Undiscovered Potential in North Oman's Subtle Natih Truncation Traps

Abstract

Abstract The Cretaceous age Natih truncation play in northern Oman is an underexplored play due to the challenges of finding subtle traps. Key elements include two angular unconformities occurring in north Oman that contribute to the complexities of the truncation trap. The Turonian unconformity subcrops the Wasia Group under the overlying Fiqa shale of the Aruma Group. The Base Cenozoic unconformity not only erodes the Aruma, but also the Wasia Group at a higher angle than the Turonian unconformity. Both groups truncate roughly toward the west/southwest, and the area with the most Natih truncation potential is the area in which Natih is overlain by the Cenozoic. As the two unconformities merge, seismic multiples from the younger Hadhramaut Group distort the seismic imaging of the unconformities due to the absent Aruma Group. Lastly, variations in the Natih facies also cause complexity due to differing impedance contrasts between the lower Hadhramaut and the upper Wasia Group. For proper lead identification, the difficulties in the seismic imaging, seismic interpretation, and well top interpretation need to be accounted for and addressed. The simplest and most cost-effective way to tackle this problem was to use the most current seismic volume to create a variety of filtered volumes and angle stacks. These volumes were used to understand which reflectors could be considered robust and which are influenced by multiples. Depending on the area, the deeper Natih reflectors were determined to be the most representative of the Natih trend. In areas of more truncation, the deeper Shuaiba formation reflector was a more suitable guide. An extensive study of the well tops in areas with dense well penetrations was conducted to understand the thickness variations and ranges between the individual Natih units’ reservoir-seal pairs. These thicknesses were integrated with the seismic data to create the geologic model and quantify the uncertainty. The final model represents a series of high-resolution reservoir-seal pairs and their expected areas of truncation. The result of this project was a detailed model incorporating well tops, seismic horizon and fault interpretations, and isopach guidance. This model was used to identify where reservoirs are truncating against the top seal, how quickly the reservoir gains thickness away from the truncation, the thickness of the base/lateral seal, and probable juxtapositions across faults. The information gained can then be used to prioritize areas with more truncation potential. Bypassed Natih pay in previous penetrations can now be attributed to a truncation trap. And more importantly, new prospects can be matured with larger prospective areas and volumes due to the understanding of the stratigraphic trapping mechanism. As of 2023, several new truncation trap fields have been discovered, and many more prospects await testing. This modeling technique can be applied to similar truncation opportunities locally and worldwide.