Patent ID: 9493986
Filing Date: 2016-11-15
CPC Classification: E21B

Claim Text:
1. A method for initiating gas injection into a borehole in a managed pressure drilling process during a drilling procedure, wherein a drillstring extends from a location at an Earth surface down into the borehole, the drillstring comprises a drill bit at an end distal from the Earth surface, a gas injector is in fluid communication with an annulus surrounding the drillstring and the fluid communication between the gas injector and the annulus is provided by one or more orifices at a depth below the Earth surface, the method comprising: pumping a volume of gas into the gas injector to charge the gas injector to a charging pressure at which the volume of gas within the gas injector extends down towards the one or more orifices; pumping a quantity of gas down the drillstring through the drill bit and into the annulus, wherein this quantity of gas is sufficient to produce a train of gas in the annulus extending upwardly from the one or more orifices and thereby lower pressure at the one or more orifices so that gas charged within the gas injector expands and flows through the one or more orifices into the annulus; and pumping further gas through the gas injector into the annulus at a specific flow rate to maintain the train of gas in the annulus extending from the one or more orifices to the Earth surface and produce a desired bottomhole pressure in the borehole.