Using the combination of conventional logs, borehole image log, and six-arm caliper for determining the orientation and magnitude of principal in-situ stresses: A case study in Zagros suture zone in Kurdistan Region of Iraq

Abstract

Arabian and Eurasian plates collision zone is one of the active tectonic regions within the Middle East. The study area includes the northwestern extension of the Zagros suture zone. Due to the complex nature of geology and lack of reliable geomechanical data in this region, oil companies face drilling and production problems. As such, there is a great value in geomechanical study, and determination of orientation and magnitude of principal in-situ stresses has a vital role. The deepest drilled formation in this study is the Albian upper Qamchuqa Formation in northeastern Iraq which is a carbonate hydrocarbon reservoir. Based on the faulting system, the stress regime is varying between strike-slip and thrust fault. In this study, borehole image log and 6 arms caliper provided detailed information between 1490m to 2390m for breakout (BO) and drilling induced tensile fracture (DITF). Breakouts occur in 8 distinct zones and below the 1590m, a high number of BO with considerable length and also few DITF were observed in this well. Detected BO showed a relatively low standard deviation and varies from N10°W to N10°E. The orientation of maximum and minimum horizontal stress (σH,σh) was determined by BO and DITF and the results were validated by a 6 arm caliper and lithology evaluation. The average E-W direction of the σH shows relative consistency with the direction of NE-SW to E-W tectonic movement base on the world stress map in the nearby Zagros suture zone and also with earthquake focal mechanism solutions in a previous study in the nearby area. Eventually, the magnitude of vertical stress σv and σH, σh has been determined by the combination of the conventional log, total length, and width of BO.