Patent ID: 9422784
Filing Date: 2016-08-23
CPC Classification: E21B

Claim Text:
1. A snubbing apparatus for a wellbore having a wellhead, an elongate string being inserted into the wellbore through the wellhead, the snubbing apparatus comprising: a snubbing stack having an upper sealing element and a lower sealing element, wherein, in operation, the upper and lower sealing elements seal between the elongate string and the snubbing stack, the lower sealing element sealing the snubbing stack against a wellbore pressure below the lower sealing element; a string driver carried by the snubbing stack, the string driver manipulating the elongate string through the upper sealing element and the lower sealing element; a source of inert liquid connected to supply inert liquid to the snubbing stack between the upper sealing element and the lower sealing element; and a pressure sensor connected to sense the wellbore pressure below the lower sealing element and connected to provide a pressure signal to the source of inert liquid, the source of inert liquid being configured to pressurize the inert liquid in the snubbing stack between the upper sealing element and the lower sealing element in response to the pressure signal.