Oil has always been the dominant energy source in Turkish primary energy demand, which has increased steadily from 1965 to date. Throughout the 65 years of the upstream oil sector of Turkey, several national and international oil companies have operated, and more than one billion barrels of crude oil have been produced. The number of small-tiny fields is so numerous and scattered throughout the southeast region of Turkey due to several geological challenges. It is worth explicitly noting that the subsurface is extremely complex, and the occurrence of petroleum fluids is difficult to predict and describe. Technically robust and comprehensive definitions are the first necessary step in ensuring consistency of subsurface evaluations.
Exploration and production work in the Diyarbakır province of the south-eastern Anatolian Region has, for the most part, centered on Palaeozoic and Cretaceous petroleum systems. Over the past decade, national and foreign companies have considered the Diyarbakır province a high-return market with huge potential in exploration license areas, including the Palaeozoic conventional petroleum system, offering remarkable opportunities in Turkey.
Although the discovered accumulations have been smaller by size than most of the similar fields in the Middle East, about 80% of the petroleum in southeast Turkey is produced from Upper Cretaceous carbonates. In other parts of southeast Turkey, within the Diyarbakır region, the early Silurian sequence includes important source horizons, and oil discoveries have been made in Upper Ordovician sandstone (Palaeozoic petroleum system).
For a long time, petroleum exploration and oil production in the Diyarbakır Basin focused mainly on the northern Diyarbakır area, foothill belt, and eastern Batman area in the foreland basin whereas the middle and southern Diyarbakır Basin remained little known. Aladdin Middle East ("AME") has been the only company engaging in an exploration of hydrocarbons in the foreland Diyarbakır basin since the early 70'ies that resulted in the discovery of the Molla-Yasince Oil field in 1972 that produces Silurian sourced oil from a Cretaceous reservoir. A second foreland discovery was followed by Kastel that was drilled initially by Gulf Oil in 60'ies but thought to be dry; however, in 1990 Shell TPAO JV drilled a second well to make Kastel a discovery North of Molla-Yasince filed. In 2008, an AME-led consortium discovered oil in Arpatepe, the first commercially viable Palaeozoic oilfield discovered in SE Turkey. While most current Palaeozoic aged oil comes from Molla-Bismil fields, the biggest prospects for future production growth are from other Diyarbakır Basin fields, which are still relatively underdeveloped or unexplored.
The long-term picture that emerges from these exploration efforts includes a number of important achievements. Until the late 2007s, the prevailing view was that Upper Ordovician reservoir plays were restricted to small prospect fields in the southern foreland area. Exploration of Upper Ordovician reservoirs was ignited by discovering the Arpatepe Field by AME-led consortium in the southern Diyarbakır Basin in early 2008.
In south-eastern Turkey, national and independent companies have understood Palaeozoic plays in the Diyarbakır Basin. Despite the challenge of limited well and seismic datasets, evidence is growing for the Molla-Bismil region Ordovician-Silurian plays. Arpatepe, Bahar, Yeniev, and South Çalıktepe oilfields are some of the discoveries in this region. The notable first example was the oil discovered in the Bedinan sandstones by exploration well Arpatepe-1 in 2008. AME-led consortium proved that the oil was discovered in the uppermost Bedinan Formation in the Molla-Bismil area in Arpatepe-1 well, tested oil in the approximately 35 m, upper Bedinan quartz-rich sandstone member (upper B4), producing 350 stbopd (stock tank barrels oil per day) of a 40.90 degree API oil by natural flow. Another notable example was the oil discovered in the Bedinan sandstones by exploration well Bahar-1 in 2012 by Transatlantic Petroleum Company. Subsequently, several successful exploration wells (such as Altınakar wells, South Çalıktepe wells, Yeniev wells, and Çöltepe-1) were drilled to collect the required information to evaluate the commerciality and development feasibility of the field.
TPAO also has drilled several wells with positive results in the vicinity of Arpatepe discovery. The most recent is the Kılavuztepe-1 and Bağyaka-1 wells completed as oil producers in the Bedinan reservoir.
Another recent promising development in exploration license numbered M45-B with Salat-1 discovery. Announced by Çalık Petrol in February 2022, the well had hit a gross oil-bearing pay zone from the Bedinan Formation and flowed light, 42 degrees API oil of 1200 boepd.
These significant developments reveal that the deep-wells in the Molla-Bismil area is a Palaeozoic petroleum system. The exploration breakthrough in the Palaeozoic petroleum system, especially the Upper Ordovician-Silurian petroleum system in the Molla-Bismil oilfield, is inspirational for petroleum exploration in other provinces of south-eastern Turkey.
In a new exploration, the Upper Ordovician Bedinan-4 clastic reservoir on the Diyarbakır Basin plays great importance in the Molla-Bismil area. The discovery of significant oil fields in the northern and southern Molla-Bismil oilfields greatly enhances the petroleum potential of the Diyarbakır Basin exploration licenses with the approach of the new oil-producing fields and old oil-bearing pay zone (Bedinan sandstones). From the beginning of the first outstanding Paleozoic targeted studies by Aladdin Middle East Ltd. to the present become an important replacement of deep petroleum exploration potential in south-eastern Turkey. However, after more than 20 years of exploration, these sandstones are being penetrated by relatively deep wells. Reservoir quality, however, is variable and its prediction of importance for economic field development. Consequently, Turkey will increasingly rely on indigenous oil supplies from that region, at least until non-conventional oil enters the market in big volumes.