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New insights into pore structure characterization and permeability measurement of fine-grained sedimentary reservoir rocks in the laboratory at reservoir stress states Letham, Eric


Fine-grained reservoir rocks are economically important because of the vast quantities of hydrocarbons they contain, but remain poorly understood due to how difficult it is to analyze their highly stress-sensitive, anisotropic, nanometer-scale pore systems in the laboratory. In this thesis, techniques for pore structure characterization and permeability measurement of fine-grained reservoir rocks at reservoir stress states are developed and tested. Klinkenberg gas slippage measurements provide accurate measurements of pore size. The gas slippage technique has many valuable characteristics, such as the ability to measure pore size at reservoir stress and to quantify anisotropy of pore geometry. In addition to pore size, matrix permeability is quantified when measuring gas slippage. The gas slippage technique developed in this thesis provides important petrophysical information about fine-grained reservoir rocks that cannot be acquired using other commonly applied pore structure characterization techniques. A technique to semi-quantitatively determine permeability-effective stress law coefficients is developed by analyzing Klinkenberg plots of permeability measurements made at a wide range of confining pressure and pore pressure. This semi-quantitative technique is important because other fully quantitative techniques that are typically applied to coarse-grained reservoir rocks result in erroneous effective stress laws when applied to fine-grained rocks; in the nanometer-scale pores of fine-grained rocks, gas slippage results in significant permeability variation with pore pressure that is independent of changes to pore geometry, and therefore results in erroneous permeability-effective stress laws. A technique for determining the effective permeability of fine-grained reservoir rocks at different fluid saturations is developed by measuring ethane gas permeability at a range of pore pressures up to the saturated vapour pressure of ethane at laboratory temperature. Liquid/semi-liquid ethane saturation increases with increasing pore pressure due to adsorption and capillary condensation, resulting in restricted fluid flow pathways and hence decreased effective permeability to ethane gas. Ethane gas permeability measurements can be made at different stress states to investigate the sensitivity of effective permeability to stress at the range of stress states experienced during production from a fine-grained reservoir.

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