oa Faults and Fractures in Carbonate Reservoirs: Khuff Formation of Arabian Peninsula

Several factors control the distribution of faults and fractures in reservoir rocks. These include the regional stress field, local strain due to the existence of larger structures, deformation history, presentday stress field, diagenetic changes, and mechanical stratigraphy. The regional stress field that affected the eastern part of the Arabian Plate since Permo-Triassic time involved extensional tectonics (leading to development of normal faults) during Permo-Triassic breakup of Gondwana and opening of NeoTethys as well as compressional tectonics (leading to folding, thrusting, and positive structural inversion) at later times (Coniacian to Recent). This stress history led to the development of fold traps (N-S asymmetric folds in east Arabia and NW-SE folds to the north and east). The local strain associated with the fold/fault structures led to the development of small-throw faults dissecting the fold traps as well as several sets of fractures in the Khuff and other reservoirs. Some of these fractures are related to the regional stress field and others are associated with the folds and/or fault-damage zones. Reactivation of the Permo-Triassic normal faults during later phases of compressional tectonics and development of N-S fault-propagation folds was probably associated with trishear deformation in the steep anticlinal flanks leading to additional fracturing of the rocks.