KURA BASIN

The Kura Basin is a northwest — southeast trending intermontane depression, which lies between the Greater and Lesser Caucasus mountains in east central Georgia. The basin is shaped by multiphase tectonism associated with the collision, accretion and rotation that took place between the main bounding plates of the Eastern European Platform and the Arabian Plate which began in the early Eocene and peaked in the Late Pliocene. In response to varying stress fields, several structural elements developed including thrust faults, normal faults, inverted grabens, strike–slip faults and associated structures. This tectonism has given rise to a host of structural traps within the basin which make it a very exciting basin in which to explore for oil and gas deposits.



Potential reservoir rocks in the Kura Basin are to be found in both Mesozoic and Tertiary age rocks. The main reservoir exploited to date in the Upper Kura Basin in Georgia is from the Middle Eocene sequence. The primary Middle Eocene reservoir, as in the case of the Samgori and Ninotsminda Fields, consists of tuffs, tuffaceous sandstones, tuffaceous breccia and carbonates. The average thickness of the reservoir in the Samgori area is of the order of 2,200 feet (670 metres). The most common reservoir type is fractured andesite–basalt tuffs which exhibit average effective porosity of 0.6% and permeability of 0.05 mD. The occurrence of any effective porosity may be principally dependent on the presence of fractures. The Samgori Field which was discovered in 1974 is Georgia's largest producing field and has produced 180 million barrels of oil to date with a peak production of 70,000 barrels of oil per day (bopd) in 1981.

The stratigraphy of the Upper Cretaceous in the Upper Kura Basin is known from limited deep drilling in the Samgori, Teleti, and West Rustavi Fields and more recently from CanArgo's Cretaceous oil discovery on the Manavi prospect together with surface outcrop. The upper part of the sequence consists of well–bedded fine–grained marine chalk and chalky limestones that resemble the fractured chalk reservoirs of northwest Europe (e.g. Ekofisk), the Arabian Gulf and Texas. High density open fracturing is observed in outcrop. Regionally this reservoir is similar to the prolific Cretaceous carbonate reservoirs of the North Caucasus where significant oil and gas condensate deposits exist in similar geology and are characterised by high well flow rates and high recovery factors. Wells in the North Caucasian oil fields such as Karabulak–Achaluk, Khiancort and Malkobek–Veznesensk typically produced at rates of 3,000 to 15,000 bopd with reported recovery factors of up to 50%, overall recoverable reserves were in the order of hundreds of millions of barrels of oil. Within the Kura Basin a well on the West Teleti structure, TLT12, tested gas at rates of up to 8.83 million cubic feet (250 MCM) per day from Paleocene and Upper Cretaceous carbonates in a sub–optimal test.

The primary hydrocarbon source for the Kura Basin is the regionally extensive Oligocene–Miocene Maikop shale. The unit can be up to 6,500 feet (approximately 2,000 metres) thick and have a total carbon content in excess of 10%. The rapid deposition of this interval resulted in high heating rates which led to the generation of sweet, low sulfur, 26° to 41°API crude oils with measured vitrinite reflectance values (Ro%) less than 0.7. As the axial part of the basin was buried to ever greater depths, the source rocks entered the gas generation window.