Detailed Pore Structure Study of Damodar Valley and Upper Assam Basin Shales Using Fractal Analysis
Venkata Yasaswy Turlapati, B.K. Prusty, Tuli Bakshi
Abstract
Pore characteristics heavily influence the gas storage mechanisms in gas shales. For a deep understanding of the pore structure characteristics, the fractal analysis was performed through low-pressure nitrogen (N2) adsorption experiments on 5 shale samples collected from Gondwana and Assam basins of India. The characteristics of low-pressure N2 adsorption isotherms revealed the mesoporous nature of the shale samples. It can be observed that N2 adsorption was dominated by van der Waals forces until the relative pressure (P/Po) reached ≈0.45, and later, it was dominated by surface tension thereby dividing the adsorption curve into 2 regions at P/Po ≈ 0.45. Fractal dimensions (D) were estimated using the Frenkel–Hasley–Hill (FHH) method in the above-mentioned 2 regions separately. The fractal dimensions were further correlated with the shale constituents and different pore characteristic parameters. Results indicate that fractal dimensions are positively correlated with the BET specific surface area (BET-SSA) and quartz content. However, fractal dimensions negatively correlated with the TOC, CO2 micropore volume, and average pore diameter. Comparison of the fractal dimensions with the shale pore characteristics suggested that the selected shale samples are highly nonhomogeneous and are dominant with complex micropores and mesopores.