Characterization of the coal pore system by resistivity and NMR methods

Abstract

ABSTRACT The development of the coal pore system is extremely significant for gas disaster prevention in coal mines and coalbed methane exploitation. To accurately, quantifiable, and non-destructively characterize the coal pore system, the relationship between total porosity, effective porosity, pore size distribution, and resistivity of coals with different degrees of metamorphic was studied by resistance test and low field NMR techniques. The dimensionless parameter ρ P that characterize the coal pore system was defined by the variety of resistivity in dry and saturated conditions. The achieved results are presented as follows: (1) The greater the ρ P (the influence of the coal pore system on the conductivity), the larger the total porosity; (2) The proportion of effective pores increased linearly with the addition of the ρ P; (3) The proportion of micropores and small pores decreased linearly as the ρ P increased, revealed that these pores had poor connectivity and complicated structure, and had a significant negative effect on the conductivity of saturated coal. (4) The proportion of mesopores and macropores gained linearly as the ρ P increased, indicated these pores had well connectivity, and had a positive influence on the conductivity. The results showed that the variety of coal resistivity from dry to the saturated condition was mainly controlled by the pore system. Therefore, a new method to characterize the coal pore system was proposed, which was exceedingly effectively, conveniently, and non-destructively.