Assessment of collector properties of lower cretaceous sediments within the limits of eastern dipping of Stavropolsky bending fold of the central Pre-Caucasian region
Borders of complex shielding traps depend on the degree of certainty with which the area of rocks-collectors lithologic replacement is defined. In case of granular-type rocks-collectors the boundary of collector rock is defined by a reservoir clay content. Clay minerals in sedimentary rocks are normally present in a finely-dispersed state and have great specific surface, which adsorbs water molecules forming a layer of water with anomalous properties. Abnormal layers have a significant effect on physical properties of a clay collector, causing their difference from corresponding properties of a pure collector. Clay minerals contain chemically bound water in crystal lattice, radioactive elements in the lattice and those adsorbed on the surface. From these characteristics of clay minerals with a noticeable content of their manifold largely dependent Neutron properties and rock natural radioactivity essentially depend on the above-mentioned properties of clay minerals when their presence in a collector is rather high. Clay minerals, being present in a collector, due to the marked-above specific features have quite significant influence on collector properties and water saturation as well as on the nature of the correlations among geophysical, geological and calculating parameters. Information about clay content and porosity makes it possible to find out whether the reservoir rock is a collector while for a collector to estimate permeability, marginal effective porosity and bound water content. Data on clay provides correction of geophysical methods readings and correlation and dependences, taking into account the clay content of a collector, are used while determining coefficients of porosity and oil and gas saturation. Classification of Lower Cretaceous silt-to sand collectors of eastern dipping of Stavropol bending fold is justified to identify productive strata. Some criteria of collectors’ identification with account of boundary values of porosity and permeability are proposed.