Review of Recent Developments in NMR Core Analysis

Abstract

The last 10 years have witnessed numerous new developments and advancements in nuclear magnetic resonance (NMR) rock core analysis both in conventional and unconventional reservoirs. On the hardware side, NMR instruments are now capable of handling hundreds of thousands of radio frequency (RF) pulses, and the pulses can be more closely spaced than ever. This allows measuring samples with very fast relaxation times, which was not possible before. Higher field NMR spectrometers operating at frequencies of ~12 MHz and ~20 MHz (in addition to the standard low-field ~2 MHz instruments) were introduced, which drastically improved the signal-to-noise ratio (SNR) and even allowed two-dimensional (2D) and three-dimensional (3D) NMR imaging to be performed on the samples to complement traditional relaxation measurements. Another consequence of using higher field instruments is that even samples with a very low amount of NMR signal can now provide useful data in a reasonable amount of time. Additional hardware improvements include the development of NMR-compatible high-temperature and high-pressure vessels and faster and more robust electronics and computers, which allow faster data acquisition, processing, and a more user-friendly environment for new NMR pulse sequence design and implementation. Following the hardware improvements, new applications were developed for rock core analysis, including modified Carl-Purcell-Meiboom-Gill (CPMG) pulse sequences for minimizing sample heating. NMR-based wettability, relative permeability, capillary pressure, cuttings, and long core measurements have also been successful. In unconventionals, NMR-based gas isotherm measurements and fluid-typing measurements are now common practices. This review paper sets out to summarize the recent NMR developments in the industry as well as provide references where more details can be found on each topic.