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Diagnostic Indexes of Reservoirs in Devonian Sediments of the Dnieper-Donets Depression

In the study of Devonian reservoirs of the Dnieper-Donets depression, there is greater interest in the sandy-silty and carbonate rocks and lesser interest in the pyroclastics and effusives. Toward clarification of the nature of the variation in reservoir properties of these rocks, studies were made on cores from 105 wells that penetrated the Devonian on 41 structures. Fracturing was studied on cores from 29 wells on 16 structures. Core recovery was very uneven - from 0.6 to 72%. Results of determinations of porosity, permeability, density, carbonate content, grain size, and parameters of fracturing on 3262 samples were treated statistically using a computer. A close relationship was found between open porosity m o and total porosity m Π and between density γ Π and open porosity for sandy-silty, carbonate, and volcanic rocks. In half the cases a relationship was observed between fracture porosity and density in carbonate and volcanic rocks and between open porosity and grain diameter, permeability k and porosity in sandy-silty rocks. See Table 1. Low coefficients of correlation between individual parameters indicates presence of other complicating relationships. For example, pore permeability is determined not only by porosity but also by the structure of the pore space. The lowest values of porosity at which rocks can have a pore permeability are: 5% for sandy-silty rocks, 4% for carbonates, and 8% for volcanics. Rocks with a pore permeability greater than 0.5 md under surface conditions retain filtration properties (0.2 md) at depths to 4000 m. Most (96%) of the carbonate rocks (589