Structural inheritance through 3D reservoir modeling and ant-tracking attribute implications for structural configuration of Upper Cretaceous Pab Sandstone, Kirthar Fold Belt, Pakistan

Abstract

This research presents a comprehensive investigation to enhance understanding of subsurface structural complexities within the Upper Cretaceous Pab Sandstone reservoir level in a gas-producing field within the Kirthar Fold Belt of the Southern Indus Basin, Pakistan. The seismic interpretation for accurate structural delineation and characterization of intricate fault systems is often challenging in Fold and Thrust Belt settings. The 3D structural maps of Upper Cretaceous Pab Sandstone at the reservoir level and the application of the ant-tracking attribute for fault extraction improve the structural understanding of the gas-producing field in the Kirthar Fold Belt in the Southern Indus Basin, Pakistan. Attribute-assisted 3D seismic interpretation has revealed several subsurface structure elements, including a large thrusted anticline extended towards the north-south, the pattern of north-south oblique ramp thrusts on the southeastern flank, and a combination of easterly vergent thrusts with a counter-back thrust creating a local pop-up structure in the area. A 3D structural model at the reservoir level was generated using horizon and fault framework volume-based modeling approach, serving as a structural model for Pab sandstone. The structural smoothing, variance and ant-tracking attribute were applied iteratively to get the best results and correlated with manual interpretation. 3D seismic interpretation and application of ant-tracking for fault extraction identifies discrete structural styles and revealed that all thrusting occurred due to compressional tectonics of the Plio-Pleistocene period. The apparent different styles result from the reactivation of earlier extensional fault systems and probably during phased periods of compression. The resulting 3D reservoir model can be used as an input to populate petrophysical properties and results can be extended for future field development plans. Integration of well and 3D seismic data interpretation and the application of automatic fault extraction techniques are highly recommended in structurally complex areas and have an equal implication for worldwide basins with similar conditions for reliable structural interpretation in Fold and Thrust Belts with structural complexity.

Keywords

• Zamzama Gas Field
• Pab Sandstone
• Reservoir modeling
• Ant-tracking
• Structural complexity