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Rock typing is an essential step in carbonate reservoir characterization and geological model building for reservoir simulation. A static rock type is defined as "a rock unit characterized by similar depositional and digenetic processes resulting in a typical and unique Ø-K relationship and capillary pressure curve at given wettability. Reservoir representative rock types lead to a better understanding of reservoir fluid movement and oil recovery. This paper establishes a deterministic rock type scheme in a carbonate reservoir and presents a methodology to distribute these rock types vertically and laterally in the 3D geological model using wells data, conceptual model and reservoir structure map obtained from 3D seismic. Introduction The carbonate reservoir discussed here is a carbonate rudist build-up complex with large areal and vertical variations in petrographic and Petrophysical rock properties. An offshore Abu Dhabi field situated at the eastern edge of the intra-shelf basin during the deposition of the late Albian to early Turonian Mishrif formation. A total of 61 wells drilled in this field. Recently, a 3D seismic was acquired to map the field extensions and characterise the reservoir properties. Furthermore modern analogues and sequence stratigraphy tools are used to quantify this heterogeneity in terms of rock types and distributing them in the reservoir. Rock typing is means of classifying the foremost rock properties which control matrix fluid flow into similar groups. The tools used for this purpose are petrographical description (rock fabric, pore type) and petrophysical measurements (helium porosity, air permeability, mercury pore throat size distribution and capillary pressure). Once the rock types are defined, an intgreated workflow was used to populate these rock types laterally based on wells data and the conceptual model of the Mishrif formation in this reservoir that was build using recent analogues, outcrops data and sub-surfaces field data. Workflows The workflow used in this study is summarized as follows figure-1:Classify each lithofacies and its association based on macro and micro scale (grain size, type and sorting etc).Identify pore geometry (pore type and size).Identify diagenetic alteration such as dissolution and cementation.Pinpoint each lithofacies petrophysical characters based on porosity and permeability relationship for a better definition.Rock typing scheme: Carry out grouping of similar lithofacies with similar petrophysical characters.Validation by pore throat size distribution (MICP)Validation by capillary pressure.Build the conceptual model based on outcrop/recent analogue and seismic to understand the lateral distribution of lithofacies. Mishrif Conceptual Model: The conceptual model of reef buildup growth is proposed to give a comprehensive understanding on how the Mishrif cycles and associated progradational, aggredational and retrogradational of reef complex sediments took place in this field taking into consideration the following:Modern carbonate analogues.Sequence Stratigraphy.3D seismic observations.

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Seismic reservoir characterization is commonly conducted after seismic acquisition and processing projects to support the following static/dynamic modeling. In general, such study for carbonate reservoir has high difficulty to evaluate fluid saturation or formation pressure change due to the stiffer matrix of carbonate rock than siliciclastic reservoir. Therefore, porosity prediction through seismic AI inversion tends to be solely applied owing to a clear correlation between porosity and AI. However, the field had experienced water/gas injection as well as oil production as at the 3D survey acquisition; hence the porosity map from the conventional AI inversion should be disturbed by these field development effects. Our workflow first involved rock physics analysis, AVO modeling in order to find out the correlation between the subsurface properties and the seismic response. AVO inversion was implemented and interpreted based on such fundamental steps. It resulted in delineating the quantitative behavior of gas/water injection and oil production schemes in Xp-p.p domain and generating the best seismic attributes to separate fluid saturation and pressure changes from porosity. These attributes are of value to interpret the spatial pattern of field development activities and to refine the porosity prediction.

Summary Reservoir zonation in a prominent offshore Abu Dhabi oil-field has been investigated by means of seismic sequence stratigraphy. The field is producing from a Rudist reef complex where only discrete zones yield high production rates. An advanced seismic sequence stratigraphy study was conducted with the objective to refine the interpretation and understanding of the extent and thickness variation of the producing zones to optimize further development of the field. This paper presents the methodology and results of a seismic sequence stratigraphic study using innovative technique for the extraction of chronostratigraphic relationships embedded in the seismic data. The underlying concept of the method used is that all stratigraphic events are detected and placed in stratigraphic order. These chronostratigraphic events or surfaces are generated at sub-seismic resolution and tracked throughout the seismic volume within the limits of user-determined bounding surfaces – picked horizons. The integrity of the results is supported by ties to wells and good consistence with a conceptual, traditionally accepted reef complex model.