When drilling a well in a formation, loss of return fluid is experienced due to leaking of drilling fluid into fractures or weak formation surrounding the well. This may result in a loss of well control as drilling fluid is a barrier towards the formation. This is conventionally addressed by firstly pumping Lost Circulation Material (LCM) to seal the fractures, or secondly to cement and loose the section. The pressure in a well increases with depth, and the combined static and dynamic pressure from the drilling fluid, which is the Equivalent Circulating Density (ECD), needs to be higher than the pore pressure of the formation to maintain control. However, the pressure from the drilling fluid needs to be lower than the formation strength pressure to avoid the formation of fractures through which drilling fluid can leak out. In wells there can be intervals with a relatively narrow window between pore pressure and formation strength, and where the risk of lost circulation is higher.
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