Drilling fluids for drilling in shale and clay rocks.
Rafał Wiśniowski, Małgorzata Uliasz, Grzegorz Zima, Sławomir Wysocki, Magdalena Gaczoł
Vol. 32, no. 2 (2015), s. 415-428, 
Clay shale rocks large intervals drilling generates a serious issues caused by hydration, swelling and dispersion of clay rock. Those reactions might lead to break-downs and complications in drilling as the consequences of borehole wall stability loss that have source in cave effect (occurrence of caverns and cavings) and borehole diameter sharp decreasing. Therefore, the outcomes of the research that have been undertaken are muds formulas adjusted for drilling various clay rock intervals.