Actuating device associated with a drill string and comprising a hydrostatic drilling fluid circuit, actuation method and application thereof

A device for actuating an equipment associated with a drill string lowered in a well, and in which a drilling fluid circulates, said circulation generating a positive differential pressure DP between the inner space and the outer space of said string wherein:

• said device comprises distribution means comprising at least two ports, one of the ports being connected through a pipe to displacement means, the other port being connected through a pipe to said inner space;
• said distribution means is adapted for controlling the communication of said drilling fluid under pressure between the inner space of the string and an inlet port for said displacement means;
• said displacement means comprise an exhaust port connected through a pipe to said outer space;
• said displacement means are adapted for being activated by converting the hydraulic energy resulting from the differential pressure DP of said drilling fluid between said inlet port and exhaust port into a mechanical activation energy and wherein the conversion is achieved directly with the co-operation of no other fluid than said drilling fluid;
• and
• wherein said distribution means comprise a position in which the pipe connecting said distribution means to said inlet port of said displacement means is closed.