Efficient and Comprehensive Integrity Diagnostics for Dual Completion String Wells, Using Spectral Noise Analyzer Tool

Well operators often face various technical challenges when intervening and repairing older, mature field wells. The most common problem associated with aging wells are tubing and casing integrity. Uncertain sources of downhole leaks and data ambiguity often lead to incorrect diagnostics that can hinder repair work or even contribute to additional or worsened integrity issues. Operators continuously challenge service companies and technology providers to drive innovation. One such challenge is in finding efficient and comprehensive integrity diagnostics for dual-string wells. A basic and general diagnostic method to verify well integrity in dual-string wells involves setting plugs in the long and short strings and pressure testing the tubings. These operations are generally time consuming, and the test data does not usually pinpoint the location of the leak, if any. Since 2016 a new diagnostic solution for this challenge has been implemented using a slickline-deployed passive acoustic logging technique. Carefully designed intervention planning, combined with efficient data acquisition, led to significant time saving and improved data quality. A more complete assessment of the integrity of both strings is now more frequent and often necessary, while challenging the conventional thinking of having to assess the lower string only while assuming the upper string is in good condition. However, investigating dual-string integrity with uncertainty on the source of leak, restrictions on facilities and limitations on surveillance time will often waste more time and money if not approached carefully. This paper discusses two case studies, including a dual-string oil producer in the South China Sea that had sustained pressure in production casing annulus. The well operator initially considered that the long string had an integrity issue, while the short string did not, based on their surface-based annulus pressure diagnostics. Consequently, the operator decided to diagnose only the long string. The passive acoustic memory tool. combined with a fast-response temperature and spinner used for the diagnosis, identified a possible short string leak while logging through the long string. This result clearly demonstrated that surface analyses can be misleading, and a comprehensive downhole diagnostic should be the recommended method to identify leaks, especially in dual-string completions. This well operator has completed more than 100 integrity diagnostic runs in the last five years. The passive acoustic diagnostic interventions have resulted in an average 50-percent time saving compared to legacy methods, and data analysis results have led to significant improvements in well productivity.