This document describes the minimum requirements for surface wellhead equipment, including casing head housing or spool, tubing head, tubing hanger and any associated equipment.
1. REFERENCES
API Spec 6A
Pressure Testing Standard
HPHT wells Standards
NACE MR-01-75
API 6FA
SI 913.
2. GENERAL
1. Whenever possible, a monobore or uni-head type wellhead system is preferred in order to minimize BOP handling.
2. All wellhead equipment shall comply with API latest edition, inclusive of all its appendices. Purchase orders will specify the appropriate PSL (Product Specification Level) to suit the application, as described in table 3 which is based on the API 6A specifications.
3. Wellheads shall be rated for the maximum expected pressure during the lifetime of the well in addition to the criteria given in WOR 15 - Pressure Testing.
4. Consideration should be given to:
a. Shut-in pressures.
b. Test pressures.
c. Squeezing pressures (stimulation - acidizing, fracturing).
d. Injection pressures
5. Wellheads and elastomers shall be rated for the maximum and minimum temperatures expected during the life of the well, particularly when gas lift is anticipated.
6. Elastomers shall be chosen with due regard to any well fluids and/or production chemicals (corrosion inhibitor for example) or cuttings re-injection fluids which they may come in to contact with.
7. Wellheads shall have H2S trim in areas where H2S is known or perceived to be a hazard (Cat 1 or Cat 2) both during initial well operations and for the lifetime of the well.
8. Wellhead sections shall have outlets allowing the monitoring of any pressure build-up in the different casing annuli.
9. Casing annulus pressure shall be monitored whilst pressure testing and shall be checked daily during Well Operations. It must also be checked every day during Workover / Intervention operations.
10. Casing head housings or spools giving access to annuli where hydrocarbons might be present shall be fitted with two fully equipped side outlets. Additionally, they shall feature VR plug threads and enough space to hook up a VR plug installation tool & lubricator.
11. A fully equipped side outlet shall feature two x 2 1/16" gate valves in series See wellhead diagram & Tables 1 & 2.
12. Side outlet valve metallurgy shall be compatible with the wellhead housing metallurgy.
13. Solid body bull plugs should never be used in a wellhead hook-up, hollow-core bull plugs incorporating a needle valve for pressure relief should always be selected.
14. Pressure gauges fitted on casing head housings or spools shall be of a realistic range, for the duty envisaged.
15. Protection of the inner string seal bore by a wear bushing (or bowl protector) is required at all times during Drilling, Logging, and Workovers where possible, to prevent damaging the sealing areas.
16. Wellheads must always offer the possibility of locking the casing hangers.
17. The wellhead vendor must show and prove that the seal assemblies of the different casing hangers have been pressure tested from below at least during the qualification tests in working characteristics conditions of pressure and temperature (Max working pressure and Maximum working temperature).
3. REQUIREMENTS
To ensure well integrity, the following equipment is required:
Note 1: The working pressure of these valves should be ≥ the casing/tubing spool working pressure. If frequent bleed off is required of the considered annulus for accurate monitoring, an additional choke and adequate bleed off arrangement is mandatory.
Note 2: See General point 9. If frequent bleed off is required of the considered annulus for accurate monitoring, an additional choke and adequate bleed off arrangement is mandatory.
Note 3: The SCSSSV must be installed deep enough below the surface or mud line to remain operational in the case of damage to the wellhead or X-mas tree: for onshore or subsea wells, 50m is the minimum depth requirement. For platform wells, 20m below the deepest platform pile or conductor pipe constitutes the minimum depth requirement.
GENERAL RULES
1. Wellhead annulus valves shall require PSL-3G certification if the outer casing of the subject annulus requires gas tight connections in accordance with the casing design manual DOP-DR-P-15-004 which states that gas tight connections shall be used for the following:
a. Production tubing
b. Production casing (tubing x casing annulus)
c. Production liners
d. Intermediate casings where there are permeable hydrocarbon bearing zones or where there is a history of live annuli during the life of the well.
Otherwise PSL 3 shall be required.
2. All Wellheads and Xmas Trees for use by ENGIE shall be manufactured in accordance with API Specification 6A, API 6FA and SI 913 latest editions. Offshore EU wells are governed by EU Directive 2013/30/EU. The relevant PSL level/s should be chosen from table 2.
3. All Wellhead and Xmas Tree equipment as part of a Safety Critical System shall be subject to Independent Design Review, Manufacturing and Certification by a recognised Independent Verification Body (IVB) e.g. Lloyds, DNV. (See Table 2 for IVB deliverables)
4. Wellhead and Xmas Tree manufacturers shall be API approved and/or hold ISO 9001 or equivalent accreditation.
5. The manufacturer shall provide an order/ contract specific Quality Control Plan for approval.
6. A competent person shall be appointed to review and approve the Manufacturer’s Quality Control Plan.
7. A competent person shall be appointed to attend the Manufacturer’s Pre Production Meeting.
8. A competent person shall be appointed to witness and monitor the manufacturing process and review the documentation in accordance with the approved Quality Control Plan.
9. All Wellhead and Xmas Tree equipment shall be commissioned as part of the Well hand over process.