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Stress Field and Fracture Analysis of Paleocene Rock Unit Using Borehole Image Data and 3-D Seismic Interpretation of Kohat Foreland Basin, Pakistan

Abstract

The Kohat Foreland Basin located in Upper Indus Basin, Pakistan and considered to be the south western extension of Himalayas. Tectonically, KFB (Kohat Foreland Basin) is bounded by MBT (Main Boundary Thrust) and Kurram Fault in the north and west respectively. While in the south east, right lateral Kalabagh Fault lies which terminates the WSW-trending Salt Range at its southern end. The area had been influenced by the southward progression of deformation during late Miocene. Results of updated 3D seismic interpretation integrated with borehole image data from six different wells are presented. Our aim is to interpret the sub-surface structural geometry and to analyze the fracture pattern and stress rotation (σhmax) in the study area. The results of seismic interpretation show thrust related geometries in the study area which reveals that the area underwent NS directed compressional tectonic force in late Miocene. The results of borehole image data from six were plotted on Rose diagram (Dip and strike) to present the stress orientation and breakout analysis. The results show very dense to moderate dense fracturing pattern in well three well while less dense in two wells at Paleocene level. Most of the fractures developed in response of maximum stress direction i.e. NNE-SSW while the borehole breakout data indicate NE-SW to ENE-WSW direction. The rotation of (σhmax) indicates change in strike of the compressive structures from EW to NNE-SSW. It is proposed purpose that the compressive structures i.e. folds and faults developed earlier are rotated and oriented in NE-SW direction due to strike-slip transpressive movement in later stage. This strike-slip related movement could be related to Kalabagh fault located in the south east of the study area. It is also suggested that the rotation of maximum principal stress (σhmax) in the north eastern part of the study area could also be caused by transpressive movement which might be the segment of right lateral strike-slip fault system.