Innovative study complex of complexly structured hydrocarbon reservoir rocks, based on petrophysical and geochemical parameters (on the example of the Boryslav-Pokuttia zone of the Pre-Carpathian depression)

Abstract

The article examines methods of studying the capacity-filtration properties of reservoir rocks of hydrocarbon deposits and transformation processes and the state of kerogen depletion within the Boryslav-Pokuttia zone of the Pre-Сarpathian depression. The complex stressed state of rocks, which arises because of the action of geodynamic stresses, and the processes of catagenetic changes cause the development of secondary pore-crack and crack-cavernous reservoirs. Crack formation is caused by deformation and depends on the mechanical properties of rocks. The development of traps, pore-crack and crack-cavernous reservoirs is associated with rock loosening zones, which tend to tectonic disturbances and to places of intrusion of fluids from great depths into the sedimentary layer. At the same time, two multidirectional processes – thermal degradation and consolidation under the influence of pressure – cause changes that occur in the structure of kerogen during its evolution. Based on the results of the analysis of the actual and theoretical material, the optimal methodical set of studies of the most important characteristics of the reservoirs and the processes of kerogen evolution for the considered zone is substantiated. An analysis of the geological and petrophysical characteristics of the Oligocene deposits of the Inner Zone of the Pre-Carpathian Trough was carried out and database were formed. It has been established that pore-crack and crack reservoirs have a complex structure, and their distribution and capacity are controlled by two factors of different nature – lithological-facies and structural-deformation. It was found that thermodynamic modelling models – maximization of entropy and constants of independent chemical reactions – provide reliable results of the distribution of elements between the components of complex heterogeneous and homogeneous geochemical systems. It is shown that the chosen method of calculating the Gibbs energy of individual components of geochemical systems has sufficient accuracy for use in the above models.