Present-Day In-Situ Stresses in the Northeastern Zagros Suture Zone in the Kurdistan region of Iraq

The Zagros folded and thrust belt is among the earth's most active continental collision zones. The collision occurred in the late Oligocene-early Miocene, followed by continental shortening. The study area is in the Kurdistan Region of Iraq, including the northwestern extension of the Zagros suture zone. In this area, present-day stress data derived from actual measurements are rare. In the present study, the magnitudes and orientations of principal in-situ stresses were determined using well-logging data. Several wireline logs, including borehole image logs, conventional wireline logs, and six-arm caliper logs for two vertical wells provided detailed borehole breakout and drilling-induced tensile fracture (DITF) data between depths of 1600 and 2240 m. Two oil wells (wells A and B) were evaluated, and in well A, several breakouts occurred in eight distinct zones. The standard deviation of breakout azimuths was 11°, and the mean azimuth of the breakouts was N162°E. The orientations of the maximum and minimum horizontal stresses were determined, and the results were validated by lithological evaluation from wireline log data. The mean azimuth of maximum horizontal in-situ stress was N72°E, which showed relative consistency with the NE-SW to E-W direction of tectonic movement. Ultimately, the magnitudes of the three principal in-situ stresses were determined by two methods: poroelastic strain theory and breakout analysis. The stress regime below the depth of 1600 m was a reverse faulting stress regime, and above this depth, it likely changed to a strike-slip faulting stress regime. The results suggest that the pattern of present-day tectonic stress is controlled mainly by the collision between the Arabian and Eurasian plates.