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Thick successions of Cretaceous carbonates in the southern Apennines of Italy are of great economic interest since they host important aquifers and huge hydrocarbon accumulations. The reservoir of the Val d???Agri and Tempa Rossa oilfields (in the subsurface of Basilicata) consists of Upper Cretaceous rudist-rich lime- stones passing downward into mid-Cretaceous dolomitized limestones of restricted platform facies. Upper Albian- Lower Cenomanian dolomitized carbonates exposed in the Sorrento Peninsula and in the Cilento Promontory, part of the Apennine Carbonate Platform, represent a good surface analogue for the lower part of the reservoir. They are composed of meter-thick beds of stratabound dolomite and shallowing-upward cycles of restricted platform limestones capped by silicified evaporites and marly levels. Field relations, petrography, and geochemistry implicate the reflux of penesaline waters as the most probable dolomi- tization process. High-frequency climatic variability between dry and wet phases can explain the formation of evaporites, which are coeval with karstic bauxites in other sectors of the southern Apennines. The dolomitized car- bonates of the Sorrento Peninsula pass laterally into do- lomitized breccias, which were the result of local tectonic collapse of the platform. This is further evidence of mid- Cretaceous syn-sedimentary tectonics that in other areas of the Adria passive margin contributed to the formation of intraplatform basins where source rocks accumulated

Carbonate reservoirs from the Lower Cretaceous Thamama Group are of major economic interest since they host some of the largest hydrocarbon accumulations in the United Arab Emirates. This study focuses on a Thamama reservoir from the Kharaib Formation and aims at complementing the regional geological understanding through the integration of newly cored and historical wells. The reservoir of interest consists of a thick organic and clay-rich dense zone at its base characterised by mud-supported, discoidal orbitolinid-rich deposits. This interpreted mid-ramp dense succession is overlain by a thick reservoir unit deposited under inner ramp environments, hence describing a large-scale shoaling trend. In detail, the reservoir succession records higher hydrodynamic conditions than the dense unit, as testified by the predominance of grain-supported textures (from packstone to grainstone). Floatstone to rudstone interbeds with grainy matrices are associated with Lithocodium/Bacinella- and rudist-rich accumulations mainly recorded in the lower and upper parts of the reservoir, respectively. A series of depositional cycles of regional significance have been recognised throughout the reservoir succession and are usually bounded by prominent stylolites, correlatable across the field. The reservoir succession is predominantly characterised by micropores, although macropores (especially vugs) also have an important contribution to the pore system. The extent and impact of dissolution is highly variable, but overall, it is responsible for the creation of most macropores (ie. secondary macropores are more abundant than primary macropores). Subsequent to dissolution, the pore system is typically heavily degraded by cementation from non-ferroan calcite cements and, to a lesser extent, by dolomite cements. An emphasis has also been put on recognising the residual hydrocarbon, the abundance of which varies considerably at field scale. To better constrain the vertical and lateral distribution of the reservoir heterogeneities, nineteen layers of interest depicting the main reservoir quality trends have been interpreted. The creation of comprehensive sets of maps – consisting of sedimentological, thickness, diagenetic and hydrocarbon staining maps – for each of these layers allowed a high-resolution understanding of the reservoir architecture. Of interest is the upward increase in reservoir quality reported towards the upper part of the reservoir unit, associated with the development of thick rudist-rich intervals, which favour the development of a macropore-dominated pore system facilitating fluid flow. By contrast, the common presence of stylolites plays a key role in the creation of baffles or barriers throughout the entire reservoir. This integrated approach has allowed a better prediction of flow units at field scale and provided valuable input data for future reservoir modelling.

The interpretation of depositional environments following sedimentological description is one of the most fundamental steps for the understanding of the vertical and lateral lithofacies groups’ distribution. This is directly linked to sequence stratigraphy and reservoir quality heterogeneity. Despite its importance, many interpretative lithofacies association schemes fail to capture, in a clear, systematic and flexible way, the key environmental features affecting the depositional fabrics’ distribution and their associated reservoir quality. This is especially true in carbonate systems, where the reservoir quality evaluation is complicated by the deep interrelation between physical (i.e. hydrodynamism) and biological processes. Our innovative depositional environment scheme (DE) comprises a variety of codes relating to key depositional and environmental characteristics in a way that captures their hierarchical organisation. These codes comprise groups of lithofacies interpreted to be genetically related, which provide metre-scale information commonly correlatable with wireline logs, that constitute ‘building blocks’ for static depositional architecture. The carbonate DE scheme is designed to be generic and flexible and therefore can be applied to any carbonate ramp, shelf or platform setting. The DE nomenclature uses an ‘initials-type’, letter-based abbreviation coding, which provides a straightforward and accessible understanding of the interpreted depositional environments. This comprises a suite of codes organised from a large to a small(er) scale using the formula: ‘1.2’. The first uppercase abbreviation code (1) defines the environmental belt and the energy level (i.e. hydrodynamism) from the continental to the deep offshore realm. Hydrodynamism abbreviations are typically appropriate for inner/proximal settings where a wide range of energy levels may occur.The second lowercase abbreviation code (2) corresponds to qualifiers that are used to highlight subtle variations in environmental conditions favouring the development of specific faunal assemblages (e.g. Lithocodium/Bacinella or rudists) or sedimentological features (e.g. clay content, lamination). These qualifiers allow a direct link to reservoir quality variations at the stage of sedimentological coding. Where specific geobodies can be interpreted within an environmental belt (e.g. an oolitic shoal in a dominantly high-energy inner/proximal setting) a code referring to the geobody can be added as a suffix in uppercase. The hierarchical organisation of this scheme is proven to be of great value for reservoir quality analysis. This is because it allows a simple and direct visualisation of the gross environmental settings on a carbonate platform, alongside its hydrodynamism (i.e. high-energy oolitic grainstones vs low-energy argillaceous-rich mudstones). Furthermore, the qualifiers capturing argillaceous content, allochem composition and/or depositional features are extremely effective to record reservoir quality heterogeneity and enhance sweet-spot prediction.