Fremgangsmate og apparat for okning av borekapasitet og fjerning av borkaks ved boring med kveileror

摘要

An assembly for drilling a deviated borehole includes a bottom hole assembly connected to a string of coiled tubing and includes a bit driven by a downhole motor powered by drilling fluids. A surface pump pumps the drilling fluids downhole through a cross valve to provide a first path directing drilling fluids down the coiled tubing flowbore and a second path directing drilling fluids down the annulus. The bottom hole assembly has a downhole valve allowing flow between the flowbore and the annulus. A first flow passageway directs drilling fluids down the coiled tubing flow bore and then up the annulus and a second flow passageway directs drilling fluids down the annulus and the up the flowbore. The bottom hole assembly includes a subsurface pump capable of pumping drilling fluids from the second fluid passageway to the surface. The bottom hole assembly includes an electric motor to rotate the subsurface pump and the motor is provided with power conduits embedded in a wall of the coiled tubing. Another subsurface pump may be provided, such that the subsurface pumps pump drilling fluid with cuttings to the surface and/or pump clean drilling fluids into the downhole motor to aid drilling.