Lost Returns

Downhole losses in the circulating fluid system

Lost Returns is reduction or complete absence of drilling fluid (or mud) returning to the surface through the annulus when it is pumped down the drill string. This issue occurs when the drilling fluid escapes into subsurface formations instead of circulating back to the surface and can be a cause of going underbalance and inducing a kick. Lost Returns can be caused by natural fractures in the formation, drilling through faults, porus formations or by inducing a fracture through excessive pressure.

Lost returns can be classified into different types based on severity:

Seepage Losses: A slow and steady loss of fluid, typically less than 20 barrels per hour.

Partial Losses: A more significant loss where some fluid still returns to the surface.

Total Losses: No fluid returns to the surface, which can lead to severe well control issues.

The main methods to cure losses are to reduce pump rate (reduces ECD and thus lowers the pressure on the formation) and to pump Loss Control Material (LCM) which is added to the mud system to help plug porus areas of the formation.