1. Types
(1) By Number of Suspended Casing Strings:
- Single-stage : Generally used in low-pressure, shallow production wells
- Two-stage: Suitable for most areas with well-defined formation pressures; widely used
- Three-stage: Typically used in high-pressure deep wells or exploratory wells
(2) By Casing Hanger Structure:
- Slip-type
- Mandrel-type (threaded)
- Integral (welded) casing head
(3) By Body Connection Method:
- Flanged
- Clamp-type
- Independent threaded type (casing head with threaded connections between the top of the casing string and the bottom of the tubing head)
(4) By Body Structure:
- Single-body (one hanger per body)
- Composite (multiple hangers in one body)
2. Structure and Sealing of Casing heads
(1) Components:
(2) Rubber Seal Working Principle:
The casing head seal consists of body, BT-type rubber seal ring, casing hanger, dovetail rubber seal ring, lockdown screw V-seal, and sealing gasket. The casing hanger seats on the its body shoulder, creating a rigid passive seal through metal-to-metal contact due to casing weight. The seal between the casing hanger and casing is a threaded seal.
The casing head cross has BT seals matching the casing hanger (or casing) outer diameter, with corresponding grease injection and test ports. High-pressure sealant must be injected through the grease valve for the BT seal to function. If leakage occurs, inject sealant through both the grease valve and test valve. Injection pressure should not exceed the flange's rated working pressure or the casing's rated collapse pressure for casing seals.
Its cross-side outlet flanges connect to gate valves (or blind flanges), threaded flanges, connectors, check valves, and pressure gauges to monitor annular pressure between casing strings.
(3) Metal and Rubber Sealing:
The metal and rubber seal assembly includes the body, BT-type rubber seal ring, upper metal seal component, lower metal seal component, casing hanger, dovetail rubber seal ring, lockdown screw V-seal, and sealing gasket.
The lower metal seal component's sealing principle relies on the design of the metal seal ring, cross, and casing hanger. The geometric dimensions of the components ensure that when the 45 degree tapered surface of the lockdown screw rotates, it forces the lower metal seal component's pressure ring downward, deforming the U-shaped ring of the metal seal ring assembly to seal the casing hanger.
