Post glacial lithospheric flexure and induced stresses and pore pressure changes in the northern North Sea

We have compiled data on the least principal stress, overburden, pore press ure and stress orientation for 92 wells in the northern North Sea. These da ta show that the least principal stress is close to the overburden in the T ampen Spur indicating high horizontal stress in this area. Closer to the co ast, i.e. east of the Viking Graben the least principal stress drops signif icantly. Along with this spatial change in stress magnitudes, the orientati on of the maximum horizontal stress rotates from approximate to 100 degrees in the Tampen Spur to approximate to 80 degrees around block 35/9. Analyti cal and numerical models of plate flexure suggest that these observed later al stress variations are the result of deglaciation, superimposed on a regi onal stress field dominated by ridge push. The pore pressure in the northern North Sea roughly follows the stress tren d, i.e. high overpressures where horizontal stresses are high (Tampen Spur) and close to hydrostatic pore pressures east of the Viking Graben where st resses are decreased. This close relationship of pore pressure and horizont al stress suggests that they have the same source. We have modeled the pore pressure change expected from the poroelastic response to deglaciation. Th e results show that strong overpressures in the Tampen Spur appear to be ca used only partly by deglaciation and flexure. Other sources of overpressure , such as compaction disequilibrium also play an important role. (C) 2000 E lsevier Science B.V. All rights reserved.