Incremental U-tube process to retrieve of bottom hole assembly during casing while drilling operations

摘要

A bottom hole assembly is retrieved through a casing string by lightening the density of the drilling fluid in the casing string above the bottom hole assembly to a lesser density than the drilling fluid in the casing string annulus. The bottom hole assembly moves upward in the casing string in response to an upward force created by the different densities of fluid. While moving upward, less dense fluid being displaced by the upward movement of the bottom hole assembly flows from the casing string. When the bottom hole assembly stops moving upward, slips suspended it at that intermediate point in the casing string. The operator now lightens the density of the drilling fluid in the casing string below the bottom hole assembly, again creating an upward force on the bottom hole assembly that causes the bottom hole assembly to move upward in the casing string.