Low-field NMR Ecological Research on the Effects of Confining Pressure Changes on Pore Fissure Characteristics of High-rank Coal

Ecologically, the pore fissure system of a coal reservoir is the accumulation place and migration channel of coalbed methane. Pore fissure distribution and environmental characteristics play important roles in enrichment and osmosis migration of coalbed methane. Surrounding stress of coal reservoir is important to internal pore fissure system development in environment. The ecological variation law of pore fissure characteristics of coal samples with and without 1–9 MPa of confining pressure was analyzed through low-field nuclear magnetic resonance experiments to reveal the influence of confining pressure changes on pore fissure characteristics of high-rank coal. Results demonstrated that with the increase of confining pressure, pore volume in coal samples decreases and pore size distribution changes. A few small pores will be converted into large pores, and porosity gradually decreases in the power function form. The proportion of small pores increases, whereas those of middle and large pores decrease. The internal pore connectivity of ecological coal samples is enhanced accompanied with different variation trends of permeability. Corresponding environmental causes were further analyzed.