Abstract: Subsalt complex of the Precaspian basin is rich in oil and gas resources. The discovery of a number of large oil-gas fields like Astrakhan, Tengiz, etc., indicates that the Mezhdurechensky block which is in the same structural belt also has relatively high hydrocarbon potentials. However, the subsalt complex in Mezhdurechensky block is under a great burial depth, so the favorable reservoir facies belt prediction becomes the key for hydrocarbon exploration in this area. This paper analyzes the regional structural evolution, compares with adjacent oil and gas fields and conducts the seismic facies analysis in order to predict the favorable reservoir facies belt. The result shows that Mezhdurechensky block experienced a similar tectonic evolution history with the sub-uplifts on the Astrakhan- Aktyubinsk structural belt, and paleotopography and the differential basement subsidence are the main controlling factors for formation such a facies belt, and the favorable reservoir facies belt of subsalt complex in Mezhdurechensky block are barrier reef carbonate rocks of Upper Devonian and Lower Carboniferous on the north and south sides of the block and grainstones of the Carboniferous on banks and shoals on top of the paleouplifts.

Key words: Precaspian basin, Mezhdurechensky block, subsalt complex, seismic facies, reservoir