Carbonate reservoirs form a specific microstructure of the void space of the rock due to their physicochemical properties, capability to fracturing, leaching and recrystallization. This microstructure is due to the Genesis of the rock and its reshaping during compaction and catagenesis. It includes micro-and macro-cracks and different forms of porosity and cavernosity. For the purpose of the carbonate deposit structure differentiating and assessing reserves, the ratio of the filtration properties of fractures and matrix is decisive. This relationship underlies the proposed classification of fractured reservoirs, including a purely fractured collector (tight matrix and fractures), a porous fractured type (low porosity matrix that feeds fractures) and a matrix reservoir type (filter matrix with a subordinate fracture distribution). The conditions and methods of diagnosis of the selected types are considered. Important condition for effective using of proposed classification of fractured carbonate reservoirs is analysis of tools and methods for characterization of reservoir types. Such methods include core analyzes with differentiated determination of capacity and filtration characteristics of fractures, computed tomography studies, well logs comparing initial and evaluations after exposure, particularly the methods of Radon Injection Logging. In complex studies performed in assessing reserves, it is effective to use the criteria for the minimum pore radius to determine the lower limit of the working matrix. An important condition for the effectiveness of such studies is the adoption of quantitative characteristics of selected types of reservoirs. This makes possible to diagnose types in the borehole sections, with further interpolation of them in the volume of the studied reservoir, and forming on this basis a typed model with a corresponding differential assessment of oil reserves.
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