North Sea Plug and Abandonment September 2016 2H helped a client schedule and prioritise plug and abandonment operations for old exploration wells in the North Sea. LOCATION North Sea, UKCS WATER DEPTH 115m Background An operator in the North Sea has a number of temporarily suspended exploration wells that were drilled in the 1980’s and need to be plugged and abandoned. It was unknown if the fatigue capacity of the wells was sufficient for the plug and abandonment (P&A) campaign to take place. Solution To determine whether there was enough fatigue capacity to carry out the planned work, 2H conducted an assessment of the fatigue damage accumulated in the casing, conductor and wellhead system during the original drilling and suspension operations. We focused on the two wells that were scheduled for plug and abandonment and used hindcast weather data to improve the accuracy of the historical assessment. Due to the unknown start date and length of P&A operations, we calculated the expected fatigue damage rate along the system in annual seastate conditions, and provided the maximum allowable duration of P&A operations for work conducted at any time of year. Two semi-submersible drilling rigs were considered when calculating the damage accrued during P&A operations. Challenges Initial analysis showed that the drilling and suspension operations had led to significant fatigue accumulation, particularly in the wellhead profile. This led to short allowable durations for the P&A operations. We overcame this by selecting a design fatigue factor appropriate to the level of risk involved at each stage of the P&A operations, considering when a hydrocarbon path to surface may exist. The refined approach to design fatigue factors ensured that sufficient fatigue capacity could be demonstrated to allow P&A operations to proceed. Results 2H’s in depth knowledge of riser casing, conductors and wellhead systems, and expertise in subsea fatigue assessments enabled our client to schedule the plug and abandonment operations as well as select the most suitable vessel for the job. Share this page Share on FacebookShare on LinkedinShare on TwitterShare on Google+ Services Production & Export Riser Concept Engineering Steel Catenary Risers Top Tensioned Risers Hybrid Risers Flexible Risers Composite Risers Subsea Jumper Spools Subsea Umbilicals Deep Sea Mining Integrity, Life Extension & Monitoring Riser Integrity & Life Extension Platform Well Integrity & Life Extension Subsea Wellhead System & Life Extension Machine Learning for Riser Engineering Riser System Digital Twin Drilling Riser Management Riser Monitoring System Engineering Inspection, Maintenance & Repair Anomaly & Incident Engineering Subsea Engineering Services Component Detailed Design Decommissioning Engineering Engineering Critical Assessment Installation Engineering Mechanical Connectors Offshore Renewable Energy Qualification Testing Verification & CVA Well Plug & Abandonment Drilling, Completion & Workover Drilling Risers Completion & Workover Risers Subsea Wellheads & Conductors Platform Conductors Well Engineering Minimum Facilities Platforms Conductor Supported Wellhead Platforms & CoSMOS Riser Delivery Management Get the latest riser insights!Receive our riser news, published papers and blog posts in your inbox monthly. Related SERVICES Decommissioning Engineering See all Services