Gas Lift Operations in Apache’s North Sea Region
Ross Littlewood
Peter Sordyl
Apache North Sea
Abstract
The Forties Field is located in the UK sector of the North Sea and has been operated by Apache North Sea Ltd. since 2003. The field consists of five production platforms and one subsea tieback. There are approximately 90 online wells and the Field production is around 60,000boepd. Approximately 40% of these wells are gas-lifted; the remaining wells haveElectric Submersible Pumps (ESP) installed.In December 2011 Apache took over the operatorship of the Beryl field with its two production platforms and associated subsea tiebacks. This added a further 50,000boepd to the region and another 44 wells. The Beryl wells are either gas-lifted or naturally producing.
Artificial lift is an essential part of Apache North Sea’s operations, however, the selection process between ESP and gas-lift is often not clear cut and has evolved over time to meet the changing requirements of the assets; this is particularly relevant in the Forties Field. Factors affecting the artificial lift selection include gas availability,topsides plant constraints, sand production, well productivity, and ESP run-life. Long term planning and detailed production forecasts are also a key requirement ofthe artificial lift selection strategy.
An understanding of gas-lift systems is an essential part of effectively delivering the artificial lift strategy, however, it has been seen that this can sometimes be lacking in both onshore and offshore staff. At times this has had an impact on operations; consequently training and coaching have been necessary to ensure that systems are properly designed and operated in such a way to maximize production. Good record keeping and data storage are important parts of understanding any assets gas lift wells and should not be overlooked.
In 2008 Apache began to run permanent downhole pressure and temperature gauges in selected gas-lift wells; this approach will also be applied to the Beryl wells on the current drilling plan. The data from the downhole gauges is continuously streamed onshore via a fiber-optic link and this has proved invaluable to the onshore engineers especially when troubleshooting problem wells. In addition to this, a distributed temperature system (DTS) has been installed in one Forties well which, coincidently, suffered major operating issues when the deep-set production packer became unseated. Evaluation of the DTS data concluded that changing out the gas-lift orifice would help to optimize the well which avoidedan expensive workover.