Southwestern Barents Sea

Late Jurassic-early Cretaceous caprocks of the southwestern Barents Sea fracture systems and rock mechanical properties... 

Cap rock problems and hydrocarbon leakage in the southwestern Barents Sea... 

Several explanations for hydrocarbon leakage in the southwestern Barents Sea have been attempted. Although tilting of fault blocks and lack of continuity of the cap rocks may provide the simplest explanations, modelling suggests that other mechanisms must... 

The southwestern Barents Sea continental shelf is dominated by ENE-WSW to NE-SW, and NNE-SSW to NNW-SSE trends with local influence of WNW-ESE- to E-W-striking elements (Faleide et al., 1984, 1993 Gabrielsen et al., 1990). In the southern part of the Barents Sea, a regional ENE-WSW grain is defined by the major fault complexes bordering the Hammerfest and Nordkapp Basins. To the west and northwest, N-S trends prevail (Tromsp Basin, Knplegga Fault, Homsund Fault Complex). 

Fig. 1. Main structural features of the southwestern Barents Sea, and locations of wells used in the present study. Geology after Gabrielsen et al. (1990).

Teistengrunnen Group (Fig. 2) commonly provide the hydrocarbon seat in the basin areas of the southwestern Barents Sea. These are predominantly dark grey to brownish shales and pyritic mudstones interbedded by stringers of limestones. The Hekkingen Formation may locally contain dolomites, silt and sandstone (Dalland etal., 1988). 

Rubble zones are very common in cored mudstones and shales in many regions of the Norwegian continental shelf, and the southwestern Barents Sea seems to be no exception. Three types of rubble zones are recorded in the wells investigated. 

Distribution of different fracture types cap rocks of the southwestern Barents Sea (see Table 1)... 

Fig. 7. Subsidence curves for the southwestern Barents Sea. (a) Bj0m0ya Basin (Brekke and Riis, 1987). (b) Bj0m0ya Basin (Roufosse, 1987). (c) Troms0 Basin (Brekke and Riis, 1987). (d) Hammerfest Basin (Brekke and Riis, 1987). (e) Loppa High (Roufosse, 1987).

Finally, the question arises whether it is possible to correlate the fractures mapped in the rocks of the Teistengrunnen Group to the established events of the tectonic history of the southwestern Barents Sea. Since the deposition of the sediments of the Teistengrunnen Group in the late Callovian (locally late Ba-thonian) to the early Ryazanian (Dalland et al., 1988), the different structural elements of the study area un-... 

It is found that the cap rocks of the Teistengmnnen Formation in the southwestern Barents Sea most probably were affected by fracturing during burial and/or unroofing. The frequency of fractures related to these events seems to be low, however, and they are regarded as a minor risk for hydrocarbon leakage on the regional scale. 

It is concluded that the relation between cap rock quality, uplift and erosion and tectonic reactivation and hydrocarbon leakage in the southwestern Barents Sea is still obscure, and will remain so until more rock mechanical data from the cap rocks become available. It is, however, still possible to assess a risk evaluation on both regional and field scales by applying the data presently available form the area. 

Gabrielsen, R.H., Grunnaleite, 1. and Ottesen, S. 1992. Reactivation of faults complexes in the Loppa High area, southwestern Barents Sea. In T.O. Vorren, E. Bergsager, 0.A. Dahl-Stamnes, E. Holter, B. Johansen, E. Lie and T.B. Lund (Editors), Arctic Geology and Petroleum Potential. NPF Special Publication 2. Elsevier, Amsterdam, pp, 631-641. 

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