Well integrity can be a major safety concern at a certain age of any field. Evaluating wells at risk as a result of corrosion is essential to avoid production losses and/or well safety hazards. A new approach was developed and adopted in a recent well integrity study of a field with 40 wells of which half are quite old. The approach includes a method for integrating data from different sources and ranks the wells according to their integrity status and need for a workover.
Through surface inspection of a well the outer conductor and/or casing can be examined down to a depth of around 30 ft in this field. Below this depth corrosion logs are the only tool to investigate the inner and outer casings. Running new corrosion logs to evaluate casings integrity is costly and time consuming and requires a rig to pull the completion and scrape the casing before running the corrosion logs. To save time and money, the following approach was adopted to prioritize wells for inspection and work over:
Understand capabilities and accuracy of the old/current corrosion evaluation tools.
Re-evaluate all available corrosion logs for old wells.
Use well X-6 as a base case where two sets of corrosion logs were run with a time lapse of 7.5 years to understand the corrosion development over time.
Run corrosion logs in two representative pilot wells X-12 and X-18 to improve the understanding of the current situation.
Integrate all the data provided by the field engineers with the corrosion log results and prioritize the wells in terms of corrosion criticality and work over priority.
A scoring system has been developed for the well integrity evaluation to integrate different data such as casing age, presence of conductor, well surface inspection and corrosion logs results/reliability.
Two wells ranked as a top priority for work over. These were logged and were found to be severely corroded. Then they were abandoned and replaced. One of them is well X-6 which was considered as a blind test for the scoring system. Also the two wells categorized as a low workover priority were logged and found to be in good condition, confirming the reliability of the scoring system that had been established.