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<p>Fractures analysis is fundamental in constructing tectonic history and reservoir potential assessment of an area. However, fracture characterization is elusive in fold and thrust belts consequent to complex phases of tectonic deformation due to applied stresses. This paper explores the complex structure of the Lower Orakzai area using detailed fracture analysis, which is part of the hanging wall of the Main Boundary Thrust (MBT) present in Lesser Himalaya, Pakistan. The structural style of the study area is characterized by east-west trending tight to overturned folds and north dipping thrust faults that mimic the north-south Indian-Eurasian continental plate collision. Using circular inventory and rectangle inventory methods, fracture density was calculated, followed by calculating fracture porosity and permeability. Fracture analysis reveals that extensional fractures are oriented at high angle to the bedding and are trending in north-east, north-west and south-east directions, whereas the shear fracture form two conjugate sets trending north-east and north-west directions. The release fractures are oriented parallel to the strike of the bedding plane and trend in diverse directions e.g., north-east, south-east, north-west and south-west. The relationship between open fracture density and fracture porosity is uniform, while the relationship between open fracture density and fracture permeability is not uniform. Using the Naturally Fracture Reservoir (NFR) classification, qualitative analysis of the reservoir potential of each formation was conducted, indicating a range from Type-1 to Type-3 reservoir. Depending on the fracture system, the reservoir potential of each formation varies in descending order from Samana Suk Formation, Lockhart Formation, Shinawari Formation, Chichali Formation, Kawagarh Formation and Lumshiwal Formation. The maximum stress direction of 15 sampling stations lies in north-east, 8 stations lie in north-west while for the remaining 2 sampling stations, it lies in south-east, indicating the structural deformation is a result of north-south compressional stresses.</p>

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Fracture analysis and reservoir potential of Jurassic-Paleocene rocks exposed in lower Orakzai area, Lesser Himalayas, Pakistan

  • 期刊论文

  • 发表日期：

    2025年6月30日

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  • Wasif Ullah,
  • Syed Ali Turab,
  • Muhammad Awais Aziz,
  • Nasar Khan

摘要

Fractures analysis is fundamental in constructing tectonic history and reservoir potential assessment of an area. However, fracture characterization is elusive in fold and thrust belts consequent to complex phases of tectonic deformation due to applied stresses. This paper explores the complex structure of the Lower Orakzai area using detailed fracture analysis, which is part of the hanging wall of the Main Boundary Thrust (MBT) present in Lesser Himalaya, Pakistan. The structural style of the study area is characterized by east-west trending tight to overturned folds and north dipping thrust faults that mimic the north-south Indian-Eurasian continental plate collision. Using circular inventory and rectangle inventory methods, fracture density was calculated, followed by calculating fracture porosity and permeability. Fracture analysis reveals that extensional fractures are oriented at high angle to the bedding and are trending in north-east, north-west and south-east directions, whereas the shear fracture form two conjugate sets trending north-east and north-west directions. The release fractures are oriented parallel to the strike of the bedding plane and trend in diverse directions e.g., north-east, south-east, north-west and south-west. The relationship between open fracture density and fracture porosity is uniform, while the relationship between open fracture density and fracture permeability is not uniform. Using the Naturally Fracture Reservoir (NFR) classification, qualitative analysis of the reservoir potential of each formation was conducted, indicating a range from Type-1 to Type-3 reservoir. Depending on the fracture system, the reservoir potential of each formation varies in descending order from Samana Suk Formation, Lockhart Formation, Shinawari Formation, Chichali Formation, Kawagarh Formation and Lumshiwal Formation. The maximum stress direction of 15 sampling stations lies in north-east, 8 stations lie in north-west while for the remaining 2 sampling stations, it lies in south-east, indicating the structural deformation is a result of north-south compressional stresses.