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The Abu Dhabi coastline provides an ideal setting for the study of sedimentary systems inferred to be directly analogous to those which deposited many of the regions Mesozoic petroleum reservoirs. Improved understanding of these complex depositional environments, supported by quantitative sedimentological data, is essential to the development of accurate depositional models and reliable simulations for carbonate reservoirs. The arid southern shore of the Arabian Gulf has an extremely low-angle ramp geometry. The coast is locally protected from open marine conditions by a number of peninsulas and offshore shoals and islands. Sedimentary processes in the supratidal zone are dominated by the precipitation of evaporite minerals in the shallow sub-surface. A broad carbonate-evaporite intertidal setting, characterised by complex depositional facies geometries, passes off-shore, into a subtidal carbonate depositional environment. The coastline of the United Arab Emirates is currently undergoing massive infrastructure development at an unprecedented scale, with huge dredging and island-building projects changing the sedimentary dynamics of the coast beyond recognition. The impending loss of many of the natural coastal systems gives further impetus to the need for accurately recording these sedimentary environments before they are eradicated by the anthropogenic overprint. This study employs a range of analytical techniques to investigate and characterise the surface.

Abstract This paper aims to establish correlations between petrophysical properties, sedimentological, and diagenetic characteristics of carbonate rocks from well cores of the Lower Cretaceous Thamama Group. A previous petrophysical study by Saleh, et al (2008) on the same well cores revealed that four plug samples out of 17 have a strong anisotropy relation of shear velocity (Vs) and permeability. Based on these results, we conducted a thorough sedimentological and petrographical study to explain the unique characteristics of these samples. We performed a full 170 feet core description of a vertical well to study the lithological and diagenetic background of the seventeen samples. It was assured that the core plug samples represent all types of lithofacies observed in the core description. Thin sections from the samples were also prepared and described, and well log data were analyzed. The well core description resulted in the identification of five lithofacies: bioclastic wackestone with low cementation, Bacinella floatstone, requieniid rudist floatstone/rudstone, highly cemented orbitolinid wackestone/packstone, and thin bedded shale. Three out of four samples, that have Vs and permeability anisotropy relationship, belongs to the bioclastic wackestone. The fourth sample belongs to the requieniid rudist floatstone/rudstone. It contains dominant matrix and scattered requieniid rudist fragments. Thin section description showed that samples with anisotropy relation of shear velocity and permeability are characterized by: a pore system that is homogenously distributed (microporosity), without significant influence of cementation, abundance of allochems, and other type of porosities, abundance of matrix, lack of skeletal and non-skeletal allochems, and low cementation. On the other hand, samples that have no clear anisotropy relationship have abundant bioclasts are highly cemented and have dominant intraparticle, interparticle, vuggy, or channel porosity. Crossplot analysis of well logs and core description gave the following results:• Core horizontal permeability and porosity correlation has three main trends interpreted according to different degrees of cementation.• In general, as horizontal permeability of core increases, the compressional wave velocity decreases twice as much as the shear wave velocity, taking into account the preferential permeability direction.

The Lower Cretaceous (Aptian) Shu’aiba Formation is an important carbonate reservoir of the subsurface of Abu Dhabi. At an oil field located in northwest Abu Dhabi, the reservoir is comprised of interior platform, platform margin, clinoform belt (prograding wedges) and intra-shelf basin deposits. Sedimentologic and petrographic core description identified 12 lithofacies types, ranging from shallow-marine, rudist-rudstone to deep-marine, planktonic foraminifera wackestone and shale. Caprinids (Offneria sp.) dominate the Shu’aiba platform margin and the proximal clinoform belt. Algalstromatoporoid facies and caprotinid debris are indicative of the distal clinoform belt. Planktonic foraminifera wackestone and shales dominate the intra-shelf basin deposits (Bab Member). The Shu’aiba deposits at an oil field located in northwest Abu Dhabi fit well into the sequence stratigraphic framework established for a giant oil field of central Abu Dhabi. Shu’aiba transgressive and early highstand sequence sets are built by the Ap2 and Ap3 sequences, Shu’aiba late highstand sequence set comprises the Ap4 and Ap5 sequences, and the Bab lowstand sequence set is represented by the Ap6 sequence. However, the platform margin appears to be steeper in northwest Abu Dhabi, as the area of the Upper Aptian (Ap4 and Ap5 sequences) distal clinoform belt is narrower than the one encountered at central Abu Dhabi. Three-dimensional seismic analyses allow mapping of the platform to basin geometries. The areal extent of the interior platform, the platform margin, the clinoform belt, and the Bab Basin can be outlined by seismic cross-sections and seismic amplitude maps. All available data were successfully incorporated in a new 3-D static model, addressing uncertainties in terms of structure, stratigraphy, and reservoir quality.

Polygons have previously been described as ubiquitous features of the Abu Dhabi sabkha and coastline, yet there has been little effort to quantify these features or assess their preservation potential in the stratigraphic record. This study compared the morphology, mode of formation and preservation potential of evaporite polygons from the upper inter-tidal to supra-tidal zones with carbonate polygons from the lower inter-tidal zone of the Abu Dhabi coastline. Very large-scale peritidal polygons were identified as forming in hardgrounds over an extensive area of the peritidal environment. These polygons were sampled and their morphology was accurately mapped to produce a quantitative description of polygon characteristics and a genetic model for their formation. These polygons are interpreted to have developed through lateral expansion due to the growth of displacive calcite cements. In the upper inter-tidal zone a number of sites were defined (1 to 25 square meters) and regularly photographed and described to construct a graphic record of temporal changes in surface morphology. This study demonstrated that the upper intertidal zone is a dynamic sedimentary environment with many of the sabkha surface features in a constant state of flux. Meter-scale halite polygons formed as a result of the evaporation of surface and near-surface pore waters. The precipitation of salts resulted in lateral displacement and uplift of polygon margins as tepee structures. Uplifted margins are susceptible to aeolian abrasion and dissolution during humid summer months. Conversely, episodic winter rainfall ponds in dish-like polygon centers with consequent dissolution of salts to leave a residual rim tepee structure. During extended periods of rainfall total dissolution and removal of halite polygons may occur.