Tengiz Field - Geology

Geology

The oil reservoir at Tengiz occupies an immense build-up of limestone, essentially a large atoll or reef built on the margin of the deep North Caspian Basin. The atoll was built by marine organisms such as corals and stromatoporoids, mostly during Carboniferous time, but some reef-building probably occurred earlier during the Devonian Period as well as later during the Permian. The reservoir is sealed by thick, impermeable Kungurian salt of Permian age.