Impact of Surface Roughness and Liquid Salinity on Shale Wettability

This study explores the effect of surface roughness and liquid salinity on the wettability of shale. Varying levels of surface roughness are imparted onto the shale samples using sandpapers with differing grits and polishing disks. An optical profiler is also applied to determine the surface roughness and create 3D tomography models for each shale sample. Furthermore, contact angle tests were conducted using liquids with different salinity levels to determine the effect of salinity to surface wettability. The results indicate a marked increase in contact angle with decreasing surface roughness. This suggests that a smoother surface can considerably mitigate water-lock effects and reduce water flow resistance within the shale. Additionally, the results obtained from utilizing liquids with varying salinity demonstrate that higher salinity levels lead to lower shale contact angles. Moreover, the salinity effect is more pronounced on smoother surface than on a rougher one. A power function was found to aptly describe the mathematical relationship between the arithmetic average of surface roughness (Ra) and contact angle, validated by a high R² value of 0.863. The implications of these findings are significant for hydraulic fracturing and gas production strategies, as they can provide more reliable guidance for selecting operational parameters.