Wellhead Christmas Tree

Overview

A wellhead christmas tree is the stack of valves, spools and fittings bolted to the top of a producing oil or gas well. It sits on the tubing head and controls every fluid path in and out of the well: production to the flowline, fluid injection for kill or chemical service, and vertical access for wireline and coiled-tubing intervention. The name comes from the branching silhouette of the valve stack. The tree is the surface end of the well's pressure-containment system, so each component is rated and certified to API 6A for the well's maximum shut-in pressure.

A conventional vertical tree routes well flow up a single central bore. Stacked gate valves in that bore form the safety barriers; horizontal wing outlets take production off to the choke and flowline.

How it works

Produced fluid rises through the Tubing Head & Spool, which lands and seals the tubing hanger so the tubing string and the casing annulus stay isolated. Flow then passes the Master Gate Valve gate valves, the lower master is the manual barrier and the upper is a hydraulic fail-safe-close valve that shuts the well automatically if control pressure is lost.

Above the masters, the Flow Cross / Tee splits the vertical bore to the horizontal Wing Valve outlets. The production wing feeds the Adjustable Choke, whose adjustable bean and carbide trim drop pressure and set the flow rate; the kill wing allows fluid to be pumped back in. The Swab Valve caps the top of the bore and opens to give straight vertical access for wireline tools and coiled tubing through a lubricator.

Every actuated valve is driven from the Control Panel, a hydraulic unit whose solenoids and accumulators hold the gates open and bleed down to close them on demand. Operators read tubing and casing pressure from the Pressure Gauge sets, and all spools join through the Flange & Gasket Set of studded API flanges sealed by metal ring-joint gaskets.