction, Fourier Transform Infrared Spectroscopy and/or Thermo-gravimetric Analysis. However, the analysis of chrysotile and lizardite proved to be more challenging, especially when the two polymorphs were finely inter-grown. This study highlighted the structural, textural and chemical complexity of serpentines and showed that great care must be taken when analysing this mineral group for CCSM.

Investigation of the acid leaching of serpentine minerals under conditions of 70°C and 1.4M NH4HSO4 provided fundamental insights into the rate and extraction efficiency (EE) of Mg2+ and associated controlling factors, under conditions relevant for ex situ CCSM. It is demonstrated that EE is a function of mineral reactivity and depend on a complex interplay between crystal structure and chemistry. Generally, poorly crystalline and highly disordered phases with low levels of Al3+ were found to be suitable feedstock materials for acid digestion pre-treatment. Chrysotile, lizardite 2H1 and poorly crystalline serpentines showed up to 85% Mg2+ EE after 3 h of acid leaching, and hence are recommended as best feedstock materials for CCSM, whilst antigorite and Al3+-rich serpentines proved to be largely unsuitable, showing low levels of EE of ~ 20%.

Examination of dunite, harzburgite and serpentinite under conditions relevant for in situ CCSM, i.e. 70°C and 100 bar CO2 pressure, provided insights into rock reactivity as a function of composition and texture, and the progression of in situ mineral carbonation. The rate of net Mg release and thus the extent of subsequent carbonation were greatest for serpentinite, providing ca. 3% carbonation after six months. However, mineral reactivity within serpentinite was preferential, i.e. significantly enhanced within secondary vein serpentine, being thus, the main source of Mg2+ for magnesite precipitation. Reaction-induced transformation and hence mineral carbonation of dunite and harzburgite were less pronounced over the same time-scale. The reaction of serpentinite with wet supercritical CO2, as opposed to CO2-saturated brine, significantly affected rock integrity, with the exposure of more surface area and promotion of fluid-rock interaction. In particular, it is shown that ferric iron oxidation and the precipitation of goethite impacts upon surface mineral dissolution at exposed surfaces, thereby hindering subsequent carbonation. Overall, this study highlighted the importance of host rock choice for in situ CCSM and the need for detailed petrographical and geochemical investigation of any proposed CCSM repository prior to technological process modelling. 

The use of calcium oxide as a regenerable sorbent for CO₂ capture has been a subject of diverse research because of the enormous benefits it offers towards decarbonising the power industry particularly for post-combustion CO₂ capture applications. However, calcium looping technology has its own shortfall which is mainly sorbent deactivation with increasing loop cycle number, a consequence of mainly sorbent sintering and to a lower extent fragmentation. This research aimed to understand the role played by mineralogy and micro-structural properties of precursor limestone on the sintering ability and attrition of the resultant CaO sorbent post-cycling in order to inform material selection and to utilise naturally occurring heterogeneities. This was to form a possible standard for screening limestone samples to ascertain their suitability for calcium looping.  

Understanding attitudes toward new technologies such as carbon capture and storage (CCS) is critical to their long-term success. I investigated differences in perceptions of CCS based on differences in information provision, communication style, search strategy and personality characteristics. Support for CCS is chiefly governed by stable personality traits and value-beliefs; individuals seem to respond to persuasive communication but not to differently balanced factual information.

The concentration of CO2 in the atmosphere has increased by approximately a third since in the 1850s, the principal reason for this being the burning of fossil fuels. Storage of CO2 in underground geological formations is a potential means of limiting greenhouse gas emissions to the atmosphere while continuing to use fossil fuels. CO2 is injected seep into a storage site where, over time, it dissolves into the fluid saturating the rock. This process increases the density of the liquid, making the mixture sink, resulting in the formation
of large plumes of CO2-rich fluid. Over long time periods, reaction of the CO2 with minerals in the storage site can result in the precipitation of solid carbonates providing a more secure storage mechanism which limits the possibility of leakage to the surface.

Motivated by processes occurring during CO2 sequestration in an underground aquifer, we examine the effect of CO2 dissolution on the motion of the fluid. Using numerical modelling we see that storage sites
that induce convective motion in the fluid enhances the mixing process, thereby increasing the storage rate CO2. However, uncertainties in the physical and chemical structure of the host rock make modelling the problem complicated. The convective plumes that form incorporates flow varying over different length-scales, which when coupled with reactions varying over widely disparate time-scales places great demands on computations attempting to integrate chemistry and flow. There is therefore significant interest in deriving
simplified models that accurately capture the physical balances of the flow.

The main focus of this project is to use numerical simulations to derive approximate theoretical models of the mixing processes which in turn provides useful insights into the storage capacity of potential storage sites.

Dissolution-driven porous-medium convection in the presence of chemical reaction, T.J. Ward, K.A. Cliffe, O.E. Jensen and H. Power, Journal of Fluid Mechanics, vol. 747, pp. 316-349, 2014. Available from: journals.cambridge.org

High-Rayleigh-number convection of a reactive solute in a porous medium, T.J. Ward, O.E. Jensen, H. Power and D.S. Riley, Journal of Fluid Mechanics, vol. 760, pp. 95-126, 2014. Available from: journals.cambridge.org 

Substrate degradation in high-Rayleigh-number convection, T.J. Ward, K.A. Cliffe, O.E. Jensen and H. Power, Physics of Fluids (Under review), 2015