ABSTRACT: The Geology of Heidrum--a Giant Oil and Gas Field on the Mid-Norwegian Shelf

P. K. Whitley

The Heidrum field is located in the Haltenbanken region on the mid-Norwegian continental shelf, 165 mi from shore in water depths of approximately 1150 ft. The field was discovered in 1985 and appraisal drilling has subsequently confirmed a giant Cimmerian structure with hydrocarbons trapped in Jurassic sandstone reservoirs. The field has 750 MM bbl recoverable oil reserves, with associated gas reserves of 0.45 tcf and free gas reserves of 1.3 tcf. The accumulation extends over 14.4 mi² and was unitized in 1989 with 75% of the field in Block 6507/7 and 25% of the field in Block 6507/8.

The 6507/7 block was acquired by Conoco Norway and partners in 1984 in the eighth round of licenses offered by the Norwegian government. The acquisition was based on extensive in-house exploration regional studies, which identified a Jurassic rift element in Haltenbanken and the potential for the generation of liquid hydrocarbons.

The Heidrun structure is a large southwesterly plunging horst block on the southwestern flank of the Nordland Ridge and was formed during the Cimmerian extensional tectonic phase in the Late Jurassic-Early Cretaceous. The Heidrun reservoirs are severely truncated at the northern edge of the structure and are sealed by Cretaceous shales.

The Heidrun Jurassic reservoir rock, the Fangst Group and the Tilje and Are Formations, were deposited on the southeastern flank of the developing northeastern Atlantic Rift domain. Despite an overall transgressive regime, the interval was characterized by a high coarse-clastic influx from the elevated rift shoulders. The shallow burial depth (< 8100 ft) has limited compaction effects, and reservoir quality therefore is enhanced with permeabilities up to 10 d and porosities in excess of 30% in the cleaner sands of the Fangst.

The primary sources for the petroleum is the Upper Jurassic Spekk Formation, which is mature in the downdip areas 3-10 mi southwest and west of Heidrun. Therefore, fairly long petroleum migration paths are inferred.

A 5000-km-high resolution three-dimensional seismic survey was acquired in 1986. State-of-the-art processing of these data has led to a great improvement in quality over previous two-dimensional data. The three-dimensional data set forms the basis for detailed geologic and reservoir models. These models were used in the application for development consent, submitted to the Norwegian government in late 1989 by the Heidrun unit owners.

The current development plan proposes that exploitation of the Heidrun Field will be done using an innovative concrete tension leg platform with offshore oil loading, and transportation of the gas to shore by pipeline for onshore usage.

AAPG Search and Discovery Article #91000©1990 AAPG Conference-Giant Oil and Gas Fields of the Decade 1978-1988 Conference, Stavanger, Norway, September 9-12, 1990