Sloughing (shale) : Movement of large amounts of shale material into the wellbore, usually caused by chemical reaction or earth shift forces. Typically as clumps of particles
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}