Use of pore pressure data from the Norwegian Continental Shelf to characterize fluid-flow processes in geological timescales

Fridtjof Riis,Anke Wolff

doi:10.1144/sp495-2018-176

Abstract

Abstract A dataset with pore pressures from more than 1000 exploration wells has been used to investigate the dynamics of aquifer systems in the Norwegian Continental Shelf (NCS). Variations in aquifer pressures reflect flow of porewater through permeable rocks over geological time. Strongly overpressured regimes are formed within confined aquifers in subsiding areas, where fluid flow out of the aquifer is controlled by vertical seepage. In transitional pressure regimes, fluid flows within permeable beds towards areas with hydrostatic pressures. In the hydrostatic regime, pressure differences result from density differences due to varying formation water salinity and by hydrocarbon columns. An underpressured regime has been encountered in confined aquifers in the platform areas of the Barents Sea, and is related to net uplift and erosion. In the case studies, pressure differences are interpreted in the context of the relevant pressure regime, and with a dynamic approach where segment boundaries and cap rocks are regarded as low-permeability restrictions rather than barriers. The present distribution of pressure regimes was developed over the last few million years due to rapid Pleistocene sedimentation and erosion processes.

Highlights

In the reservoirs and aquifers of the Norwegian Continental Shelf (NCS), areas of overpressure, underpressure and regional overpressure gradients are widespread
The interpretation is based on many years of regional mapping and field studies of the NCS, where studies of pore pressures have been integrated with seismic interpretation and well correlation (Riis et al 2010)
Pore pressure will increase in a compacting unit if the permeability of the rock is not sufficient to allow a rate of fluid expulsion which matches the rate of compaction

Summary

G Garn T Tilje

Formation in the northern saddle (Fig. 12b). Deeper contacts are shallower than the mapped deeper sadoil–water contacts occur in the Garn Formation in dle. Low permeabilities, residual hydrocarbons, small pore volumes and which cover areas typically less than 100 km2 Another group of wells encountered severe underpressures ranging from 10 to 60 bar below hydrostatic pressure in the Fingerdjupet and Maud basins in the deeper parts of the Bjørnøyrenna Trough (Figs 1, 19 & 21). These severely underpressured aquifers are found in Triassic and Jurassic formations at depths of between 1000 and 2000 m (Fig. 23). This geometry suggests that there may be communication between the Snadd and Realgrunnen aquifers Both the Skarv and Goliat fields exhibit subtle pressure differences across segment and stratigraphic boundaries but, unlike Skarv, the Goliat delta_P values do not have obvious directional trends. Subtle variations in oil pressure occur in all wells and between wells (Fig. 24), suggesting moderate to poor communication

Discussion

Conclusions