In situ stress from breakouts in the Danish sector of the North Sea

Borehole breakouts from 26 wells situated in the Danish Central Graben and one well situated in the northwestern section of the Ringkobing-Fyn High have been studied. The data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4.7 km. Statistics were used to obtain a mean azimuth of breakouts for each well, and each individual breakout was weighted by its length. Data quality of breakouts is assigned according to the World Stress Map quality ranking scheme. The breakout data reveal that S-H orientations in the Danish Central Graben are extremely scattered; no regional trend in mean S-H orientation can be identified as a result of the large standard deviation (+/-77 degrees). Similar scatterings of S-H orientations have been reported from adjacent regions of the North Sea. The results indicate that the state of stress in the sedimentary cover of the Danish Central Graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms. Three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the Post Chalk Group, Chalk Group and Pre Chalk Group. (C) 1997 Elsevier Science Ltd.