All wells shall be operated within the safe operating limits, defined type of well service (e.g. production, injection) and well design life.
Alarms shall be used when required to ensure well integrity. The alarm levels shall be set within the safe operating limits. The alarm limits shall be evaluated for situations in which automatic shutdown is required. For injection wells, special considerations shall be given to avoid risk of out of zone injection. If the defined type well service or established operating parameters are planned to be changed, the well design shall be checked to assure that the existing design is able to handle the new scenario and loads. A MoC shall be carried out before changing any of these parameters.
As part of the well planning the following shall be established prior to well start up: a) a WBE maintenance program with test procedures and acceptance criteria; b) well start up and shut-in procedures;
1. pressure in tubing and accessible annuli; 2. temperature (well, flowline);
3. production / injection rates;
4. composition of production and injection fluid (including any production/injection through annuli); and
5. composition of annulus fluids.
All fluids shall be compatible with the exposed well material and existing well fluid composition.
Tubing and accessible annuli pressures, rates and temperatures shall be trended and compared to detect any leaks or anomalies. Valve positions shall be known at all times and normally kept in a position to enable monitoring.
8.7.1 Leak and function testing of well barrier elements
The ESD function shall be tested before operating the well. A sequential shutdown of valves is required and shall be verified. The requirements for closure time of ESD valves shall be assessed and defined for each installation and field, based on risk and operating well conditions.
All valves, available testable seals and lines which are part of the primary or secondary well barriers shall have a maintenance program and be periodically tested to verify its function and integrity according to section 15.
Minimum test frequency is defined for the WBEs in section 15. The test frequency should be regulated based on:
a) experience data;
b) changes of the well flow composition increasing risk of deposits, scale, corrosion, erosion and high production and injection rates.
The historic performance and reliability data used to justify a change in the test frequency shall be documented.
If a safety critical valve or seal fails, the root cause should be established and actions shall be taken to repair. Preventative maintenance/actions shall be implemented to reduce the likelihood of new failures. If a safety critical valve type has a failure rate on the installation which exceeds 2% within a 12 month period, measures shall be taken to improve the reliability of the valve type in general.
8.7.2 Monitoring of well flow
The well flow / injection fluids shall be systematically monitored and analysed to detect changes that may negatively affect the WBE such as corrosion, erosion, scale and wax deposits, and emulsions.
8.7.3 Casing and tubing annuli
Maximum and minimum operating annulus pressures shall be defined for all accessible annuli. The operating pressure range shall be set to ensure that the design limitations (load cases) and verified test pressures are not exceeded for the individual annuli/ exposed WBE. For annuli open to the formation, the minimum formation stress should not be exceeded unless this is a planned contingency during the well design (e.g. subsea wells where B-annulus is not cemented)
The following shall be considered when defining the operating range:
a) the effect of temperature changes (well stream, ambient) on the annuli pressures, especially during emergency shut down situations;
b) the available response time to bleed off or top up annuli; c) variation in the tubing and annuli fluid densities; and
d) occurrence of pressure communication between annuli or escalation of risk if such communication should occur.
The pressure in all accessible annuli shall be monitored and maintained within minimum and maximum pressure range limits. All accessible annuli should be maintained with positive pressure for leak detection
The annulus bleed system shall be liquid filled at all times if possible. When gas has been bleed off from the annulus, the annulus bleed system should be replenished with liquid. Hydrate inhibition shall be considered.
See Norwegian Oil and Gas Association Guideline no. 117 – Recommended Guidelines for Well Integrity for defining the annulus pressure operating envelopes.
8.7.4 Sand production
It shall be assumed that wells in sandstone reservoirs may produce sand. Sand production from each well should be monitored continuously or at frequent intervals (downhole, subsea or at surface). Threshold values for maximum allowable sand production should be established. Erosion loss in the flow conduit from the reservoir and to the entry of the first stage separator should be estimated or measured, and compared with maximum allowable wear loss.
When sand production occurs, efforts should be taken to reduce the effect of sand erosion.
8.7.5 Scale/asphaltenes/wax
Scale, asphaltene and wax deposits in the well could cause failure of WBEs. The effect of
injection/produced water on the production performance shall be known through studies and chemical analysis. When the operating conditions are within the scale formation regime, injection of scale dissolver and/or a scale inhibition programs shall be considered.
Injected chemicals shall have a confirmed compatibility with all well component materials and fluids that will be exposed including chemical injection lines.
8.7.6 Hydrates
The potential for forming of hydrates in flow conduits shall be assessed, with particular focus on DHSVs, tree valves, annulus bleed-down system and other WBEs that may be affected. Procedures for hydrate prevention (injection of anti-freeze agents) shall be established, including leak testing of valves, and when shutting in a well for a longer period.