Integrated gas field development: The Anjum story

In contrast to oil field development, gas field development requires tight integration of subsurface, surface and economic issues due to the difficult y of storing surplus produced gas and the large effect of the back-pressure s in a surface network on the individual well performance. As a major gas s upplier the Shell Group, and in particular NAM, has extensive experience in this field. The gas production from onshore fields in the North Friesland area is a rec ent NAM development. A 10 million cubic meter per day LTS gas treatment ins tallation located near the village of Anjum came on stream in 1997. Product ion initially started from 3 wells in 2 fields to deliver gas to the Gasuni e grid at Grijpskerk. The total area comprises 10 fields and 4 remaining pr ospects and is planned to be fully developed by the year 2001, using wet ga s pipelines to route the production to either the Anjum LTS installation or the Grijpskerk SilicaGel installation. The Rotliegend reservoirs in this part of the Netherlands are very heteroge neous and require a more detailed subsurface simulation than feasible with the standard NAM tool for gas field development (GENREM). In addition, the area is close to the Waddenzee and based on extensive ecological research, NAM uses a stringent, self-imposed ecological constraint, whilst evaluating the development plans for this area. Detailed subsidence studies have been run using subsidence-modeling tools, which run under a software user-inter face called FrontEnd, an in-house development by the Shell Group. Also runn ing under this interface is an application for gas field development called Gas Field Planning Tool (GFPT). GFPT combines a detailed subsurface simula tor with a surface simulator using a development planning module, which han dles economic and operational aspects of the integrated model. Lastly, the interface gives access to a powerful command language and a mathematical to olbox, which can be used to define almost any missing functionality. Making use of the flexibility offered by the FrontEnd interface and with he lp from available expertise in RTS (Shell Rijswijk), an integrated GFPT mod el was built, which not only incorporates operational and economic constrai nts, but also does optimization and subsidence analysis. The model is used to evaluate all development options and scenarios for this area in a consis tent manner. Therefore, all proposed development plans are optimized within all applied constraints whether they are related to surface, subsurface, e conomic, or environmental aspects. Production history and well performance are very close to those predicted b y these detailed models, which will allow accurate prediction of future fie ld performance and subsidence.