Surface Wellhead Systems, Christmas Trees & Downhole Completion Tools
Wellhead and downhole equipment forms the pressure-containing and flow-controlling infrastructure from the subsurface reservoir to the surface production facility. Unlike individual valves—which are components within these systems—this category covers the integrated assemblies, structural components, and specialized downhole tools that enable safe drilling, completion, and production operations.
Hoger supplies API 6A wellhead systems, API 11D1 downhole completion tools, and associated accessories from qualified global manufacturers. Every assembly comes with full material traceability, pressure test certification, and compliance documentation.
Category Structure at a Glance
| Category | Primary Function | Key Products |
|---|---|---|
| Wellhead Systems & Components | Surface pressure containment and casing/tubing suspension | Casing heads, tubing heads, casing spools, hangers |
| Christmas Tree Assemblies | Surface flow control and well access | Vertical trees, horizontal trees, tree components |
| Completion Tools | Downhole zonal isolation and flow management | Packers, bridge plugs, sliding sleeves, landing nipples |
| Liner Hangers & Accessories | Casing suspension in the wellbore | Mechanical and hydraulic liner hangers |
| Downhole Flow Control | Subsurface safety and flow regulation | SSSVs, downhole chokes |
| Wellhead Accessories | Sealing, protection, and installation tools | RTJ gaskets, stud bolts, wear bushings, test plugs |
1. Wellhead Systems & Components
The wellhead is the structural and pressure-containing interface between the subsurface casing strings and the surface production equipment. It suspends casing and tubing weight, isolates annuli, and provides a foundation for the BOP during drilling and the Christmas tree during production.
1.1 Casing Heads & Housing
The lowermost component of the wellhead assembly. Supports the surface casing string and provides a landing shoulder for the next casing hanger.
- Standard: API 6A
- Configurations: Slip-on weld, threaded, or flanged bottom connection
- Outlet Options: Studded or flanged side outlets for annulus access
- Material Classes: AA to HH per API 6A (dependent on sour service requirement)
- Pressure Ratings: 2,000 to 20,000 psi
1.2 Casing Spools
Intermediate wellhead sections that support additional casing strings. Each spool provides a landing shoulder for a casing hanger and side outlets for annulus monitoring or gas lift injection.
- Standard: API 6A
- Configurations: Straight bore or tapered bore
- Side Outlets: Typically two (180° opposed) for annulus access
- Bottom/ Top Connections: Studded or flanged to match adjacent components
1.3 Tubing Heads & Spools
The uppermost wellhead spool. Supports the tubing hanger and provides the interface for the Christmas tree.
- Standard: API 6A
- Tubing Hanger Profile: Matches tubing hanger type (mandrel or slip-type)
- Side Outlets: For tubing-casing annulus access
- Lockdown Screws: Mechanically secure tubing hanger (optional for some designs)
1.4 Tubing Hangers
Suspends the tubing string within the tubing head. Seals the tubing-casing annulus from the wellbore and surface.
- Types:
- Mandrel Tubing Hanger: Solid body, seals around OD. Most common.
- Slip & Seal Tubing Hanger: Slips grip casing ID, seals compress to isolate. Used where tubing tension must be controlled.
- Material Classes: Per API 6A, matched to wellhead material class
- Seal Types: Elastomeric (standard), PTFE, or metal-to-metal (for HPHT/sour)
1.5 Adapter Flanges & Crossovers
Connect wellhead components of different sizes, pressure ratings, or connection types.
- Standard: API 6A
- Types: Crossover flanges, spacer spools, double-studded adapters
- Service: Pressure and structural transition between BOP and wellhead or tree and wellhead
2. Christmas Tree Assemblies
The Christmas tree (Xmas tree) is the assembly of valves, spools, and fittings installed on top of the wellhead to control production flow. It provides the flow path for hydrocarbons, well access for intervention, and annulus monitoring.
2.1 Conventional (Vertical) Trees
The master valve and flow path are oriented vertically above the tubing head. Flow exits through a side outlet (wing valve).
- Standard: API 6A
- Configuration: Master valve (lower + upper), swab/crown valve, wing valve(s)
- Typical Components:
- Lower Master Valve (LMV)
- Upper Master Valve (UMV)
- Swab / Crown Valve (vertical access)
- Production Wing Valve (flow to flowline)
- Kill Wing Valve (annulus injection or well kill)
Note on Valves: Individual API 6A gate valves, ball valves, and chokes used in Christmas trees are detailed in our dedicated [Valves] section. This page focuses on the complete assembly scope.
2.2 Horizontal Trees
The master valve and flow path are oriented horizontally. The tubing hanger is installed in the tree body, not the wellhead. Allows tubing retrieval without removing the tree.
- Advantages: Faster workovers, simpler subsea installation, reduced rig time
- Applications: Subsea wells, platform wells with frequent intervention
- Standard: API 6A / API 17D (subsea)
2.3 Tree Components
- Tree Block / Body: Solid forged or cast block containing internal flow paths and valve cavities
- Tree Connector: Hydraulic or mechanical connector to wellhead (especially subsea)
- Flowline Connector: Flanged or clamped connection to production flowline
- Tree Cap: Pressure-containing cap for top of tree (vertical) or end of tree (horizontal)
- Gauge / Instrumentation Ports: Connections for pressure and temperature monitoring
3. Completion Tools
Downhole tools installed as part of the completion string to isolate zones, control flow, and enable future intervention. Designed and manufactured to API 11D1.
3.1 Packers
Downhole isolation devices that seal the annulus between the tubing and casing. Essential for zonal isolation, production segregation, and safety.
| Type | Description | Application |
|---|---|---|
| Production Packer | Permanent or retrievable seal between tubing and casing | Zone isolation, commingled production prevention |
| Service Packer | Retrievable packer for temporary operations | Fracturing, acidizing, well testing |
| Tension Packer | Set by tubing tension | Shallow wells, workover operations |
| Compression Packer | Set by tubing weight | Deep wells, HPHT environments |
| Inflatable Packer | Inflated by fluid pressure, conforms to irregular borehole | Open-hole completions, damaged casing |
| Permanent Packer | Set once, cannot be retrieved. Milled for removal | Long-term zonal isolation |
| Retrievable Packer | Can be released and recovered on tubing | Workover or recompletion planning |
3.2 Bridge Plugs
Isolate the wellbore below the plug. Used for temporary or permanent zonal abandonment, stimulation diversion, or pressure isolation.
| Type | Description |
|---|---|
| Cast Iron Bridge Plug | Permanent. Milled for removal |
| Composite Bridge Plug | Permanent. Easier to mill than cast iron |
| Retrievable Bridge Plug | Removable on slickline or coiled tubing |
| Frac Plug | Isolates zones during hydraulic fracturing. Typically composite, millable |
| Through-Tubing Bridge Plug | Set through existing tubing to isolate lower zones |
3.3 Sliding Sleeves (Sliding Side Door – SSD)
A downhole valve with a movable inner sleeve that opens or closes ports in the outer housing. Provides selective communication between the tubing and annulus.
- Operation: Mechanical shifting tool on slickline, coiled tubing, or wireline
- Applications: Selective production from multiple zones, gas lift injection, chemical injection, circulation during completion
3.4 Landing Nipples
Precision-machined profiles installed in the tubing string to receive and lock specific downhole flow control devices.
| Type | Application |
|---|---|
| XN (No-Go) Nipple | Has an internal shoulder. Locking device lands and seals. Most common |
| RN (Selective) Nipple | No internal shoulder. Locking device locates in profile grooves |
| Safety Valve Nipple | Landing profile for subsurface safety valve |
| Gas Lift Nipple | Landing profile for gas lift valve mandrel |
3.5 Gas Lift Mandrels & Valves
Installed in the tubing string to inject gas from the annulus into the production tubing, reducing fluid density and lifting produced fluids to surface.
- Side Pocket Mandrel: Houses retrievable gas lift valve. Valve can be changed by wireline
- Conventional Mandrel: Gas lift valve threaded directly into body
4. Liner Hangers & Accessories
Suspend and seal a liner (casing string not run to surface) from the previous casing string.
- Mechanical Liner Hanger: Set by rotation and weight
- Hydraulic Liner Hanger: Set by applied pressure
- Liner Top Packer: Seals annulus above liner hanger
- Tie-Back Receptacle: Allows tie-back string to be connected to liner top
Standard: API 10D (bow-spring centralizers), API 11D1 (packers and bridge plugs)
5. Downhole Flow Control
5.1 Subsurface Safety Valves (SSSV)
Fail-safe closed valves set deep in the wellbore to shut in the well in an emergency. Controlled from surface via hydraulic control line.
| Type | Description |
|---|---|
| Tubing-Retrievable (TRSV) | Integral to tubing string. High flow capacity. Tubing must be pulled to replace |
| Wireline-Retrievable (WRSV) | Set inside a safety valve landing nipple. Retrievable by wireline without pulling tubing |
| Subsurface-Controlled (SSCSV) | Closes automatically when flow rate or velocity exceeds a preset limit. No surface control line |
Standard: API 14A
5.2 Downhole Chokes
Installed in the completion string to control flow rate or pressure drop downhole rather than at surface.
- Applications: Manage drawdown, prevent sand production, control injection profile
- Trim: Tungsten carbide or ceramic for erosion resistance
6. Wellhead Accessories
6.1 API 6A Ring Gaskets (RTJ)
Pressure-sealing gaskets for wellhead and Christmas tree flanged connections.
| Type | Description |
|---|---|
| Type BX | For 6B flanges (up to 5,000 psi). Octagonal cross-section |
| Type RX | For 6B and 6BX flanges. Pressure-energized |
| Type SRX | Sour service variant with controlled hardness |
| Material | Soft iron (standard), 316 SS, Inconel 825 (sour/high-temp) |
6.2 Stud Bolts & Nuts
High-strength fasteners for wellhead and Christmas tree flange connections.
- Standard: API 6A, ASTM A193 B7 / A194 2H (standard), ASTM A193 B7M / A194 2HM (sour service)
- Coatings: PTFE, Xylan, hot-dip galvanized, zinc-nickel
6.3 Wear Bushings
Protective sleeve installed in the wellhead during drilling operations to protect the casing hanger landing shoulder and seal areas from drill string wear.
- Running Tool Compatibility: Matches drilling BHA handling equipment
- Retrieval: On drill pipe or dedicated retrieval tool
6.4 Test Plugs & Test Tools
- Cup Testers: Test casing or tubing before running completion
- Test Plugs: Seal wellhead bore temporarily for hydrostatic testing
- Back Pressure Valves: Installed in tubing hanger to isolate wellbore during tree installation
7. API 6A Classification (Wellhead & Tree Equipment)
| Classification | Parameter | Options |
|---|---|---|
| Pressure Rating | Maximum working pressure | 2,000 / 3,000 / 5,000 / 10,000 / 15,000 / 20,000 psi |
| Material Class | Service suitability | AA (General) to HH (Severe Sour) |
| Temperature Class | Operating range | K (-60°C) to Y (+345°C) |
| PSL (Product Specification Level) | Quality & testing rigor | PSL 1 (basic) to PSL 4 (maximum) |
8. How We Support Your Wellhead & Downhole Requirements
- Complete Assembly Supply: We source fully assembled and tested wellhead and Christmas tree packages—not just loose components
- Documentation Dossiers: Full MTRs, hydrotest records, and API 6A compliance certificates for every assembly
- Sour Service Expertise: We understand NACE MR0175 material class matching across all wellhead components—a critical but often overlooked detail
- Project-Specific Configuration: We review your well schematic and recommend compatible component combinations
9. Cross-Reference with Valves Section
Individual API 6A gate, ball, and choke valves—which are components of Christmas tree and wellhead assemblies—are detailed in full in our [Valves] section. This page focuses on the system-level assembly, structural components, and downhole tools that are not covered elsewhere.