Yousef Soleymani - Petroleum University of Technology

Lost circulation or lost return is defined as the partial or total loss of whole drilling fluid to subsurface formations. Probably the most problematic situation is naturally fractured formations where the operator may face total loss with no mud return in the annular. The voids or large fractures encountered in this case are often too large to be plugged with conventional Lost Circulation Materials (LCM). Hence, massive lost circulation is a major and costly drilling problem. New approaches to cure extreme losses are “settable plugs”. This term is used for slurries which gel or solidify in seal zones. When these fluids are being lost to the formation they should gel quickly as it travels away from the wellbore, as the fluid velocity decreases. Some examples of such plugging products are gunks or cross-linked polymers. The objective of this paper is to explain extreme lost circulation problem and introduce different solutions in addition to recently developed materials to cure or mitigate this problem. And finally, the application of a polymer based wellplug is studied in one well of the Varavi Gas Field (National Iranian Central Oil Field Company) and the reasons of unsuccessful trial of this material with regard to future recommendations are examined.