The Middle-Triassic Gulailah Formation, also known as the Jilh Formation, was poorly understood in Abu Dhabi due to lack of data integration. A recent study involving mapping of the internal architecture of the formation on the basis of regional seismic data and all available wells across Abu Dhabi shows the evolution of an intra-shelf basin during deposition of the Gulailah Formation which was overlooked during previous studies. Interpretation of regional mud logs and updated isopach maps show a deepening trend from a shallow shelf in the northwestern offshore Abu Dhabi to a depo-center in the southern onshore. The isopach contours imply an increase in water-depth toward the basin center and mark the outline of the Gulailah intra-shelf basin as a restricted depression on the Middle-Triassic to Middle-Jurassic shallow-water carbonate shelf. The basin margin is characterized by a shallow-water shelf break, where the sudden change in slope leads to a higher thickness gradient. The regional variation of seismic reflection patterns from prograding and thickening events around the shelf-break to parallel reflections at the depo-center characterize the general geometry of the Gulailah intra-shelf basin from basin margin to basin center. Detailed well correlations based on GR cycles corresponding to 3rd-/4th-order sequences show a layer-cake model at the bottom followed by a prograding sequence towards the top of the Gulailah, representing the evolution from a gentle ramp to an intra-shelf basin.
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