NMR assisted capillary pressure and water saturation measurements have proven to be significantly faster than traditional porous plate and centrifuge methods. The NMR directly measures water saturation along the length of the core and associated capillary pressure generated at a given centrifuge speed. It overcomes limitations of requiring lengthy equilibration times, tedious material balance, and approximate solutions. However, limited data is available with respect to actual application and operating range of the technology in reservoir cores. The objective of this study is to evaluate data quality, identify best practices, and any limitations in utilizing the faster NMR derived capillary pressure curves when compared against the gold standard porous plate method.
Core samples from a sandstone reservoir were selected to test a permeability range between 400mD – 1600mD. Representative synthetic reservoir brine was used in the tests. All plugs selected for the NMR capillary pressure study had associated porous plate data available. NMR capillary pressure curve was generated using the GIT-CAP patented methodology for three, four, and eight centrifuge speeds to understand the impact of test speed on capillary pressure curve resolution. The tests were performed at net confining stress and at ambient conditions to evaluate if large differences were observed in results. Gravimetric measurements were simultaneously obtained to ensure data quality. Two different available imaging pulse sequences – SE-SPI and the SPRITE method were also evaluated for the different samples in generating the NMR assisted capillary pressure curves. This work contributes to outlining parameters for workflow optimization when adopting this methodology in real field applications.