Tayvis Dunnahoe
Exploration Editor
In production since 1965, the southern North Sea has long been perceived as a mature play with very few new opportunities. While the region's production has remained stable, operators focused in the region have been forced to look outside of the productive fairways and other areas to find additional reserves.
Despite the opinion that the southern North Sea has little left to offer, many exploration companies are revisiting historical data with newer seismic processing techniques—a move that has led to new field discoveries and perspective about the region against conventional wisdom.
"Statistics are not always the final answer," said Martin Fleckenstein, president, exploration, new ventures, Wintershall Holding GMBH. While speaking on the viability of discoveries made in mature basins at the European Association of Geophysicists & Engineers' annual conference on June 18, Fleckenstein said, "In many cases we've drilled against statistical probabilities."
Wintershall, a subsidiary of BASF, is active in many countries, namely Argentina and Chile, and in Russia. As the third-largest operator in Germany, the company also has had an active history in the southern North Sea. Fleckenstein pointed to the recent F17a discovery, which has proved reserves of 30 million bbl, in the Dutch North Sea (OGJ Online, Feb. 7, 2012) and the more recent Hibonite discovery in the Danish North Sea (OGJ Online, Mar. 27, 2013) as major examples of finding new resource potential in mature basins.
Mature basins, small operators
The ability to reassess mature basins has resulted in new opportunities for smaller operators. London-based exploration and production company Hansa Hydrocarbons holds 20% interest in the large B20008/71 license operated by Wintershall in the German North Sea (known as the H&L blocks). In January 2010, Hansa participated in the drilling of the L1-2 well with the objective of appraising the L1-Alpha discovery.
The L1-Alpha discovery was made in 1975 and proved gas in the Lower Rotliegendes Havel sandstones with a well flow test of 6 MMscfd. No gas-water contact was established with the well and, given the nitrogen content of 19% and the poor understanding of sand distribution, the discovery was left undeveloped.
"The L1-2 was the first well drilled in the area for over 30 years," said Joel Corcoran, new ventures manager at Hansa Hydrocarbons. Although the license holds three discoveries, the region has been overlooked because of the poor understanding of reservoir development in the Lower Rotliegendes sandstones.
With its unique position in the H&L blocks, Hansa has capitalized on its 4Quads project in the adjacent area. Hansa is 100% operator. In accordance with the Dutch Mining Law, EBN, the Dutch state entity, opted to participate in the licenses at a level of 40%. The 4Quads lie in 35 m of water some 40 km north of the island of Schiermonnigkoog and immediately west of the German-Dutch median line. The licenses, which comprise the G18, H16, M3, and N1 blocks, are contiguous with the German H&L blocks to the east where Hansa holds its 20% interest.
With new data and revised understanding, Hansa has developed the 4Quads prospect into a play extension. "With conventional prospective resources in excess of 2 tcf of gas in place, the 4Quads are a strategically significant resource for the Netherlands," Corcoran said. The company plans to acquire 965 sq km of 3D seismic over the 4Quads in the summer.
Preconceived ideas can be a limiting factor in exploring mature basins. "The newest generation of geologists should continuously look for new ideas, and develop their own opinions based on rigorous data exploration," Fleckenstein said.
