Insights into moisture content in coals of different ranks by low field nuclear resonance

Abstract

The moisture occurrence in coal reservoirs has important significance in the evaluation of gas-bearing properties and production of coalbed methane (CBM). In order to investigate the occurrence mechanism of moisture content of coals, a series of experiments including mercury intrusion porosimetry (MIP), low temperature nitrogen gas absorption/desorption (N2GA) and nuclear magnetic resonance (NMR) are conducted in this study to characterize and quantify pore structure properties. The nature of occurrence of moisture content in coal reservoir pores is then divided into four categories by NMR saturation and centrifugation experiments. The bound water content in the adsorption pore accounts for the highest proportion. Based on the relevance of bound water content and its influencing factors, moisture occurrence in coal reservoirs of different ranks is revealed by SPSS statistical methods. The moisture content of low-rank coal is mainly controlled by elemental oxygen and specific surface area, whereas for medium- and high-rank coals, this is controlled mainly by minerals. Our study finds application in CBM evaluation and development.

Keywords

• Pore structure
• Moisture content
• Nuclear magnetic resonance
• Occurrence mechanism