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Abstract "G" field is a mature field that has been producing for 30 years from 4 platforms. 90% of the wells are on gaslift. Well integrity issues including tubing leaks are common because of corrosion on account of contaminants (CO2 60% and H2S 10 to 100 ppm) and erosion due to sand production. These problems are observed particularly in older wells, which were completed without corrosion resistant tubulars and any downhole sand control. Optimizing gaslift for hundreds of wells is challenging due to robbing effect in dual-string wells, months of lead time to secure slickline for gaslift valve change (GLVC) or to conduct pre-GLVC pressure surveys. In some cases, sand cleanout must be performed before well intervention which delays GLVC opportunities to increase production. In a recent drilling campaign, a smart gaslift completions system "D" was installed in one single-string well (G1) and one dual-string well (short-string G2-SS and long-string G2-LS) to overcome the challenges described earlier. This paper presents valuable lessons learned over a two-year period since these wells were completed. D system has variable injection orifice ports downhole which are electronically operated through a cable using a Surface Control System (SCS). Each production string can be installed with several orifice units at designed depths, with each unit having pressure and temperature sensors linked to PI system for remote monitoring. Gaslift configuration changes can then be implemented anytime by "push-of-a-button" without well intervention. In comparison, conventional gaslift valves must be configured at the onshore workshop to operate under specific injection or production pressures at downhole temperatures, and then transported offshore to replace existing valves via slickline; and this excludes time needed for downhole data acquisition, analysis and GLVC design. The technology provided live downhole static/ flowing data that allowed the valves to be configured for unloading both the wells and enabled incremental adjustments to deepen gaslift injection while the wells were flowing. This ensures single-point injection (no multi-pointing) and eliminates separate shut-in intervention for pressure surveys or GLVC. Installing D system, which is run as part of completion tubing, removes slickline intervention limitations in high-angle wells. One extra benefit specific to G1 well was that live D system data was used to confirm both surface pumping data and the effectiveness of post-completion acid stimulation carried out via bull-heading. Backup gaslift mandrels are recommended to mitigate the risk of cable damage associated with running the system in high-angle, dual-string wells. In future, for similar well types, this technology should be implemented with care and by considering spacing of well accessories on both strings. The upfront cost of D system is higher than a conventional gaslift, but its justification is in reduced operating cost over well life, which comes from eliminating slickline pressure surveys and GLVC (while reducing deferred production), as well as any delay in routine optimization through GLVC.
Hamid et al. (Mon,) studied this question.