On the better late than never principle we report virtually from the 36th gas lift workshop held in Stavanger Norway earlier this year, co-hosted by the Artificial lift R&D council and the International petroleum training institute of the American society of mechanical engineers.
Asbjørn Andersen (WellMaster) and Alan Brodie (PTC) presented Exprosoft’s reliability management system (RMS). The RMS is managed by ExproSoft as a joint industry project and is claimed to be the world’s largest repository of well experience data. RMS holds 20 years of data from 5,000 completions and 30,000 well-years of production. The data is used for vendor benchmarking, risk-based completion design and cost estimates of life-of-well intervention strategies. ExproSoft offers commercial added-value software and services to equipment suppliers and service companies. PTC showed how the RMS was used to evaluate the reliability of its own gas lift valves.
Shell’s Wayne Mabry discussed recent revisions to the API 19G2 standard for flow control devices. The API 11V1 spec for gas lift equipment was discontinued in 2012. Today the situation is complex with different ‘standard’ specs emanating from the API, ISO and Statoil. Meanwhile technology and deepwater requirements make for more complex use cases. Mabry observed that today, the ISO oilfield process has stopped and the standards are ‘stagnant.’ ISO and API are not working together and there is currently no mechanism for updating or improving the ISO document. All in all a standards ‘train wreck!’ There is some hope in the soon to be released API 19G2 document which will include Statoil’s requirements and should be the de facto industry standard—especially for deep Gulf of Mexico applications.
Bin Hu of Schlumberger’s SPT unit showed how Olga’s dynamic modeling was used to model and understand transient effects in situations such as slugging, thermal and liquid loading and artificial lift. For gas lift, Olga is used to model transient multiphase flow in tubing and annulus including thermal interactions, downstream and upstream boundary conditions including choke and gas lift valve characteristics. Another use case involved gas ‘robbing’ in dual completions which was shown to be eliminated by optimizing gas lift pressure.
Cameron Laing of Laing Engineering Training Services offered an iconoclastic look at ‘gas lift nonsense.’ Laing’s nonsense includes the observation that test rack pressure is regularly being set too high because of the use of a static temperature gradient. Valve set up is frequently sub-optimal and usually neglects valve aging. Few operators or service companies are interested in learning about valves’ true condition from tear-down inspections. And finally, operators frequently lose track of valve positions and keep poor reliability records. Finally, gas lift modeling frequently uses over simplistic models. Laing advocates use of Petex’ Prosper in this context.
Read the ALRDC presentations here.
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