The article considers factors influencing resistivity of rocks of volcanogenic-sedimentary sequence of the central zone of northeastern framing of the Krasnoleninsky arch. Dependencies for determination of oil saturation coefficient of volcanic rocks are proposed. Dependencies based on data of standard complex of well logging. As a result of the analysis of the electric dependencies (parameter of porosity from porosity coefficient, parameter of saturation from water saturation coefficient and the corresponding parameters of core samples) it is shown that the type of void space and post-igneous transformations have a significant influence on the value of the electrical resistance of the rocks of the studied sequence in addition to the composition of saturating fluids. With invariable values of porosity and water saturation coefficients, the increase of electrical resistance is characterized by cavernous and transformed under the action of the processes of albitization, carbonatization, silicification of rocks. The cracked type of voids, the presence of clay minerals contributes to the reduction of electrical resistance. Determination of oil saturation coefficient is performed using dependence of electric resistance obtained from well logging data on volume water saturation of core samples taken from wells according to insulating technology. The obtained dependence made it possible to detect excess of values of specific electrical resistance measured in wells relative to results of measurements on extracted samples of standard size for some intervals of studied sequence. The excess is characteristic of cavernous differences in volcanogenic rocks and albitized, carbonatized volcanites. In cavernous intervals, the excess is due to the influence of the scale effect, when standard small core samples do not fully characterize cavernous voids, the size of which can be comparable to their own. In albitised and carbonatized volcanites, the excess is due to a change in the initial type of wettability of core samples during extraction. At the same time, most of the rocks of the studied sequence are characterized by a hydrophilic type of wettability. Along with the considered factors, the obtained dependence takes into account the type of void space and post-magmatic transformations. The results of the calculation of the oil saturation coefficient are consistent with the results of direct determinations on the core selected using insulating technology. Application of the obtained dependence will make it possible to improve accuracy of reserves calculation and planning of geological and technological operations.
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