Si trova su / Altri legami
© 2021 American Chemical Society.We report apparent permeabilities (ka) of coal samples from Bansgara, Jharia, and Bokaro collieries from Gondwana coalfield (India) to assess the Klinkenberg coefficients (b) and intrinsic permeabilities (k∞) owing to their characteristic pore–size distributions. All ka values were measured with N2 at room temperature, constant 6.2 MPa effective stress, and up to 7.6 MPa pore pressures (Pp), except for the Bokaro samples (maximum 3.5 MPa Pp). The permeabilities of the Bansgara samples were also measured with CO2 up to Pp 3.5 MPa. The pore–size distributions were measured using low–pressure N2 adsorption–desorption. We determined the b and k∞ from the plots of ka versus (1/Pp). The linear and nonlinear sections of ka versus (1/Pp) plots are modeled using the Klinkenberg and Ashrafi equations, respectively. The Ashrafi model yields lower k∞ over the Klinkenberg model. The k∞ and b of the Bansgara sample determined from the Klinkenberg model are nonidentical for N2 (0.073 md and 0.33 MPa) and CO2 (0.0052 md and 7.27 MPa). Our data show that b decreases with the total pore volume and interconnected porosity, whereas k∞ increases with the total pore volume and interconnected porosity. The Bansgara sample with open–ended and well–connected micropores has the lowest b. The Jharia and Bokaro samples have volumetrically higher mesopores; although the pores are semiopen–ended with poor connectivity, they result in higher b compared to the Bansgara sample. The results of this study suggest that gas permeability evolution due to slippage effect is a strong function of the pore characteristics of the concerned reservoir.
