CIRCULATION SYSTEM TO RAISE DRILL STRING ASSEMBLY BOTTOM IN PROCESS OF DRILLING ON CASING STRING Russian patent published in 2013 - IPC E21B23/08 E21B10/66 

FIELD: mining.

SUBSTANCE: in process of drilling on a casing string the drilling mud is pumped via a discharge pipeline leading into a channel in the grip of the casing string and downwards along the casing string. The drill string assembly is installed on the lower end of the casing string for drilling of the well bore. The drill string assembly bottom is raised by installation of the circulation sub with a side outlet hole in the casing string below the grip of the casing string. The return flow line is used to connect the outlet hole with the circulation system. The operator supplies fluid medium downwards along the circular space behind the casing string and back upwards along the casing string, providing for upward movement of the drilling string assembly bottom. The fluid medium passing back upwards along the casing string is drained via the outlet hole in the circulating sub into the circulation system without passing through the channel in the grip of the casing string.

EFFECT: increased efficiency of raising a drilling string assembly bottom.

20 cl, 14 dwg