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CON Bioconservation

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Oil and gas naturally occurs in the subsurface, in reservoirs that are composed of different rock types or lithologies. To be able to extract these hydrocarbons, certain properties of the subsurface rocks must be known, i.e. porosity and permeability. Porosity is defined as the volume of void space within a rock, typically expressed as a fraction or a percentage. Fluids or hydrocarbons are usually stored in the void spaces within the rock structure. Permeability describes the ability of such fluids to flow through rocks. These properties vary depending on several factors such as the process of deposition, composition, and post depositional processes such as diagenesis. Determining these properties for reservoir rocks is not as straightforward as it may seem, especially since its expensive to obtain samples of subsurface rocks that can be at a depth of a few kilometers. The discovery of oil fields within continental carbonate deposits (a calcareous rock type that originates on land) in the Campos basin, offshore Brazil is a perfect example of this. Unlike the more common reservoir rocks such as sandstone or marine carbonates, continental carbonates are characterized by a very complex pore structure. Therefore, the relationship between porosity and permeability in continental carbonates is not as well defined. This led to extensive studies of reservoir analogues such as quarries or outcrops on the surface of the earth that approximate the characteristics of subsurface reservoirs. Defining the flow properties of a rock is a time consuming and expensive process, which is why several geologists have tried to define this relationship through more convenient methods. Several successful approaches have been made in describing the relationship between porosity and permeability in rock types with a simple pore structure, such as sandstone and marine carbonates. This done by linking the geometry of the pore structure such as dominant pore sizes(DOMsize), pore complexity (PoA (2D) or SSA (3D), shapes and pore orientation to permeability. Similarly, this study focuses on defining the link between the geometry of the pore structure and permeability in continental carbonates. This is done by obtaining similar pore geometry parameters in both a 2D and 3D aspect. The 2D analysis is done through a digital image analysis (DIA) technique conducted on thin section images of rock samples, while in 3D these parameters are obtained by micro-computer tomography(microCT). The main goals of this study are to define the relationship between the previously mentioned pore geometry parameters and permeability, compare the findings of this research to previous work conducted on less complex pore structures, such as that of sandstones or marine carbonates and lastly, to compare the feasibility of using 2D digital image analysis in comparison to 3D microCT analysis. The results obtained in this study reflect certain similarities and differences. The relationships between the pore geometry parameters such as dominant pore sizes(DOMsize) and complexity of the pore space (PoA(2D) or SSA(3D) is present, however the relationship between pore geometry parameters and permeability is not as distinct in continental carbonates in comparison to less heterogenous lithologies, such as sandstone and marine carbonates. Furthermore, the results obtained via 3D microCT analysis provided more accurate descriptions of the pore structure and lead to better results in comparison to 2D DIA.