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Canberra, Australia

Regmi G.,University of Wollongong | Indraratna B.,University of Wollongong | Nghiem L.D.,University of Wollongong | Golab A.,Digitalcore Pty Ltd | Prasad B.G.,University of Wollongong
Journal of Environmental Engineering

Acidic groundwater generated from pyrite oxidation in acid sulfate (AS) soil is a major geoenvironmental problem in Australia. This study aims to evaluate recycled concrete as a reactive material in permeable reactive barriers (PRBs) for the remediation of acidic groundwater in low-lying AS soil floodplains. Laboratory experiments were systematically conducted to investigate the acid neutralization behavior of recycled concrete and its potential to remove dissolved Al and Fe. The results confirmed that recycled concrete could effectively treat acidic groundwater from an AS soil terrain, resulting in near neutral effluent over a long period with complete removal of Al and Fe. The major mechanisms involved in neutralizing acidic groundwater are thought to be the precipitation of Al and Fe as oxides, oxyhydroxides, and hydroxides. However, the accumulation of secondary minerals could decrease the reactivity of the recycled concrete. For example, chemical armoring could decrease the neutralizing capacity of recycled concrete by up to 50% compared with the theoretical acid neutralization capacity of this material. The results reported here also show that the neutralization capacity and reactive efficiency of recycled concrete are dependent on the initial pH value and also the concentration of Al and Fe in acidic groundwater. © 2011 American Society of Civil Engineers. Source

Fogden A.,Australian National University | Kumar M.,Digitalcore Pty Ltd | Morrow N.R.,University of Wyoming | Buckley J.S.,University of Wyoming
Energy and Fuels

The mounting evidence that waterflooding of clay-containing sandstone reservoirs using floodwater with reduced salinity can enhance oil recovery, but with unpredictably large variation in responses, demands improved understanding of the underlying mechanisms. Mobilization of clays and other fines is one candidate mechanism. Flow experiments in Berea sandstone plugs were designed such that the change in their fines distribution from before to after the oil and water injections could be imaged in exactly the same pores using scanning electron microscopy. This technique also allowed imaging of the wettability distribution on pore surfaces and was coupled to spectroscopic analysis of the adsorbed asphaltene amounts. One-phase flows switching from high- to low-salinity water led to only a low level of fines mobilization, compared to two-phase experiments in which high- or low-salinity water displaced crude oil from mixed-wet prepared plugs. The images reveal that loosely bound, partially oil-wet fines lining sandstone grains are stripped by the adhering oil during its recovery and redeposited on grains further downstream. Reduced salinity increases the fraction of fines thus mobilized by weakening their bonds to grains and strengthening their bonds to oil. Evidence suggests that these more oil-wet fines stabilize the water-in-oil curved menisci, which can aid in maintaining the connectivity of the oil phase and thus enhance oil recovery. © 2011 American Chemical Society. Source

Feali M.,University of New South Wales | Pinczewski W.V.,University of New South Wales | Cinar Y.,University of New South Wales | Arns C.H.,University of New South Wales | And 5 more authors.
SPE Latin American and Caribbean Petroleum Engineering Conference Proceedings

It is now widely acknowledged that continuous oil spreading films observed in two-dimensional glass micro-model studies for strongly water wet three-phase oil, water and gas systems are also present in real porous media and result in lower tertiary gas flood residual oil saturations than for corresponding negative spreading systems which do not display oil spreading behavior. However, it has not been possible to directly confirm the presence of spreading films in real porous media in threedimensions and little is understood of the distribution of the phases within the complex geometry and topology of actual porous media for different spreading conditions. This paper describes a preliminary study using high resolution X-ray microtomography to image the distribution of oil, water and gas after tertiary gas flooding to recover waterflood residual oil for two set of fluids, one positive spreading and the other negative spreading, for strongly water wet conditions in Bentheimer sandstone. We show that for strongly water-wet conditions and a positive spreading system the oil phase remains connected throughout the pore space and results in a low tertiary gas flood residual oil saturation. The residual oil saturation for the corresponding negative spreading system is significantly higher and this is shown to be related to the absence of oil films in this system. The presence of films for positive spreading systems and the absence of such films for negative spreading systems is further confirmed by the computation of the Eurler characteristic for each phase. Copyright 2012, Society of Petroleum Engineers. Source

Golab A.,Digitalcore Pty Ltd | Ward C.R.,University of New South Wales | Permana A.,University of New South Wales | Lennox P.,University of New South Wales | Botha P.,FEI Australia Pty Ltd
International Journal of Coal Geology

Samples of coal from the Sydney and Bowen Basins of eastern Australia have been imaged at high resolution using a large-field, 3D microfocus X-ray computed tomography (μCT) system, with special but not exclusive attention to evaluating the modes of occurrence of the mineral matter within the coal. The samples imaged were 110mm, 25mm, 19mm, 10mm, and 4mm in size, yielding voxel dimensions of 54, 30, 12, 6, and 3μm respectively. Data collection was carried out using a helical stage, providing images with >20002voxels in the horizontal (X-Y) plane and up to 3500voxels high. Three-dimensional image blocks derived from the scans were examined as cross-sections along orthogonal planes and as perspective images, manipulated to be viewed from any angle. Imaging after saturating the coal with X-ray attenuating brine was also carried out to highlight the distribution of connected micro-pores and cleats, and improve the detail of features seen within the samples.Features evaluated within the coals included the size and three-dimensional distribution of siderite nodules, and different types of mineral infillings in petrifactions of maceral components. Individual macerals could also be identified within the coal, based partly on X-ray density and partly on the associated porosity and structure. In some cases high-resolution images enabled the nature of individual plant particles to be identified within the coal samples. Mineral-filled cleats and open fractures were also evaluated, including the origin of radiating fracture patterns around siderite nodules in vitrinite. In some cases several generations of cleat and/or fractures could be distinguished, and the sequence of their formation and infilling was interpreted.Complementary analyses of the mineral matter in the samples were carried out using X-ray diffraction, as well as examination of polished sections by optical microscopy examination. Images obtained from the μCT scans were also registered against SEM-EDX and QemSCAN images of polished sections prepared from the same samples after scanning, providing a more definitive basis for identifying the different components and for integrating μCT data with results from other petrographic and electron microscope studies. © 2012 Elsevier B.V. Source

Kumar M.,Digitalcore Pty Ltd | Senden T.J.,Australian National University | Sheppard A.P.,Australian National University | Arns C.H.,University of New South Wales | Knackstedt M.A.,Digitalcore Pty Ltd

The saturation exponent, n, is often assumed to be two in the absence of core data, but a variety of " values have been reported. This uncertainty in n may be due to pore geometrical and topological complexities, structural heterogeneities coupled with variations in wettability. As values of " are correlated to oil-in-place, good estimates of n are needed. Recently, an X-ray μ-CT imaging registration technique was developed where multiphase fluid saturations can be measured in-situ on a pore scale basis within reservoir miniplugs. Using this technique, one can obtain information on the relative fluid affinity for specific pore regions, as well as the connate wetting phase saturations and habitat of the hydrocarbon and wetting fluid within the rock at the pore scale. From the observed fluid saturations one may use numerical simulations to predict the value of n and better understand reasons for deviations in the saturation exponent from the conventional values. In this paper, we describe analyses undertaken on both clastic and carbonate samples under variable saturation conditions. Coupling 3D imaging, high-resolution SEM analysis, and in-situ observations of fluid saturation enables one to understand the observed resistivity response of various samples under different saturation conditions. In a first set of experiments, we discuss the observed behavior on a clean water-wet sandstone; in experiments, one observes n ≈ 2 at high to intermediate water saturations (Sw), but at lower Sw, " < 2. Using a combination of μ-CT, image registration and cryo-SEM analysis we observe that at low Sw water films in those clean sands concentrate at or on the perimeter of grain contacts. 3D analysis shows the grain contacts span the rock structure. Simulation results show that the inclusion of a realistic thin water film within grain contacts results in a match to the measured behavior for RI. Analyses are also performed on carbonates under variable wettability conditions. The role of microporosity, wettability, and saturation history on pore scale fluid distributions and thus resistivity response is discussed. The results underline the potential importance of microporosity in determining saturation exponents at low Sw. Capturing porosity information at all scales gives better estimation of original oil-in-place, particularly for carbonates displaying a wide variety of pore structure and wettability behaviors. © 2011 Society of Petrophysics and Well Log Analysts. All Rights Reserved. Source

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