Abstract: According to the properties of lost circulation in the creviced formation
this paper presented a mathematical model of the lost circulation law, It is
from this mathematical model that the flow Iaw of various fluids is derived.
On the basis of the flow law, the relation between leakoff velocity or leak-
off rate and pressure difference, crevice sizes and rheological properties of
drilling fluids can be quantitatively analyzed and calculated，It is of great
guiding significance to optimizing the plugging materials of lost circulation
and reasonable plugging methods, and to improving the lost circulation
effectively in the drilling process,

Key words: Fracture Lost circulation zone Flow model Plu