hrvatski

Application of X-ray computed tomography (CT) in core sample analysis

X-ray Computed Tomography (CT) is a non-destructive method useful for investigation and 3D visualization of a wide range of materials, including rock, bone, ceramic, metal and soft tissue. Characterization of reservoir rocks is of utmost importance for production planning in oil & gas industry, so 3D imaging is a useful tool in the visualization, analysis and modelling of those rocks. Porosity, fluid saturation, and permeability derived from core can be tied to log response ; however, several studies have shown that the results obtained from different core analysis laboratories can vary significantly, reflecting differences in proprietary analytical protocols, differences in definitions of fundamental rock and fluid properties. The description of pore space especially in carbonate rocks is very important in the oil & gas industry because pores contain natural accumulation of producible hydrocarbons which is confined by impermeable rocks. Standard 2D methods for determination of porosity in rocks (CCA including thin section and helium porosymeter – Corelab method) are limited. CT is a non-destructive technique for visualizing interior features within solid object and for obtaining digital information on their 3D geometries and properties. This information has strong scientific interest (studying of fluids/ions migration, formation of properties) and can also be used in practice in different areas of oil & gas industry, e.g. for optimization of enhanced oil recovery (EOR) methods, analysis of mechanisms of reservoir formation damage, etc. This 3D quantitative analysis is essential because conventional 2D (thin-section) images cannot provide true porosity. CT scanner matched with compatible software is able to extract large amount of qualitative and quantitative information, based on which petrophysical parameters such as porosity, connectivity, and permeability can be calculated, visualized and applied in oil & gas investigation. To test CT method we have compared CT scans from medical (Siemens Somatom) and industrial scanners (Skyscan 1173) on a single sandstone sample. Industrial scanner proved to be more accurate because it has better resolution and can provide true results of micro porosity. Apart from use in oil & gas industry, CT obtained data have been applied to virtually every geological discipline, and new applications are being continually discovered. Successful applications to date include: – Measuring 3D size and spatial distribution of crystals, clasts, vesicles, etc. – Non-destructive volumetric study of rare specimens (fossils, meteorites, etc.). – 3D measurement of: fluid flow fields, including porosity (CP, OP and TP), microporosity, and fracture extent and roughness. Description and quantification of porosity and permeability in rocks and soils. – Porosity and permeability estimation of rocks intended for UGS facilities – 3D fabric determination (foliations, shape preferred orientations, network properties). – Inspection and measurement of morphology in fossils and recent biological specimens. – Detection and examination of high-density economic trace phases. – Reconnaissance imaging of samples for optimal geochemical exploitation (for example, locating crystal central sections, spiral axes, solid and fluid inclusions).

X-ray CT, core samples, porosity, permeability, EOR

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