Effect of Nano ZnO on wellbore stability in shale: An experimental investigation

Abstract

Abstract Instability of shale formations is one of the major challenges during a drilling operation. Shale swelling is a time-dependent process in which water gradually infiltrates the shale structure. Due to very low permeability of shales (10−9-10−3 md) and relatively large size of solid materials of drilling mud compared to shale pore throats (3–100\u202fnm), filter cake is not capable of hindering this process. As a result, mud filtrate continuously seeps into shale, concurrently increasing pore pressure and reducing mechanical strength of the formation, where it may result in wellbore caving. One remedy to this hazard is usage of Nano-particles to block the entrance of mud filtrate into shale formations. The important factor to use of nano material in order to solve wellbore instability is the selection of practical and affordable concentration of nano particle in drilling fluid. The present research investigates the application of Nano ZnO in controlling water invasion. This Nano particle benefits size adequacy as well as suitable interfacial properties in hindering mud filtration. The impact of adding nano ZnO to reduce water seepage into shale is investigated using PPT apparatus. This test shows the increase in pore pressure in the formation due to mud filtrate invasion, hence enabling us to study the effect of different concentration of applied Nano particle on stability of shales. The results show that Nano ZnO particles, due to their size and other properties such as Hydrophilic behavior and positive charge enhance the stability of shale. Using 0.25, 0.5 and 0.75\u202fwt/volume percentage of Nano-ZnO mixture showed respectively 60%, 87%, and 96% reduction in pore pressure transmission compared to sea water sample.