Concentric Completion : A multiple completion in which the upper zone flows to the surface through the annulus formed by the casing and the deeper zone tubing. Usually used only in sweet, dry gas upper completions
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}