Society of Core Analysts 2017 Annual Symposium

The asphaltene fraction of crude oils is one of the main factors defining wettability conditions and ultimate oil recovery. At reservoir scale asphaltenes may cause reservoir compartmentalization and at pore scale govern wettability phenomena. To reproduce reservoir conditions, aging in oil is a common step in laboratory core analysis. Oils relevant to the origin of the plugs are the apparent choice for aging, while for outcrop rocks various hydrophobic chemicals and anti-wetting agents or arbitrary oils are often used. We evaluate alteration properties of synthetic oils represented by various proportions of commercially available bitumen, aromatics and alkane for studies requiring wettability alteration.Low-field NMR relaxation measurements have been applied in the past to characterise the wettability of rocks by introducing an NMR wettability index. However, the latter requires multiple reference measurements at end-point saturation states. NMR correlation techniques have a higher prediction capacity, e.g. T2-store-T2 (REXSY) experiment is naturally sensitive to spatial variation of physical properties by detecting diffusion exchange between different environments. It has been applied to study the connectivity of the pore space in aqueous systems such as gypsum, cement pastes, soils, etc. We applied REXSY to study effect of asphaltenes deposition on wettability of siliceous systems. The change of wettability over aging time in different synthetic oils was tracked using T2 relaxation measurements, providing estimates of aging dynamics useful in designing wettability-related experiments. Quantitative information about fraction of altered surface area and deposition pattern was inferred from combination of T2 experimental and numerically simulated responses and from T2-store-T2 experiments.Results show that the wettability alteration process is strongly sensitive to both chemical composition of synthetic oils and asphaltenes origin (light or heavy oil). It can be performed in controlled manner to set variety of heterogeneous wetting conditions. Elements of resulting deposition pattern and wetting state of the core were identified using low-field NMR relaxation and relaxation exchange techniques

Experimental and Numerical Investigation on Stress Dependence of Sandstone Electrical Properties and Deviations from Archie's Law

Resistivity Index (RI) of Fontainebleau and Bentheimer sandstones was investigated at ambient and reservoir pressures down to low water saturations using the porous plate method. The measurements compared with computations directly on high-resolution three-dimensional images of the pore space using Digital Rock Physics. The numerical computations are in reasonable agreement with the experimental measurements down to water saturations as low as Sw = 10 %. The RI measurements show that both sandstones display Archie behavior at elevated pressure. However, at ambient pressure the RI for Fontainebleau sandstone deviates from Archie behavior at low water saturations. The pore-space images suggest that the deviation from Archie behavior is due to the presence of conductive percolating grain contact regions. Bentheimer sandstone for which grain contacts do not percolate, displays Archie behaviour both at ambient and elevated pressures. The present study extends previous work on RI of clean sandstones using micro-CT based analysis to high confining pressures and shows that for such sandstones the RI at elevated pressure displays Archie behavior down to low water saturations

Humidity Effects on Effective Elastic Properties of Rock: An Integrated Experimental and Numerical Study

The surface energy of minerals increases due to a loss of humidity. In rocks this leads to strains without applying external stress (stress-free strain) and affects the rocks' elastic response. We utilize finite element calculations on X-ray micro-CT images to analyze the extreme cases of surface energy contributions and no surface energy contributions for the small strain case. Including surface energy utilizing published surface energies of quartz significantly increases the simulated bulk modulus. Grain contacts are considered perfectly cemented and therefore do not contribute to this difference. Confining pressure is not applied in the experiment to estimate the impact of surface energy to avoid the effect of grain contact slippage due to different stress paths. In addition, we compare simulated moduli with experimentally determined parameters. In this case, we incorporate confining pressure in the experiment since grain contacts are not considered in the simulation. The main reason to use confining pressure in the experiment here is to close the grain contacts with a view that the resulting porosity reduction is negligible

Gradient-based fibre detection method on 3D micro-CT tomographic image for defining fibre orientation bias in ultra-high-performance concrete

Ultra-high-performance fibre reinforced concrete (UHPC) is a class of advanced cementitious composites characterized by its high compressive and flexural strengths, toughness and enhanced durability. The mechanical properties of the UHPC are to a great extent dependent on fibre volume fraction, orientation and distribution within the cementitious matrix. However, determination of the true three-dimensional fibre orientation and distribution is challenging. In this paper micro-computed tomography (micro-CT) is used to determine these parameters. Cylindrical samples of UHPC were extracted from a dogbone tension test specimen and from a pretensioned bridge girder, and high-resolution micro-CT images were then acquired. Using the scanned data, and following three-dimensional image reconstruction and image processing, quantitative fibre information was obtained via a novel image post-processing technique based on local-intensity gradient significantly improving cross-fibre detection compared to existing techniques. The estimated fibre volume fraction is close to design and experimentally measured values. Straight and hooked end fibres in UHPC sample were successfully identified and segmented using this novel technique. The test results show the fibre arrangement to be highly anisotropic with fibres aligned predominantly in one direction, which is attributed to the casting processes and flow

Proceedings of iCMEMS Conference 2017

The strength and behaviour of coke at high temperatures has a huge impact on its performance in the ironmaking process. Prior studies reporting the effect of temperature on the failure stresses of cokeshave not always shown consistent trends owing to differences in sample sizes, properties, and testing methods. In the present work, a high-CSR Australian coke was subjected to high-temperature mechanical tests using a unique high-temperature test facility at ANSTO to determine its compression strengths and the associated microstructural and mineralogical modifications. X-ray diffraction analysis and micro-CT analysis were used to determine the mineralogical and microstructural changes in the cokes after testing. The work showed that there were three regimes of deformation in the coke with increasing temperature. Furthermore, the work showed that compression strengths of the cokewere higher at elevated temperatures in comparison to the observed values at room temperature. Microstructural analysis showed an increase in the extent of porosity after high-temperature testing owing to the in situ reduction of ash species in the coke. With increase in temperature, it is expected that glassy phases formed by ash fusion as well as increased graphitisation assist in enhancing plastic flow, which contributes to an increase in strength of the coke samples at these temperatures. However,with increasing graphitisation extents, the load-bearing capacity would decrease, leading to a lowering of the maximal strengths at the top temperatures. The findings provide an improved understanding ofthe mechanisms affecting high-temperature strength development in cokes and can further assist in correlations the strengths with variations in coke and parent coal characteristics

A comparison between the characteristics of a biochar-NPK granule and a commercial NPK granule for application in the soil

Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not return a profit to farmers due to the costs of application and the loss of NPK from soil in various ways. Thus, a combination of NPK granule with a porous biochar (termed here as BNPK) appears to offer multiple benefits resulting from the excellent properties of biochar. Given the lack of information on the properties of NPK and BNPK fertilizers, it is necessary to investigate the characteristics of both to achieve a good understanding of why BNPK granule is superior to NPK granule. Therefore, this study aims to investigate the characteristics of a maize straw biochar mixed with NPK granule, before and after application to soil, and compare them to those for a commercial NPK granule. The BNPK granule, with a greater surface area and porosity, showed a higher capacity to store and donate electrons than the NPK granule. Relatively lower concentrations of Ca, P, K, Si and Mg were dissolved from the BNPK, indicating the ability of the BNPK granule to maintain these mineral elements and reduce dissolution rate. To study the nutrient storage mechanism of the BNPK granule in the soil, short- and long-term leaching experiments were conducted. During the experiments, organo-mineral clusters, comprising C, P, K, Si, Al and Fe, were formed on the surface and inside the biochar pores. However, BNPK was not effective in reducing N leaching, in the absence of plants, in a red chromosol soil