A Quantitative Assessment Method of the Productive Formation Wettability Indicator According to the Data of Geophysical Surveys

Abstract

Abstract The reservoir wettability nature should be taken into account while well logging conducting, reservoir engineering, methods of oil recovery enhancement and intensification selecting with the aim of residual oil reserves involvement into the development. In this respect, the development of a methodology for reservoirs’ wettability quantitative assessment on the basis of well logging data is very urgent and relevant. In this article, basing on the analysis of laboratory data on the wettability index and reservoir characteristics, a methodology for quantifying the wettability index from field geophysical data assesment has been developed, and the results of the method application in carbonate reservoirs of the Ural-Volga region are presented. For the first time, the analytical expressions between wettability and reservoir characteristics are obtained. It is shown that the formation wettability at its microlevel is determined by the average thickness of the residual water film on the filtration channels surface, and at the macrolevel – by the residual water saturation volume of the effective part of the productive strata void space. A methodology for wettability index by the residual reservoir water saturation volume quantitative assessment was worked out, and the necessary analytical expressions were obtained. The proposed methodology is as follows: –on the reservoir core samples collection in the laboratory environment, the following parameters are determined: wettability index, porosity, residual water saturation;–using the laboratory core studies data, the dependence diagram of the wettability index on the residual water saturation volume (volumetric moisture content) is plotted;–basing on the reservoir resistivity, determined by the prior to development geophysical studies, the residual water saturation volume of the formation is estimated and, using the graph, the wettability index is determined. The worked out wettability index quantitative assessment methodology has been successfully proven in the Ural-Volga region carbonate reservoirs. The method allows the wettability degree according to the geophysical data in every layer intersection assessment both in the cross-section and in the deposit area. The information about the reservoir nature and wettability degree will make it possible to proceed more rationally to the development analyzing, controlling, regulating and enhanced oil recovery methods engineering and, as a consequence, to reduce the risks of their practical implementation.