Gas transport in dominantly microporous rocks such as coal, shale is significantly controlled by Klinkenberg or slippage effect at low reservoir pressures. Pore size fractions of the concerned reservoir rock control the degree of Klingenberg effect. This study tries to assess the differences in Klinkenberg effect in dissimilar coals owing to their difference in pore-size distributions. We report apparent permeabilities of three Gondowana coal samples from the Bokaro, Jharia, and Bansgara coalfields at room temperature and constant isostatic stress (6.2 MPa). The linear plots of apparent permeability versus inverse pore pressure were modelled using the Klinkenberg equation, and non-linear plots by the Ashrafi equation to determine the slippage coefficient and intrinsic permeabilities. Ashrafi model reports lower values of slippage corrected permeability compared to the Klinkenberg model. The slippage coefficient and intrinsic permeability obtained from N2 and CO2 is different for the Bansgara sample. The trends between transport parameters and pore-size parameters were examined. The slippage coefficient decreased with interconnected porosity and total specific pore volume. Intrinsic permeabilities showed an opposite trend to that of the slippage coefficient. The Bansgara sample having larger volumetric proportion of micropores in the pore volume gamut with open ended interconnected pore network resulted in the lowest slippage coefficient and highest intrinsic permeabiliity. Reporting the slippage coefficients and intrinsic permeabilities with corresponding pore size distributions of coal samples from different global basins will lead to statistically significant empirical relationships between pore size parameters and slippage coefficients.

The microstructures, textures and seismic anisotropy of a foliated blueschist-eclogite rock from Naga Hills Ophiolite (NHO) complex, North-East India has been investigated to understand the fabric relationship and deformation mechanism prevailed during the metamorphism and subduction of the Neo-Tethys oceanic crust. The Naga Hills blueschist-eclogite rock essentially contains omphacite, phengite, glaucophane, and garnet, representing an oceanic crust that experienced P-T stability field of blueschist and further eclogite metamorphism before it resurfaced accreting in the Naga Hills. Omphacite and glaucophane show weak shape preferred orientation (SPO), while phengite displays a strong SPO. The Crystallographic Preferred Orientations (CPO) of omphacite is characterized by the [001]-axes gridles within the foliation, and the (010)-poles concentrated sub-perpendicular to the foliation. For glaucophanes, the [001] axis aligns parallel to lineation and the [100] axis and (110) pole plunge perpendicular to foliation. These CPOs correspond to SL-type fabrics, related to a deformation geometry within the plain strain field and they developed from plastic deformation through dislocation creep. The seismic anisotropies of the individual minerals, blueschist-eclogite domains and their contributions in the bulk rock anisotropy has been discussed. The calculated seismic anisotropies (AVP and AVS) of bulk rock are 12.8% and 8.1%, respectively. This strong seismic anisotropy is due to the presence of phengite and glaucophane and can contribute to the observed seismic anisotropy in the subduction zone. The average low P-wave velocity of whole rock from NHO compared to blueschist is probably due to the low P-wave velocity of phengite (avg VP: 6.2 kms-1). Therefore, the low seismic velocity in the upper layer and the strong seismic anisotropy of the subducting oceanic crust can be attributed to the presence of glaucophane and phengite.