Determination of the State of Stress by analysis of drilling-induced fractures-results from the northern north sea

摘要

Borehole failures like drilling-induced fractures and breakouts observed in image logs offer the possibility to derive high quality stress orientations. Image logs from 16 wells in the Northern North Sea are analysed for the occurrence of borehole failures are observed, abundant drilling-induced fractures are detercted in all of the image logs in wells to the east of the graben. Also the orientationof S_H appears to be slightly different for the western and the eastern part of the investigated area. An S_H orientation of approximately N100 deg-E is found in the western part, while the S_H orientation is found to be approximately N80deg_E for the wells in the eastern part. Investigating the conditions for fracture initiation in three of the wells alows to constrain the possible magnitude of S_H, For all three wells the occurrence of drilling-induced fractures can only be explained if the S_H magnitude is at least slightly greater than the vertical stress, which indicates a strike-slip tectonic regime (S_h