Patent ID: 11346173

Abstract:
There is disclosed a milling apparatus (2) having a use in milling a window (88) in downhole tubing (1) located in a borehole (32) of a well. The milling apparatus comprises a main body (22) comprising an internal bore (42) defining a flow path through the body; a mill head (20) having at least one flow port (29); an internal chamber (15) which can contain a fluid, the internal bore of the main body defining at least part of the chamber; first (16) and second (23) seal assemblies disposed within the internal bore; and a communication port (17) located upstream of the second seal assembly. The seal assemblies are initially sealed relative to the main body, so that fluid communication along the internal bore past the seal assemblies is restricted and fluid contained in the chamber isolated from fluid external to the chamber. At least part (11) of the first seal assembly is translatable within the internal bore in a direction towards the second seal assembly, to transmit fluid contained in the chamber through the communication port to a fluid operated device (5) associated with the milling apparatus, to operate the device. At least part (24) of the second seal assembly is translatable within the internal bore from a closed position (FIG. 4) in which said part is in sealing contact with the main body so that said flow port is out of communication with the chamber, to an open position (FIG. 8) in which said part is out of sealing contact with the main body so that fluid can flow along the internal bore past the second seal assembly and so out of the apparatus through said flow port.