Gate valves are used throughout the drilling phase to provide access to the annulus, and throughout completion and production phases to open or close the well bore.
Wellhead and Christmas Tree
A wellhead is the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment.
A wellhead must be present to utilize a Christmas tree and is used without a Christmas tree during drilling operations. The wellhead is the component at the surface of a well that provides the structural and pressure-containing interface for the drilling and production equipment. Producing surface wells that require pumps (pump jacks, nodding donkeys, etc.) frequently do not use any tree because no pressure containment is required
Oil well Christmas Tree is an assembly of valves, spools, and fittings used for an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well, and other types of wells. It is named for its resemblance to a decorate tree at Christmas. The primary purpose of a wellhead is to provide the suspension point and pressure seals for the casing strings that run from the bottom of the hole sections to the surface pressure control equipment.
While drilling the oil well, surface pressure control is provided by a blowout preventer (BOP). If the pressure is not contained during drilling operations by the column of drilling fluid, casings, wellhead, and BOP, a well blowout could occur when the well has been drilled, it is completed to provide an interface with the reservoir rock and a tubular conduit for the well fluids. The surface pressure control is provided by a Christmas tree, which is installed on top of the wellhead, with isolation valves and choke equipment to control the flow of well fluids during production.
Wellheads are typically welded onto the first string of casing, which has been cemented in place during drilling operations, to form an integral structure of the well. In exploration wells that are later abandoned, the wellhead may be recovered for refurbishment and re-use.
The Christmas tree and the wellhead work together to bring oil and gas to the surface.