Concentric Operations 2 : Well operations conducted using small diameter tubing inside conventional tubing or tubingless completions, normally with the Christmas tree in place and using a small rig or hoisting unit. (RP 57)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}