Every wellhead has to start somewhere, and the casing head is where it starts - the foundation spool that lands on the surface casing and carries everything above it. It suspends casing strings, seals their annuli, and anchors the whole wellhead stack. This guide explains what a casing head is, how casing hangers land in it, and how it fits under the tubing head.
Casing Head in one line: A casing head is the lowest spool of the wellhead, threaded or welded onto the top of the surface casing at ground level. It suspends the next casing string from a casing hanger, seals the annulus between casing strings, and provides a flanged base and side outlets for the rest of the wellhead stack. It is the structural and pressure-containing foundation on which casing spools, the tubing head, and the Christmas tree are built.
After surface casing is cemented in place, the casing head is installed on top of it - slip-on and welded, threaded, or flanged depending on the design and pressure rating. The next casing string run into the well (for example, the production casing) is suspended from a casing hanger that lands inside the casing head's bowl. Seals between the hanger and the head isolate the annulus between the two casing strings and contain any pressure in it.
The casing head has valved side outlets connecting to that casing annulus, letting operators monitor and bleed annular pressure. On top of the casing head, additional casing spools may be stacked for deeper casing strings, and ultimately the tubing head, so the whole wellhead grows upward from this base spool. It must therefore be rated to support the weight and pressure of everything above and the casing hung below.
The two spools are named for what they carry. The casing head carries casing - it lands on the surface casing and suspends the subsequent casing string or strings, sealing the casing annuli. The tubing head, which stacks above the casing program, carries the production tubing and seals the tubing-casing annulus. Between them, every string in the well is suspended and every annulus is sealed with its own outlets.
Together they build the wellhead from the ground up: casing head (and any intermediate casing spools) for the casing, then the tubing head for the tubing, then the tree. This layered arrangement gives each annulus - the A annulus between tubing and production casing, the B annulus outside the production casing, and so on - its own access point at the correct spool for monitoring and pressure management.
The casing head's outlets tap the outer casing annuli, and pressure in those annuli is a core well-integrity signal. Sustained casing pressure in an annulus that should be dead can indicate a casing leak, cement problems, or gas migration - conditions that regulators and operators track closely. Bleed-down and monitoring of annular pressure happens through the casing head outlets.
A cloud SCADA such as Merobix reads casing and annulus pressures from the field RTU or flow computer, so an operator can trend annular pressure at each casing string and receive an alarm if a normally dead annulus starts building pressure. The casing head provides the physical connection to the annulus; the controller and SCADA turn that connection into a continuously watched integrity indicator.
It is the lowest wellhead spool, installed on top of the surface casing at ground level. It suspends the next casing string from a casing hanger, seals the annulus between casing strings, and provides the flanged base and outlets that the rest of the wellhead - casing spools, tubing head, and Christmas tree - is built on.
The casing head is the base spool that supports the casing strings and seals the casing annuli. The tubing head stacks above it and supports the production tubing, sealing the tubing-casing annulus. The casing head handles casing; the tubing head handles tubing - each with its own hangers, seals, and outlets.
The casing head outlets tap the casing annuli, and pressure there indicates well integrity. Sustained pressure in an annulus that should be dead can signal a casing leak, cement failure, or gas migration. Operators bleed and monitor annular pressure through the casing head outlets, and regulators often require it to be tracked.
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