A new type of grid used in the dynamic simulation model of the giant Troll Field is presented. The grid consists of a stratigraphic and a horizontal layered part. Hence, it is named hybrid grid. The horizontal part encompasses the thin oil zone and a small distance into the gas cap and water zone, the rest of the grid follows the stratigraphy. The reason for choosing such a grid for the Troll Field is the dipping stratigraphic layering, a thin oil column, and the large area that the field covers.Another factor is the long horizontal wells that drain the oil. The horizontal grid has a high vertical resolution of 2 m to accurately capture the thin oil column, and for satisfactorily representing horizontal wells close to the fluid contacts. Above and below the horizontal grid the layers follow the stratigraphy to represent the geology with a minimum number of grid blocks. The paper shows why the hybrid grid is superior compared to other grid types for a gas field with a thin oil column, and covering a large area. The paper also describes how to build a hybrid grid, and the work processes for up-scaling and history matching the model. The new Troll model has currently replaced the 15 simulation models that previously were used to represent dynamically the Troll Field.

The Askeladd field was the first discovery of hydrocarbons in the Barents Sea. The discovery wells were drilled in the early 1980, yet the field remains to be developed. The field is part of the Snøhvit Unit that consists of the three main fields: Snøhvit, Albatross and Askeladd (see Figure 1). Snøhvit was set in production in 2007 and Albatross in 2010. Both fields are providing feed gas to the Hammerfest LNG plant (HLNG). The feed gas to the HLNG plant will start to decline in in not too many years’ time. In the business planning phase two measures to mitigate the decline was looked at: i) install an onshore compressor at HLNG, or, ii) start gas production from the Askeladd field. The startup of compression before all major resources is set in production violates the standard way of setting up a drainage strategy. However, for making decisions it is creating value that matters. The full life time production profile for HLNG did not show any significant difference between the two concepts. Since the onshore compression solution is slightly less costly than the development of Askeladd, that case was for a long time the strongest. It was not before the full profile was broken into single investment steps that the project showed that Askeladd was more economical. This process also brought to light why compression should not start prior to all major fields being set in production. Further maturation of the Askeladd project focused on maximizing production by drilling horizontal wells, and minimizing pressure drop in pipelines, subsea production system and wells. The risk of water production is mitigated by multiphase meters on each well, and the ability to shut off water producing zones in the wells (identified by tracers).