The Bahar oil and gas-condensate field in the South Caspian Basin

The Bahar Field was discovered in 1968 and contains oil and gas-condensate in sandstones and sandy siltstones belonging to the middle Pliocene Productive Series. This has a total thickness of 3600 m. It consists of alternating sandstones, sandy siltstones and shales, with thicknesses between 5 m and 50 m and is of deltaic origin. The reservoir rocks have porosities of 13-18% and permeabilities of 45-250 mD. Biomarker geochemical analyses of onshore and offshore fields show that the Pliocene oil and gas fields in the South Caspian Basin have been charged primarily from epigenetic hydrocarbons. The hydrocarbons have migrated vertically along faults from older source rocks, probably including organic-rich shales of Oligocene to early Miocene age. The Bahar Field is quite mature. Of the original hydrocarbons in place, 72% of the gas has been produced, 39% of the condensate and 11% of the oil. The main oil-bearing horizons, the Pereriv Suite (SP) and Balakhany X, are developed with reservoir pressure maintenance by longitudinal and marginal (up-dip) flooding of surfactant-added sea water.