Nuclear magnetic resonance (NMR) has been applied widely and successfully in conventional and unconventional reservoirs, and can be used to investigate petrophysical properties and fluid flow characteristics. This non-destructive, sensitive, and quick technique has been utilized in determination of pore type, porosity, pore size distribution, permeability prediction, wettability estimation, and fluid type, state and flow behavior. In this paper, the application of NMR to investigate coalbed methane and shale reservoirs is reviewed. Most of the reviewed studies are related to porosity and pore characteristics, which can be determined by analyzing the characteristics of the T2 distribution, allowing for examination of pore type and pore connectivity as well as calculation of total porosity and pore size distribution. Permeability models developed for reservoir rocks and based on porosity determined using NMR are well established and have been extended or modified to evaluate the permeability of coal or shale. Reviewed studies also include wettability investigation by comparing the subtraction of T2 distribution before and after fluid injection. Reviewed recent advances have further discussed the method of distinguishing fluid type, fluid state, and simulating fluid behavior using one-dimensional and two-dimensional NMR methods combined with changes of T2 distribution. The aim of this review is to provide readers with an overview of the capabilities of NMR and its extension to scientific research by improving the parameter optimization of the instrument and establishing the calculation method for effective surface relaxivity for coals or shales.
This research was funded by the National Natural Science Fund of China (grant nos. 41830427, 41772160 and 41922016), the National Major Research Program for Science and Technology of China (grant no. 2016ZX05043-001), the Fundamental Research Funds for the Central Universities (53200759609), and the Royal Society International Exchanges-China NSFC Joint Project (grant nos. 4161101405 and RG13991-10). Special thanks goes to Dr. Justin E. Birdwell (USGS) and Dr. Palma Jarboe (USGS) for the thorough internal review of this paper. We also thank Dr. Robert Finkelman (University of Texas at Dallas) for the constructive suggestions of this research.
- Fluid flow characteristics
- Nuclear magnetic resonance (NMR)
- Permeability prediction
- Pore properties
- Unconventional reservoir