Enhancing Special Core Analysis Insights into Wettability through the Application of Magnetic Resonance
Energy demand is determined from a balance of affordability, sustainability and security. The oil and gas exploration and production industry has shifted focus to try and optimise production from existing hydrocarbon fields without substantially increasing emissions. Special core analysis aims to aid optimisation of improved/enhanced oil recovery (IOR/EOR) fluids to increase hydrocarbon production from existing fields by altering the wettability of the system. Wettability is the preference of a fluid to adhere to the surface of a rock core whilst in the presence of another immiscible fluid and can be quantified through special core analysis. This thesis aims to increase understanding of special core analysis protocol through the development and application of magnetic resonance (MR) methods and apply them to an IOR/EOR wettability altering corefloods. This was achieved by developing low-field techniques including the constant gradient *z*-*T*1-*T*2 and *z*-D-*T*2 and high-field 3D imaging of *T*1 and *T*2. The new methods were applied to a series of corefloods to ensure that they were quantitative. The previously established 2D *T*1-*T*2 correlation was quantitively benchmarked to the industry standard wettability measurement, the Amott-Harvey test. The first *in situ* monitoring of the ageing process was also conducted on crude oil samples. The findings indicate that the newly developed methods aligned quantitatively with the volumes produced that were determined through both existing MR techniques and gravimetric measurements obtained during corefloods. In addition, the methods provided increased data on systems through spatially-resolved *T*1/*T*2 (a measure of the strength of surface interactions) and spatially-resolved diffusion on the 2 MHz spectrometer when relaxation data did not give sufficient phase-separation. Benchmarking the 2D *T*1-*T*2 to the Amott-Harvey experiment for neutral- and oil-wet cores gave strong results and showed there was a correlation with the resultant wettability indices – for the oil-wet sample, oil *T*1/*T*2 was higher throughout and for the neutral-wet sample they were similar. For the crude oil experiments, clear evidence of common mechanisms occurring to all the rock types and fluids were seen, with macroscopic displacement dominating the early phase of the primary drainage experiments before microscopic displacement as irreducible water saturation is reached. During low-salinity IOR flooding, MR measurements provided evidence for wettability alteration without having to conduct a full Amott-Harvey experiment. This thesis has furthered core analysis protocol and understanding through the development of new techniques and applying them quantitively to complex corefloods to increase understanding of multiphase displacement mechanisms.
MRI, NMR, Oil and gas, Special core analysis, Wettability
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