The wellhead is a stack of spools, and the tubing head is the one that carries the production tubing. It sits high in the stack, suspends the tubing string, seals off the space around it, and gives access to that space. This guide explains what a tubing head is, how the tubing hanger lands in it, and how it differs from the casing head below it.
Tubing Head in one line: A tubing head is a wellhead spool that supports the production tubing string, seals the annular space between the tubing and the production casing, and provides monitored access to that annulus. The tubing string hangs from a tubing hanger that lands and seals inside the tubing head. It sits above the casing head in the wellhead stack and below the Christmas tree, forming the transition from the casing program to the tubing and tree.
The tubing head is a flanged spool bolted onto the top casing head or casing spool below it. The production tubing is run in the hole and then suspended by a tubing hanger - a machined component that lands in a prepared bowl inside the tubing head. The hanger's seals isolate the tubing bore from the annulus around it, so that produced fluid stays inside the tubing while the annular space is sealed off and controlled.
The tubing head has side outlets that connect to the tubing annulus - the space between the tubing and the innermost casing. These outlets, fitted with valves, let operators monitor annulus pressure, bleed it down, or inject into it (for example, chemical injection or gas for gas lift). Above the tubing head sits the Christmas tree, which controls flow from the tubing itself.
The wellhead stack is built from the ground up. The casing head is the lowest spool, landing on the surface casing and supporting the casing strings. Intermediate casing spools may stack above it. The tubing head is the last spool before the tree, and it is specifically for the tubing string, not casing. So the casing head handles the casing program and the tubing head handles the tubing string - each with its own hangers, seals, and annulus outlets.
This layering means every annulus in the well has a corresponding set of outlets at the appropriate spool, giving operators a way to monitor and manage the pressure in each annular space independently. The tubing head governs the innermost annulus, the one most directly tied to production and to lift methods like gas lift or chemical injection.
The tubing head's annulus outlets are a key monitoring point. Tubing-casing annulus pressure is a direct indicator of well integrity and lift behavior - a rising annulus pressure can flag a tubing leak, a packer problem, or gas migration, and gas lift and injection wells manage annulus pressure deliberately. A pressure transmitter on the annulus outlet turns that pressure into a signal the field controller reads.
A cloud SCADA such as Merobix reads the wellhead and annulus pressures from the RTU or flow computer over Modbus, DNP3, or OPC UA, so an operator can watch tubing-head annulus pressure alongside tubing pressure from a browser. The tubing head provides the physical tap into the annulus; the controller and SCADA turn its pressure into a continuously monitored, alarmable value.
The casing head is the lowest wellhead spool and supports the casing strings; the tubing head sits above it and supports the production tubing. The tubing head suspends the tubing hanger, seals the tubing-casing annulus, and provides outlets to that annulus, while the casing head handles the casing program.
A tubing hanger is the machined component that lands and seals inside the tubing head to suspend the production tubing string. Its seals isolate the tubing bore from the surrounding annulus, so produced fluid stays in the tubing while the annular space is sealed and controlled through the tubing head outlets.
The side outlets connect to the tubing-casing annulus. Valved outlets let operators monitor annulus pressure, bleed it down, or inject chemicals or gas lift gas. Annulus pressure at the tubing head is an important indicator of well integrity, so these outlets double as a monitoring point.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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