Gas injection for managed pressure drilling

摘要

Injection of gas into a managed pressure drilling system to provide for operation of the drilling system in a pressure window defined by the pore pressure of a formation being drilled and a fracture pressure of the formation. The gas is injected through gas injection ports and drilling fluids are allowed to flow between the drilling annulus and the gas injection system though a plurality of flow ports that are disposed vertically below the gas injection ports in the borehole being drilled. The gas injection ports and the flow ports are configured so that when gas is flowing through the gas injection ports, the flow ports are sealed.

主权项

1. A method for injecting gas into a drilling annulus surrounding a drillstring during a drilling process for drilling a borehole into a subterranean formation, where the drilling annulus comprises an annular space between the drillstring string and a casing string and the drillstring extends from a surface location down the borehole, the method comprising:
pumping gas into the drilling annulus, wherein the gas is pumped into an injection pipe and through a set of one or more gas injection ports into the drilling annulus, and wherein the set of one or more gas injection ports are in fluid communication with the gas injection pipe and the drilling annulus; flowing drilling fluids between the drilling annulus and the gas injection pipe through a set of one or more flow ports, wherein the set of one or more flow ports are in fluid communication with the gas injection pipe and the drilling annulus, and wherein the set of one or more flow ports are a vertical distance below the set of one or more gas injection ports such that the set of gas injection ports are located between the set of one or more flow ports and the surface location; and using a hydrostatic head of a column of drilling fluids extending between the set of one or more flow ports and the set of one or more gas injection ports to seal the set of one or more flow ports when gas is flowing from the drilling pipe through the set of one or more gas injection ports into the drilling annulus.