Proposal for a Recommended Practice: Extending the design life of surface barriers of producing wells
Many oil and gas platform installations are operated beyond their original design life. This is managed by operators by means of a Life Time Extension (LTE) process to demonstrate that continued operation throughout the expected extended life is safe. The existing LTE guidelines address most parts of the installation, e.g. structural, safety systems, etc. There is however not an agreed industry practice for a LTE process for surface wellhead and X-mas tree systems.
Ocean Maxwell has performed a study on this important subject, summarized in the report “ Life time extension for surface wellhead and X-mas tree systems". The report includes a proposed scope for re-qualification of the wellhead and X-mas tree systems, based on earlier performed LTE processes.
Surface X-mas tree and wellhead systems are qualified according to the industrial standard API 6A / ISO 10423 and have a specified design life which can vary from 15 to 25 years. Both the X-mas tree and the wellhead systems maintain the secondary well barrier functionality for an event of primary barrier failure downhole. The X-mas tree system is also part of the installation safety system (ESD system). The systems shall not be operated beyond the design life of the equipment without a LTE process performed, demonstrating there is sufficient integrity to continue safe operation throughout the life extension period.
The ageing process of wellhead and X-tree systems introduces an increased risk element for the Health Safety and Environment on mature installations if well barrier systems are not assessed appropriately during the Life Time Extension (LTE) process of the mature installation. One of the main risks which should be assessed in detail is the effect of the degradation mechanisms of materials and how these affect the primary and secondary well barrier over time. The reliability of the secondary well barrier becomes even more important if the reliability of the primary well barrier components decreases due to ageing, cycling, fatigue, etc.
The Ocean Maxwell report presents a review of documents and experiences related to well integrity and/or well life time extension. There are numerous industry guidelines and reports for LTE of offshore facilities and specific systems available, however the basic principles for LTE processes do not define a required minimum scope for extending the design life of surface wellhead and X-mas tree systems. Many of these systems, or components thereof, are assumed to be operational beyond their intended service life on the NCS, without appropriate assessments of these systems performed.
The responsibility for the overall system integrity for well barrier systems lies by the E&P operator as duty holder. The duty holder shall demonstrate that there is sufficient technical, operational and organisational integrity to continue safe operation throughout the life extension period.
The oversight of such process would be with the Safety Authorities who give consent to continue operations. Due to the complexity of the well system LTE processes, it is recommended that an independent external verification on well barrier systems is performed, until a Recommended Practice is in place.
It is proposed that the industry prepares a Recommended Practice for LTE assessment for ageing wells. This report provides a starting point and scope for such Recommended Practice.
Contact us for further information to get a presentation on the subject, info on how to get access to the report, or to get support from our LTE team of consultants.
Cecilie Sælen, General Manager
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