A mud loss treatment drilling tool includes the tool having an upper tooljoint to a lower end of an above drill pipe string, one or more tanks with a through channel for a drilling fluid flow, a lower tooljoint connected to a BHA assembly at least comprising a drill bit; the tank arranged for holding a swellable sealant agent; the swellable sealant agent arranged for mixing with water to swell; the tank provided with an outlet to the through channel for the swellable sealant agent, so as for, when an undesired mud loss is detected, for flushing all or part of the swellable sealant agent into the through channel, so as for a mixture of the swellable agent and the water to start reacting to swell during the time it takes the mixture to reach a fracture extending from a well under drilling by said BHA, so as for continuing to swell and block the fracture to stop the undesired mud loss.