The exploration experience from Midgard to Kristin—Norwegian Sea

Abstract

The Norwegian Sea exploration history is used to illustrate that we as explorers generally have a poor understanding/appreciation of the subsurface variation. Several alternative exploration models, rather than one based on the nearest offset wells or general trends, should be carried out in prospect evaluations in order to more accurately reflect the true uncertainty. Data on all scales from regional seismic to atomic need to be integrated and build the fundament for successful exploration models. It is important not to discard ‘outlier’ data points as these may hold the key to unlock as yet unrecognised values. The Norwegian Sea currently attracts the main focus of exploration drilling on the Norwegian shelf. Initial success was obtained on the Halten Terrace with the Midgard gas find in the third well. At the time gas was non-commercial and it was not until after the Tyrihans and Draugen oil discoveries that the province was considered commercial. This first phase of exploration saw many surprise results (e.g. oil rather than gas and vice versa, reservoir intervals and reservoir quality) and had an element of serendipity. More discoveries, including Smorbukk, Smorbukk Sor and Njord, were found before interest again tapered off in the late eighties. Disappointing exploration results to the north and south of the Halten Terrace resulted in a downgrading of the whole Norwegian Sea until 1991 when the Norne Field on the Donna Terrace sparked renewed interest. Well established exploration models on porosity destruction with depth were challenged and led to the Lavrans and Kristin discoveries in the Halten Terrace ‘dry belt’ in 1994 and 1997, respectively. However, surprises have also been present in the more recent drilling (e.g. hydrocarbon phases and reservoir thickness in Kristin and Lavrans) and illustrates that there still is a long way to go before all ‘subsurface secrets’ are unlocked.