A better understanding of the brine-rock- supercritical CO2 interaction is needed to evaluate the risks of geologic CO2 sequestration. The geochemical effects of brine and supercritical CO2 were examined via laboratory modeling of in situ conditions on two reservoir caprocks in the Black Warrior River Basin, the Pottsville and Parkwood Formations. The clay fraction was extracted and treated at ~ 100 bar and 363 K (90 °C) over periods of up to 70 hours. Supercritical CO2 was introduced as dry ice in a pressurized vessel. Samples were observed using XRD, WD-XRF, AA, SEM, and EDS. Clay fractions contained Fe-chlorite, illite, kaolinite, and quartz. Results show the dissolution of illite, CO2-brine induced cation exchange ok K+, and the dissolution of silicate minerals. Steady-state K/Si ratios in the fluid suggest quartz re-precipitation. These interactions could adversely affect the long-term storativity of the caprock and point to a need for further study.

M.Sc.(Eng.), Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2011

No description available.

Coal Seam Gas (CSG) is a form of natural gas (mainly methane) sorbed in underground coal deposits. Mining this gas involves drilling a well directly into an underground coal seam, and pumping out the water (CSG water) flowing through it. Presently, CSG is under exploration in New Zealand (NZ); however, there is concern about CSG water disposal in NZ mainly because of the controversy that this activity has generated in some basins in the United States (US). The first part of this thesis studies CSG water from a well in Maramarua (NZ) and compares it to water from US basins. The NZ CSG water from this well had high pH (7.8), alkalinity in the order of 360 mg/l as CaCO₃, high sodium (334 mg/l), bicarbonate (435 mg/l), and chloride (146 mg/l). These ions also occur in US CSG waters, and their concentrations follow the same trend - high sodium, bicarbonate, and chloride with low calcium, magnesium, and sulphate concentrations. Prior to this work, little detailed analyses of CSG water quality variability from a well had been carried out. A Factor Analysis of 33 Maramarua samples was conducted and revealed that about one third of the variations were due to sample degassing, which induced calcium carbonate precipitation - this was supported by experimental work (sample sparging) and geochemical modelling (MINTEQA2). This finding is important for CSG water management because, as calcium concentrations decrease, higher SAR values are generated, and this can cause problems if CSG waters are disposed on land. In the second part, this thesis assesses the potential environmental effects of disposing CSG waters in NZ by formulating management options and a simple wastewater treatment system. This was carried out by studying the ecological response (soils, plant, and aquatic life) resulting from CSG water disposal operations in the US, and by applying relevant salinity and sodicity guidelines to the interaction between soils and CSG waters from Maramarua. This work showed that similar problems are likely to occur in NZ if CSG water disposal takes place without proper controls. Such a study has never been carried out in a region before actual CSG development has taken place, so this work shows how to quantify the effects arising from CSG water disposal prior to full scale production. This can be particularly useful for CSG stakeholders wanting to develop this resource in other regions around the world. A simple treatment system using Ngakuru zeolites has proven effective in reducing the SAR of Maramarua CSG water. Laboratory results indicate that these zeolites work by exchanging sodium cations in the water by other cations contained within the zeolite structure but with slow ion exchange kinetics. The calculated sodium absorption capacity for these natural zeolites ranged from 11.3 meq/100g to 16.7 meq/100g (flow-through conditions without previous regeneration). In addition, these experiments showed that the ion exchange process is accompanied by some dissolution (sulphate, boron, TOC, sodium, calcium, magnesium, potassium and reactive silica), but mainly at the beginning of the treatment process. Nevertheless, using this system, 180 grams of zeolite material were used to treat an initial 1.83 litres of Maramarua CSG water thus reducing potential soil infiltration problems to nil. As more CSG water was treated, the zeolites kept reducing SAR values but at a lesser rate until 4.53 litres of CSG water had been treated. A step-by-step methodology to assess treatment design options for these materials has been developed and will aid future researchers and engineers. This thesis presents the first comprehensive study of CSG water management in NZ. It also presents an ion exchange treatment system using natural zeolites already available in NZ. In conclusion, the research finds that, whether through adequate management or active treatment, CSG waters can be safely disposed without creating major environmental problems, and can even be used in beneficial applications.

This study is informed by the rising demand for power needs in South Africa and aims at understanding the geophysical and geochemical characteristics of the energy minerals in the Springbok Flats Basin and relating them to the prevailing geological and structural setting for improved exploration targeting. The Springbok Flats Basin is part of the Karoo sediments and host to uranium, coal and coal bed methane (CBM) resources. The lithology sections in the basin indicate presence of basaltic lavas at the top, underlain by mudrocks, siltstones, sandstones, conglomerates and diamictite, with interbedded coal beds occasionally. The coals are uraniferous and shale bounded and of lower Beaufort age at 250 Ma. The regional radiometric data identifies the regional extent of the Springbok Flats Basin as a basin with low total count values. This information is useful in exploration as it gives an idea of the limits of the area where to focus application for prospecting licenses. The reduced to pole of the total magnetic field, residuals and first vertical derivative maps clearly show the high magnetic susceptibility nature of the surrounding Bushveld rocks as compared to the low Karoo sediment susceptibility within the basin. There are distinct ring shaped picks within the basin possibly due to known Karoo dolerite sills in particular to the central south western part of the grid. The regional geochemical mapping program is a cost-effective way of providing an overview of the relative abundance levels, regional trends and anomalous patterns in the underlying lithological units. Background values of elements in soils over different lithological units and the identification of anomalous values relative to these elements can easily be identified. The geochemical results show an excellent correlation between soil chemistry and underlying geological formations. A few distinct gravity highs are clearly shown within the basin. Assuming the effect of the Letaba basalt to the gravity readings is uniform across the basin; these distinct anomalies could be due to Karoo dolerite sills as they coincide with areas of distinct high magnetic signature. A conceptual model was generated assuming that the Karoo sediments’ layering is uniform across the gravity profile but changes in the residual are due to an increased thickness of the sill supported by the gentle changes on the surface topography. Satellite imagery has got its challenges especially in areas of vegetation but it does provide a very useful tool in exploration. A number of spectral analysis techniques and band rations can be used to differentiate the areas underlain by the Letaba basalts, the Karoo sandstones/shale and Bushveld granites for mapping purposes. The priority focus will be on the shallower Karoo sediments because of the potential for cheaper mining. Exploration targeting needs to be guided by observed geochemical and geophysical characteristics in order to prioritize areas taking into account the presence of Karoo intrusives such as the dolerite sills that tend to devolatize the coal hence affecting the quality/rank. Structures and gravity signatures are very important in delineating areas with thick sediments that have a potential for CBM. The same understanding in targeting goes a long way in planning drill holes, resource modelling and pre-feasibility stages for mine planning. A high resolution airborne geophysical survey is recommended over the basin to better resolve structures. Geophysical borehole logging is recommended to be part of the exploration drilling programs in the Springbok Flats Basin in order to define the in-situ geophysical characteristics. Geophysical logging is useful in particular for the uranium reserves that cannot be delineated from the surface due to deep intersection.