Wellhead Inspection and Maintenance
Mechanical assemblies are susceptible to corrosion, wear and tear, and other unforeseen damages. It is therefore essential that plans are put in place for routine wellhead installation maintenance operations such that problems can be identified from the onset and remedied quickly.
In order to safe guard asset structural integrity, it is increasingly important to adequately service and maintain wellhead and christmas tree assemblies to confirm the integrity is fit for purpose and ensure surface barrier against hydrocarbon leakage and reliability in an emergency situation.
This cannot be over emphasized if the consequence of a failure of the installation is imagined. The risk of a catastrophic failure occurrence, which leads to significant financial implications and bad reputation, is greatly reduced. Proactive, regular maintenance is a more cost effective approach than reactive maintenance. It ensures compliance with Health, Safety and Environment (HSE) standards and promotes efficiency and effectiveness.
In order to reduce the financial implications of a wellhead maintenance campaign, it is common practice to keep the replaced assemblies in a refurbished stock pool. By stripping the assemblies down and fully refurbishing each worn component, the item can be re-stocked and used at a later date when that particular item is required for another well. Over a period of time, the refurbished stock will increase to a point where the operator has access to a large set of spares which will reduce the need to reverse engineer or buy new parts from an external supplier. By analyzing the common failure mechanisms of each component, trends can be identified which can be used to build up a check-list of common faults with particular wellhead designs which will then form part of the preventative maintenance inspections.
Once the critical maintenance activities have been completed, plans will be made for carrying out regular maintenance inspections and ensuring the integrity of the wellhead and surface installations are maintained. This is carried out on a rotational basis with scheduled visits to each well in turn. Before this can proceed, the wellhead team and the client must agree to acceptable operating limits for each wellhead variable. Examples of the typical variables that are recorded and monitored during each site visit are as follows:
- Functional testing of wellhead and tree gate valves (number of turns to open/close the valve)
- Pressure testing of tubing hanger and all casing hanger voids
- Pressure testing of the tree valves
- Actuator closure times and function testing (reaction time)
In addition to collating this information into a report for the client, it is beneficial to maintain a record of these readings over a period of time to monitor the gradual deterioration of a particular component or the increase in pressure at a particular location so that steps can be taken to alleviate the problem before the agreed limits are exceeded and it becomes a serious issue.