ASSEMBLY FOR PRESSURE CONTROL WHEN DRILLING AND METHOD TO CONTROL PRESSURE WHEN DRILLING IN A FORMATION WITH UNPREDICTABLE HIGH FORMATION PRESSURE

摘要

Assembly for pressure control when drilling underground to locate or produce hydrocarbons; whereby the drilling is done by means of a drill string with fluid circulation down through the drill string and up through an annulus between the drill string and the open hole or casing, as the underground in the open hole may comprise one or both of: areas with formation strength which is unable to withstand the pressure from the fluid circulation without fracturing and areas with formation pressure which cannot be combined with each other or the fluid circulation pressure without the fluid unintentionally leaking in or out from the above-mentioned areas. The assembly is distinguished in that onto the drill string a bottomhole assembly is fitted, comprising: a reversible and expandable packer fitted near to the lower end of the drill string to seal the annulus, controllable from the surface a measuring device for measuring the pressure inside the annulus both above and below the packer, with means to simultaneously transfer the data to the surface, a circulation valve fitted above the packer and controllable from the surface in order to open or close off the communication of fluids between the inside of the drill string and the annulus, a control valve (closing valve) fitted below the circulation valve and controllable from the surface, to open and close off the communication of fluids through the drill string, and a connecting sub located above the packer and controllable from the surface for connecting and un-connecting the drill string.