Definition - What does Hydril Thread mean?
A Hydril Thread is a premium thread design which connects a hydril with a wellbore for shut in purposes. A hydril is a specialized valve which is used to prevent blowout while monitoring or sealing oil and gas wells. It is one of the types of blowout preventers (BOP's). The annular blowout preventer is known as hydril, which is named after one of the manufacturers of the device. To shut in the wellbore the hydril uses the principle of wedging on which the hydril threads are made to make a joint.
Petropedia explains Hydril Thread
In onshore or offshore wellhead platforms, the flow of hydrocarbons from the drilled wellbore is controlled with the help of the wedge-faced piston used by the hydril annular blowout preventer. The key advantage of these annular preventers is that they can seal a variety of wellbore and pipe sizes. At the top of a BOP stack there is always one hydril annular blowout preventer. For the open holes, elastomeric sealing doughnuts are required. This is why they are considered as not so reliable for sealing an open hole in tubular (or around tubular). The doughnuts used with the hydril are according to the API specification. These BOP’s are controlled by acoustical control signal, deadman switch, ROV intervention or electrically.