Modeling of a carbonate reservoir of ultraviscous oil of the Kazanian Stage to determine priority areas for development

The presented analysis of the three-dimensional geological model of the Gorsky ultraviscous oil reservoir, located on the eastern side of the Melekess Depression (the border of the Republic of Tatarstan and the Samara region). The main productive proposals are relict-organogenic calcareous dolomite and oolitic calcareous dolomite of the Kazanian Stage. The geological model of the Gorsky reservoir included three models: lithologic-facies and petrophysical models and a saturation model. A lithofacies model, created to determine the nature of the spatial distribution of organogenic, oolitic and other marine formations, was used to reconstruct the paleogeographic sedimentation environment and showed that the stratigraphic sequence of carbonate sedimentation is represented in the form of eight stages. The purpose of constructing a petrophysical model and a saturation model was to determine priority directions for the development of the carbonate reservoir of ultraviscous oil of the Kazanian Stage. The authors assessed the oil-saturated volumes of rocks that have standard oil saturation within the main lithotypes. The share of relict-organogenic dolomite accounts for 60 % of the oil-saturated volume of rocks, and the share of oolitic dolomite – 40 %. Despite the fact that relict-organogenic dolomite is more oil-productive, it has worse reservoir properties. For the development of the Gorsky ultraviscous oil deposit, the priority areas are areas with improved petrophysical characteristics and a high oil saturation coefficient in combination with the use of steam-heat methods.