Petroleum systems and hydrocarbon potential analysis of the northwestern Uralsk basin, NW Kazakhstan, by utilizing 3D basin modeling methods

Gas and minor oil production from the northwestern Uralsk basin is associated with TTGF, Çaganskaya and Darinskaya fields located along a NE–SW aligning chain of barrier reefs. Most important reservoir rocks of the basin are associated with shelf, reef, pinnacle reef, atoll and bar facies of the carbonate complex, deltaic or tidal facies of the platform deposits and clastic basinal fan or slope facies. The basin comprises multiple petroleum systems, characterized by deep marine black-shales of Paleozoic which shows up to 10% TOC. The evaluation of these petroleum systems were investigated by utilizing 1-D and 3-D basin models constructed using the geological, geophysical and geochemical data. The sub-salt section of the northwestern Uralsk basin demonstrates higher hydrocarbon potential and lower exploration risk compared to the post-salt sequence despite the necessity for drilling extreme depths (e.g. over 5000 m) particularly in the Inner Zone. Various traps associated with salt tectonics favor hydrocarbon accumulations in the Artinskian/Filippovskiy, Frasnian, Bobrikovskiy/Tulskiy and Bashkirian proven reservoir rocks. Among these reservoirs, the Artinskian/Filippovskiy is the major oil bearing reservoir rock particularly in the Teplovskaya, Gremiachinskaya and Teplovskaya fields. It has good hydrocarbon charge access to multiple source rocks. Besides, Kungurian salt forms efficient seal on the top. Among the 15 investigated and modeled source rocks, the most expulsive ones are Afoninskiy, Givetian, Famennian, Tournaisian, Tulskiy, Serpukhovian and Vereiskiy, which intensively charge reservoirs of the northwestern Uralsk basin starting from Triassic. Source to trap timing risk is minimal, particularly within the Inner and Escarpment zones since traps are older. Gas and oil generation, expulsion and migration model results point out a total of 179 Mboe gas and 89 Mbbl oil potential (subsurface conditions) associated with Gremiachinskaya, W. Teplovskaya, Teplovskaya, Tokarevskaya, E. Gremiachinskaya, Ulianovskaya and Tsyganovskaya structures.