Hydrocarbon exploration in carbonate and shale deposits seems to be less efficient than exploration of terrigenous reservoirs in the Timan-Pechora Basin. This disparity is due to a number of factors, chief of which are complexity of geological structure in areas of carbonate and shale reservoirs and complexity and unpredictability of porosity and permeability. Therefore, considerable heterogeneity of carbonate and shale reservoirs reduces efficiency of prospecting, exploration and engineering of oil deposits in carbonate reservoirs.
The study of carbonate and shale reservoirs, which formed in different periods in the Timan-Pechora Basin, has highlighted importance of tectonic fractures in the evolution of complex reservoirs. These fractures are formed during local tectonic folding. The pervasive faults and fractures generated during these folding episodes in carbonate and shale rocks promote active filtration and leaching by surface and subsurface waters, containing corrosive components (CO2, H2S, etc.). Highly permeable fracture zones, which are called sweet spots, affect the processes of hydrocarbon migration and oil-gas accumulation. Exploitation experience at Usinsk, Kharyaga, Upper Vozey and other oil fields has shown, that sweet spots influence processes of oil pool formation. It is necessary to take into consideration such sweet spots when the optimal system of reservoir engineering is chosen. An integrated exploration method has been developed for finding and delineation of sweet spots. This method includes analisys of seismic and gravity exploration data, aero-space photo-interpretation, well logging data, results of core and drilling data interpretation.
The use of integrated exploration is proven to be effective in finding sweet spots in carbonate and shale reservoirs. It has also enabled greater understanding of the complexities, geometry, and tectonic relationships of sweet spots formation.