CONTROLLING BACKFLOW PRESSURE DURING RETRIEVAL OF BOTTOM HOLE ASSEMBLY

摘要

A bottom hole assembly in a casing-while-dr tilingoperation is retrieved by displacing the fluid in the casing string with alessdense fluid than the fluid in the annulus. The bottom hole assembly movesupward in the casing string in response to an upward force due to thedifferent densities of fluid in the casing string and in the annulus.Displacedfluid flows out of the casing string and through a restrictive orifice of achoke. The flow area of the orifice is varied as the bottom hole assemblymoves upward to control the rate at which the bottom hole assemblymoves upward.