عنوان مقاله [English]
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 (10-6 - 10-12 D) and relatively large size of solid materials of drilling mud compared to shale pore throats (3-100 nm), 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 the use of Nano-materials to block the entrance of mud filtrate into shale formations. Using nano-particle additives is one of the methods to reduce the entrance of mud filtrate into the shale formations. The present research investigates the application of Nano ZnO in controlling shale swelling. This nano particle benefits size adequacy as well as suitable interfacial properties in controlling 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 additives on stability of shales. The results show that Nano ZnO particles reduces shale’s wettability effectively, and thereby reducing water penetration, due to their sizes and other chemo-physical properties; such as, specific surface area, electric charge. Using 0.25, 0.5 and 0.75 weight/volume percentage of Nano-ZnO mixture shows respectively %60 ,%87, and %96 reduction in pore pressure transmission compared to a sea water sample.