Visualization of helium-water flow in tight coal by the low-field NMR imaging: An experimental observation

• Published in: Journal of petroleum science & engineering Vol. 188; p. 106862
• Main Authors: Xue, D.J., Liu, Y.T., Zhou, J., Sun, X.T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-05-2020
• Subjects: Helium-water flow; Low-field NMRI; Porosity; Saturation evolution; T2 spectrum; Visualization; Visualization; Low-field NMRI; Porosity; Helium-water flow; Saturation evolution; T2 spectrum
• ISSN: 0920-4105; 1873-4715
• DOI: 10.1016/j.petrol.2019.106862

The low-field NMR imaging (NMRI) technology plays a key role of visualization of helium-water flow in tight coal. Combined with the traditional description by T2 spectrum, the NMRI description provides an auxiliary illustration on spatial distribution of water in various pores. To distinguish the different contribution of various pores in helium-water flow, a flow function-based classification of adsorption pore (AP), percolation pore (PP) and migration pore (MP) are suggested. It depends on the periodic appearance of peak and valley of the T2 spectrum. Although all pores contribute to porosity, the unchanged AP peak of T2 spectrum and the trapped water in 2D distribution shows AP contributes little to the helium-water flow. Further, the saturation evolution is clearly illustrated by CPMG sequence and NMRI visualization. Both descriptions show a strong dependence of saturation evolution on pore size distribution. Finally, the porosity is modified based on the squeezing effect of enhancing the peak of T2 spectrum. The experimental result shows the helium-water flow is properly demonstrated by the low-field NMRI method, but the drainage efficiency of helium displacing water is not high due to the trapped water in AP.
•Visualization of helium-water flow in tight coal by the low-field NMRI.•Saturation evolution visualised by the low-field NMRI.•Pore classification of AP, PP and MP for the helium-water flow.•Modification of T2 spectrum and porosity by the confining pressure.