A Life-Cycle Comprehensive and Evolving Asphaltene Management Strategy of Sour MGI Oil Fields of South Oman

Abstract

Abstract The current paper provides actual learnings and new-technology application based evolving and holistic asphaltene management strategy for reservoirs which are under depletion or gas-injection; and are either currently facing or are potentially asphaltene-prone in future. The paper covers a life-cycle approach option both short- and longer-term potential asphaltene mitigation or solutions. South-Oman stringer reservoirs are carbonate bodies encapsulated in thick salt, reservoir pressure in these stringers vary from lithostatic to hydrostatic regime. Asphaltene Screening was done as part of Flow Assurance studies e.g., compositional SARA Analysis, De-Boer- Screen and PVT-lab experiments for assessing impact of gas injection on Asphaltene-onset-concentration and onset-pressure (AOC/AOP); it indicated one of the reservoir fluid SKY-3A to be asphaltene prone. The asphaltene issues in initial development phase and current miscible-gas-injection (MGI) phase have been/are being addressed with mixed successes and evolving learnings. Some of the reactive approaches applied are periodic solvent wellbore clean-out; while proactive methods include annual well-drift, real-time data trends monitoring, proactive planned clean-outs, installation of Magnetic Fluid Conditioner (MFC) to delay the precipitation with continuous revision and development of the tool design based on its performance. Also, standard strategy issued for safer interventions on Asphaltene wells based on learnings from historic issues. Producers during early depletion phase, faced no issue with asphaltene plugging, possibly due to high producing rate and pressure. However, during late depletion phase, severe wellbore and tubing plugging observed in some wells which was dealt with proactive drifts and coiled-tubing clean-outs (CTCO). MFC tool was installed in 4 wells with planned extension to most wells, as well as periodic well- drift monitoring which helped reducing the CTCO requirement frequency, however eventually asphaltene issue occurred even in MFC wells needing expensive work-over route for clean-outs. These learnings resulted in modification in approach with a more hybrid- approach of MFC and periodic solvent bullheading with Lab testing for asphaltene inhibitor squeeze treatment which also provides a surface solution for asphaltene plugging issues in flowline via periodic flushing practice. For gas injectors, automated Hall's plot to monitor well injectivity and well drift confirmed no asphaltene issue. Success criteria for solving producers included no/limited asphaltene-deposition in wellbore and well productivity deterioration, reduction in deferment and interventions as compared to previous year values. The asphaltene related flow assurance issues can be a complex and niche area. The paper describes actual experience shared from SKY- 3A reservoirs’ issues management, learning/evolving including new-technology trials of MFC and development of tool including future options e.g., other chemical inhibitors and solvents application on downstream and upstream-systems, chemical-injection via velocity- strings and other techniques. The evolving approach could be beneficial for similar depletion or gas-injection settings elsewhere, and helpful in field development planning, deferment reduction and asphaltene well reservoir management leading to operational excellence.