Haltenbanken Hydrocarbon Province (Offshore Mid-Norway)

Rolf Magne Larsen, O. R. Heum

Exploration drilling at Haltenbanken started in 1980, and to date, 11 significant hydrocarbon discoveries have been made. The estimated total recoverable reserves are 310 million standard m³ of oil and condensate and 305 billion standard m³ of gas. Only 14 out of 25 wildcat wells were dry, giving a pure exploration success ratio of 44%.

The major structural elements at Haltenbanken are (from east to west) the Troendelag platform, the Halten terrace, and the Deep Moere basin. The major hydrocarbon discoveries are located on the Halten terrace and on the western margin of the Troendelag platform.

After a long period of regional passive subsidence during the Triassic and most of the Jurassic, the Halten terrace was formed as a consequence of Late Jurassic east-west rifting and Early to middle Cretaceous north-south dextral wrenching. During the Late Cretaceous and Tertiary, regional passive subsidence again dominated. In the Miocene, deep waters had developed at Haltenbanken, as well as over most of the middle Norwegian shelf. In the Pliocene, uplift of the Fennoscandian shield resulted in rapid westward shelf progradation and deposition of up to 1,000 m of sediments.

This Pliocene burial had a great impact on the formation and entrapment of hydrocarbons at Haltenbanken. As the temperatures increased, the rich Upper Jurassic marine and Lower Jurassic terrestrial source rocks passed into the oil window and are presently still producing large amounts of oil, condensates, and gas.

The rapid Pliocene sediment loading also led to great overpressure in the Upper Jurassic to Paleocene fine-grained sequence. In the eastern areas, this overpressure resulted in a perfect seal over the Middle and Lower Jurassic sandstone reservoirs. In the western areas, the Jurassic reservoir sequence also is severely overpressured, leading to less favorable sealing conditions. However, the overpressure in the reservoirs in the western areas seems to have reduced the rate of compaction, hence preserving the porosity and permeability better at great depths.

Seven of the most important discoveries at Haltenbanken serve as case examples. The variations in types of hydrocarbons (oil vs. gas or gas-condensates) entrapped in the individual fields are caused by subtle, but important, variations in source rock maturity, migration conditions (including drainage area and storage capacity), trapping conditions (fill-spill or fill-leak), timing, and pressure-volume-temperature conditions.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.