Challenges of Offshore Gas Lift Break-out session API/ASME Gas Lift Workshop 4-5 Feb 2009 Wim der Kinderen Senior Production Technologist Shell EP Europe, Aberdeen

50 wells 230 wells 50 wells Gas lift in Shell EP Europe - dimensions

Why is subsea GL challenging? Need to design for the life of the well –Compromising number of valves, lift depth, orifice size Expensive interventions –Few GL valve change-outs and flowing pressure surveys Risk of hydrates –Gas quality and adherence to operating procedures are critical Wells are typically commingled –Over-injection causes back-out/deferment Well testing causes deferment –Limited (quality) test and survey data available –System and well model calibration is therefore cumbersome

Some questions How do we fill the gaps when data are missing? –Alternatives for well testing, gas lift flow metering etc How useful/accurate are our models to optimise lift gas distribution? –How often do we verify models with multi-rate tests? How do we manage flow assurance? –How do we prevent and cure hydrate problems? What are the critical success factors for a GL valve change-out? –Contingency? Wireline crew competency? How do we manage well integrity? –How often do we test for tubing-to-annulus communication? –Who decides about dispensation?

Discussion summary (1) How do we fill the gaps when data are missing? –Use a (physical) model to complement what is not measured –Assign confidence levels to data –Model accuracy increases with more and better data –Trending of data can make models more accurate –Define points in the system where totals are measured and work back to the wells –Make use of transients, e.g. when a well goes down the drop in total system production will reflect that well’s production –Lack of data is no excuse for not maintaining models, it just becomes more tedious and laborious –Involve field personnel in optimisation, this will help improve (well test) data quality –Spend more time training field personnel; they are interested and keen

Discussion summary (2) What are the critical success factors for a GL valve change-out? –There is a global problem with wireline crew competency –Verify that the services contractor sends his most experienced wireline operator –Kick-over tools must be in tip-top (= new) condition –Make sure we have the right valves, never use re- conditioned valves –Elastomers must be the best available to prevent sticking –All well work activities need to be reported in detail –Operating company expert should supervise all well work –New ISO standard may help ensure that crews test all equipment

Discussion summary (3) How do we manage well integrity? –Start with frequent testing, then reduce frequency to e.g. 6 months –We need testing standards, based on parameters that can be measured in the field (pressure dP/dt) –Dispensation should take into account risk assessment –In the UK, the government typically follows operator recommendations –As we see more and more offshore and subsea wells being gas-lifted, this subject should get a lot more attention