Neutron and X-ray 3D and 4D imaging of fluid transport within natural and lab-deformed carbonate rocks
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Carbonate reservoir rocks are characterised by complexities in their void space caused by various processes involved in deposition and diagenesis occurring through chemical dissolution, reprecipitation, dolomitization, fracturing etc. These complexities affect the transport properties of these rocks and hinder an accurate estimation, and therefore all ensuing simulation, of their hydraulic behaviour. This PhD aims to deepen understanding of the influence of core-scale complexities of the pore system of carbonate rocks on fluid transport properties and processes. For this purpose, the complementary capabilities of X-ray and Neutron imaging along with quantitative image analysis are employed to experimentally investigate the miscible and immiscible fluid transport processes within carbonate rocks. Different types of textural variations due to the depositional and mechanical deformational features within four types of carbonate rocks, Coquina limestone, Biolithite, Travertine and Oolitic limestone are first characterised by analysing X-ray micro-CT images acquired from dry samples. Then, a series of High Speed Neutron Tomographies (HSNT) are acquired during miscible and immiscible fluid flow experiments in the selected carbonate rock samples (38mm diameter core) to explore different fluid transport processes affected by the characterised core-scale features. Image analysis techniques are employed that allow the extraction of quantitative data of pore system properties and fluid transport from the captured X-ray micro-CT images and HSNTs. The analysis on X-ray micro CT images revealed the significant influence of features like fractures, lamina or layering, layering orientation and different types of textural variations on the pore network properties like porosity, permeability, pore connectivity and tortuosity. The fluid transport processes and properties including morphology of the flow patterns, fluid speed distribution, saturation/relative concentration distribution of fluid phases, capillary heterogeneity trapping and fracture-matrix flow were resolved using the combination of HSNT and quantitative image analysis. The results also provide important insight on miscible transport processes including irregularity in the advancing fluid front and longitudinal dispersion.