Characteristics of movable fluid and pore size distribution of low rank coals reservoir in southern margin of Junggar basin

To analyze the movable fluid, bound fluid and pore size distribution of low rank coal reservoir in southern margin of Junggar basin, the paper performed the high-speed centrifuge and low-field nuclear magnetic resonance experiment on six coal samples from six coalfields in southern margin of Junggar basin. The experimental results showed that low rank coal mainly developed adsorption pores, followed by seepage pore and fracture. The optimum centrifugal pressure for establishing irreducible water state is 1.380 MPa. The paper integrated the T₂ spectra of both saturated water state and irreducible water state to calculate movable fluid porosity and residual water porosity. The movable fluid porosity ranges between 0.45%~1.89%(averaging at 1.29%), the residual water saturation ranges between 1.03%~7.45%(averaging at 4.18%). The movable fluid porosity shows exponential relationship with air permeability (R²=0.935 8). Based on the method of "centrifugal-T_2C", the pore size of low rank coal in southern margin of Junggar basin was mainly distributed in 0.01~1 μm and the average of pore size is 1.771 μm.