Integration of micro-CT and NMR-based techniques for reservoir rock characterization

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Copyright: Shikhov, Igor
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Abstract
The petrophysical interpretation of 2D diffusion-relaxation NMR responses is a long-standing problem complicated by the complexity of sedimentary rocks as well as the properties of saturating fluids including crude oils and the ill-posedness of the underlying mathematical problem. We aim to improve the quality of petrophysical properties estimates, such as permeability, capillary pressure and relative permeability curves and fluid typing with the aid of NMR techniques using a combination of numerically simulated low-field NMR and μ-CT imaging techniques. In first instance we study in detail the NMR responses of complex fluids and the influence of environmental factors like oxygen saturation. A simulation strategy for the fluids themselves using a multi-component fluid consisting of independent components is developed. The distribution of fluids in sedimentary rocks depends on capillary pressure history. We simulate primary drainage on μ-CT digitized rock representations using morphological transformations. The approach is used for different potential functions to implement common capillary pressure techniques (porous plate, mercury porosimetry (MICP) and centrifuge multi-speed). We evaluate the influence of specific boundary conditions, the effect of image resolution, and compare to saturation profiles measured by NMR methods. We show good agreement for three sandstone rocks. Spatially-resolved NMR is used to estimate two-phase air-brine relative permeability. Using a simulated centrifuge (primary) drainage to set a gradient of partial saturations, a set of longitudinal relaxation time distributions is obtained on linearly-spaced subsets each emulating a volumetric point of MRI experiment. Simulated NMR-based relative permeability curves show reasonable agreement with experiment and to standard steady- and unsteady-state special core analysis (SCAL) techniques. Quantitative interpretation of NMR response from rocks containing crude is complicated. We model the NMR response of crude oil as a weighted mixture of distinctive components. Environmental effects like oxygen paramagnetic relaxation enhancement are corrected using experimentally established correlation to a carbon number. We show agreement between experiment and simulation for two sandstone rocks for fully and partially saturated systems, potentially paving the way for extending NMR-based relaxivity permeability techniques to samples saturated with crude.
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Author(s)
Shikhov, Igor
Supervisor(s)
Arns, Christoph
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Publication Year
2015
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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