The Impact of Kingri Strike slip Fault on the hydrocarbon Prospectivity of Eastern Sulaiman Fold Belt Basin, Pakistan

Abstract

The association of the Strike-slip phenomenon with folds and thrusts in the eastern Sulaiman foldbelt has been discussed for quite a long time by different researchers. This study emphasis on the impact of Kingri fault on the hydrocarbon prospectivity of the eastern sulaiman foldbelt. The structural elements of the study area are more convincing in explaining the intensity of the structural deformation on both sides of the Kingri fault that is to the west the intensity of the deformation is low and is structurally low as compare to the eastern side while on the eastern side large anticlinorium are found in the form of Fort Munroe and Zindapir, though these anticline are affected by wrenching but the surface geology depicts that there are no such big compartments made comparatively to the western side. The area is structurally high on the eastern side of the Kingri fault. Sub surface geology on seismic lines show that these anticlines are also affected by mega shear fractures. The overall observations suggest that the eastern side of the Kingri fault exhibits high topography, the structural folds are more elongated and tighter as compare to the western Sulaiman Lobe and the trends of the structural elements are almost N-S and the stress direction is almost east-west slightly oblique. This obliquity in the stress direction to the fold axis may have a great impact on the hydrocarbon prospectivity as it may make partitions in the structures at the reservoir level, though the Jurassic (Chiltan) and Triassic (Allozai formation) may act as potential reservoirs in the area but proper reservoir characterization and potential approach is required to validate the properties of the lateral seal which is also a major issue associated with strike-slip component in the area. The structural interpretation suggests that the eastern deformational front in the area is uplifted by high angle reverse faults, high angle back thrusts are also interpreted which suggests that the area has a pop-up structural geometry. To the east of the Kingri fault there are doubly plunging anticlines. The earth quake data suggest that both the western and eastern sides across the Kingri fault are affected by higher seismicity. Depths of the hypocenters are mostly 10 to 30 km which is a strong evidence of deep-seated active fault movements. Another approach was set to interpret the earth quake magnitude data with respect to the depth on both sides of the Kingri Fault to determine whether the Kingri fault is east dipping or west dipping. This has to be carried out regionally in order to analyze more data in a broad context. The average depth of the hypocenters on the western side was 35-40 kmv while on the eastern side the average depth was 15-20 km which indicates that the left-lateral Kingri fault is west dipping. Another difference in the structural style which was interpreted in this research was that the folds are West-Southwest verging to the west of the Kingri fault while on the eastern side of the Kingri fault the elongated folds are verging in the Eastern side or slightly South-eastern side. To the west of the Kingri fault is topographically and structurally low area, the structural trends are in NE-SW direction. The major stress direction in this area is southward as it may be partially marked as a part of the Sulaiman Lobe where the transport direction is towards south. The western part is highly deformed by extensive thrusting associated with strike-slip phenomena. Due to transpression, numbers of major anticlinal structures are sliced in to parts such as Miriwah Anticline has been sliced into three part i-e Miriwah, Northern Miriwah and Southern Miriwah Anticline. Though the seismic interpretation suggest that this area also gives us pop-up structural geometry. The main impact of the Kingri strike slip fault on the hydrocarbon prospectivity is that the associated fractures and minor faults with Kingri Fault cut across the fold axis obliquely that may affect the structures at the reservoir level such as Jurassic and Triassic reservoir. It may affect the porosity and permeability of the reservoirs. At some places the porosity and permeability may decrease and at some places it may increase as well. So for the exploration of hydrocarbons the structures in the area that may be productive must be scrutinized very carefully. Minor fractures and faults must be carefully studied on 3D seismic data to mitigate the risk factor at the highest level.