oa Remaining Exploration Potential of the Paleozoic Section in Abu Dhabi

The pre-Khuff principal reservoir, Unayzah formation consists mainly of distal braid plain sandstones<br>with minor aeolian deposits. Facies controls on reservoir quality are weak. Quartz cement, Illite and<br>compaction are the main causes of reductions in reservoir quality in the Unayzah. Quartz cementation<br>tends to be most severe in the cleanest, coarsest sandstones and near certain fractures.<br>Paleozoic seals are provided by the Basal Khuff Clastics, tight basal Khuff carbonate and Middle Khuff<br>Anhydrite. The base Khuff carbonate seal does not appear to be regional extensive, but localised and<br>potentially prospect specific. However, there are insufficient data to accurately define the seal for the<br>Unayzah hydrocarbon accumulations.<br>The main challenge that faced the Paleozoic source evaluation and basin building was the presence of<br>few deep well penetrations. Therefore, much of the unknown source and tectonic information were<br>derived from the surrounding countries. This comes from understanding the regional tectonics and<br>depositional trends of the southeastern Arabian plate, which helped extrapolate the source trends into<br>the Abu Dhabi area.<br>The Silurian source rocks basin modeling was constructed to define the timing of hydrocarbon charge<br>from this source rocks. Also, the objective of this modeling was to gain an understanding of how the<br>Paleozoic hydrocarbon system works and, specifically, comparing the timing of hydrocarbon charge<br>with the timing of fields structural growth history. The basin modeling work of the Silurian Hot Shale<br>source rocks started by building an extensive database, which includes the information related to<br>source rock distribution, heat flow of the basin and the construction of the stratigraphic and the<br>lithological models. Additional inputs such as tectonic events and estimating the magnitude of the<br>removed section, during the erosional events, were added.<br>The current maturation modeling indicated that oil from Silurian source rocks was generated early in<br>the basin history and was widespread by the Late Triassic (220 Ma). Significant gas was present by<br>Lower Cretaceous (140 Ma) and dominated the hydrocarbon system by Middle Cretaceous (110 Ma).<br>Significant high mature gas was generated in the early Tertiary (50 Ma). At present-day, charge is still<br>active in the north of Abu Dhabi.