Casing 13 : Steel pipes set in wells to prevent the hole from sloughing / caving and to enable formations to be isolated (there could be several strings of casing in the well, one inside the other)
EESiFlo North America, Terminology and Glossary: Oil Well Terms, Pennsylvania, Oil: Oil Well Drilling Science and Technology, USA 2002, flowmeterdirectory.com/flowmeter_terminology, (Oil Well Drilling Sci and Tech - Amer) {555}