Lower Jurassic Tight Gas Exploration Potential in Offshore Abu Dhabi

Abstract

Abstract The Lower Jurassic, Izhara and Hamlah formations, evaluation study has been conducted to provide an understanding of the hydrocarbon exploration potential of these formations in offshore Abu Dhabi. This objective was accomplished by evaluating the data from legacy reports and analysis the available drilling and testing results of wells that were penetrating Izhara and Hamlah reservoirs. Also, the regional well log correlation, structural settings, lithofacies variations, depositional environment models, source rocks potential were incorporated into this study. These were resulted in better understanding of the facies variations, porosity development and hydrocarbon charge system. The timing of structural growth, the presence of indigenous source rocks, the hydrocarbon shows while drilling and the presence of high hydrocarbon saturation in the interpreted logs concluded that both the Izhara and Hamlah formations are hydrocarbon-bearing reservoirs. The Lower Jurassic section is comprised of sequences of shallow marine mixed carbonates intercalating with shale and anhydrite streaks. These formations, although exhibits a gradual thickening from the northwest towards the southeast direction, yet they show remarkable lateral consistency, both in lithology and log response. Primary and secondary porosity are generally moderate to poor in these formations, reflecting the deep burial compaction and reflecting the terrigenous shale and anhydrite nodules with the carbonate reservoirs. The Upper Izhara comprises of lime-mudstone and wackestone, cryptocrystalline, slightly argillaceous and occasionally dolomitic. This type of lithofacies is reflecting a similar depositional environment to that found in the Middle Jurassic Lower Araej formation, which characterized by low porosity and relatively high permeability. While, the Lower Izhara intervals is mainly comprised of shale with high hydrocarbon saturations and high porosity values. This lithology represents an unconventional potential for shale gas accumulation. The Hamlah Formation is comprised of a variety of carbonate lithologies that are characterized by relatively low permeability which, has been deteriorated due to the precipitation of minerals from the thin streaks of terrigenous shales and the anhydrite nodules. The evaluation of the Izhara and Hamlah formations resulted in defining high prospective areas for future exploration activities. The tightness of the reservoirs in these formations can be overcome by using multi-stage acid fracturing and long horizontal drain holes. This new technology will turn tight reservoirs of the Izhara and Hamlah formations into attractive targets for future exploration activities. The evaluation of reservoir properties, hydrocarbon charge system, trap development and seal integrity has resulted in defining significant hydrocarbon accumulations in the Izhara and Hamlah formations in most of the prominent offshore structures.