| A loss of mud during drilling is known as lost circulation (LC). It may occur in permeable, fractured, or cavernous formations and may range from seepage to complete loss. Mud losses have been conventionally detected by mud pit level monitoring; however now modern techniques (delta flow kick detection, and intelligent drilling monitoring) and well logs are used. Researchers have established models which predict loss typology and allow study of loss dynamics.;Among numerous measures to minimize losses include: stress caging, casing while drilling, dual gradient drilling, aphron drilling fluids and cross-linked polymer pills. In addition to conventional lost circulation material (LCM), the industry now uses engineered pills. The LCM selection and LC evaluation techniques help the industry to organize mud loss combat. LC costs the petroleum industry hundreds of millions of dollars annually. This review provides an overview of LC and recent advances in dealing with the problem. |
