One-way Pressure Sealant for Oilfield Drilling (F-Seal/Cleat Seal) is made from natural fiber,filling particles and additive which is a product in the form of grey yellow powder, When used in drilling, it can effectively block up leakage of every kind from the formation under the action of one-way pressure difference. It also can improve mud cake quality and reduce water loss.  It has very good compatibility and not affect the mud property. It is applicable for drilling fluids and completion fluids with a different system and different density.