Oil and gas in the North Aegean
The only Greek oil and gas deposit in the North Aegean that has been produced to date was opened up in the Prinos Rift Valley between the Macedonian mainland and the opposite island of Thasos .
Prinos deposit
The block tectonic Nestos-Prinos Basin formed during the Alpidian orogeny lies at the south-eastern end of the Rhodope massif. It covers about 800 square kilometers. Several steeply dipping and powerful north-east-south-west major faults and numerous parallel trending, staggered, south-west dipping north-west-south-east faults form the break basin. It extends from the Nestos Delta in the north to the Kavala Threshold in the south with a length of about 38 kilometers and a width of up to 20 kilometers. It is divided into two sub-basins, the Nestos Basin in the northeast with a depth of up to 3950 meters and the Prinos Basin in the southwest of around 5500 meters. The two sub-basins are separated by a basin sill in the area of the Ammodhis field. The lowering of the fracture area continues to this day.
With the rapid tectonic collapse of the rift in the middle Miocene, the entry of the pre-evaporite series with thick sediment sequences from the erosion of the surrounding northeast and southwest land mass began. It is coarse clastic basement rock as well as sandstone, claystone and coal. The latest in this series has a marine character and consists mainly of slates with sandstone layers in between. This is followed by a zone with limestone, dolomite and anhydrite layers in alternating layers with clastic material that is present in the southern part of the Prinos sub-basin. Over the entire southern sub-basin, the uppermost layer is dominated by an extensive layer of dark gray claystone. The Prinos sediments in the south trough reach a total thickness of over 2000 meters.
With the marine claystones of the Middle to Upper Miocene, enormous amounts of organic components were introduced, especially foraminifera , nanoplankton and algae . During its rapid subsidence, the steep relief of the basin led to an extensive and up to 300 meters thick deposit of turbidites , which brought in considerable amounts of plankton with the finest sediment components. In the deepest central part of the basin, the organic components were converted into hydrocarbons under highly reducing conditions, high pressure and high temperature , which finally migrated from the bedrock to the higher-lying peripheral storage rocks. The migration ended, as a result of the salt cover in the hanging wall of the series, in anticlines and overturned bedrocks in front of the northwest-southeast-trending faults, such as in the Prinos and Prinos-Nord oil fields or in front of the southwest end of the sinking trough in the squeezed-up natural gas field Kavala-Süd. In addition to other tectonic and stratigraphic traps, the Kalirachi trap is a specialty: It was created by the intersection of two steeply falling syngeneic disturbances.
In the first sedimentation phases, the entire basin was completely flooded. The Mediterranean was connected to the Atlantic via the Strait of Gibraltar. In the last phase of the Miocene, at the end of the Messins, about five to six million years ago, the Mediterranean was cut off from the Atlantic by tectonic uplifts in the Gibraltar area. The Messinian salinity crisis set in , the drying up of most of the Mediterranean Sea. The Kavala threshold between the island of Thasos and the opposite mainland began to rise, turning the basin into a lagoon. Such a threshold was also created on the northeast side of Thasopoula. During this time, a whole system of such closed basins has formed in the North Aegean in addition to the general drying out.
Under the messinic conditions, overlying the Prinos sediments, the evaporite series with thick salt layers was created, characterized by two different deposition sequences : in the northern Nestos basin three to five meters thick layers of anhydrite and limestone alternating with sandstones, clay stones and marl, in the southern Prinos Basins alternate - with increasing thickness towards the center of the basin - seven to eight salt layers with clastic sediments . This suggests that several periods of drought and flooding occurred. The salt is white to gray, crystalline and often grown together with anhydrite, layers of anhydrite and dolomite occur alternately. The entire thickness of this series reaches up to 800 meters in the basin.
The continuously clastic post-evaporite series was created in the Pliocene and Quaternary when the terrestrial mountains were eroded and today extends to a water depth of 30 to 50 meters in the shelf area between Loutra Eleutheron on the mainland and Skala Marion on Thasos. It is characterized by a high content of organic material and indicates a deltaic deposit on the hanging wall through coarse-clastic sediments with a rich proportion of mollusc remains. Marine, clastic sediments are in turn overlying these deposits. The thickness of this series is up to over 2000 meters.
Oil and gas production
At the beginning of the 1970s , the prospecting for crude oil on the North Aegean shelf, which stretches from Mount Athos to the Greek-Turkish border , was awarded to an international consortium with the American main shareholder Oceanic . Co-shareholders were Colorado , Fluor Corporation and White Shield . The German Wintershall AG later took over the Colorado shares. In the years 1970 to 1973, the consortium was able to achieve initial successes west of Thasos with seismic surveys and exploration drilling in the Thracian Shelf Sea. Two deposits were discovered at depths of 2,490 and 2,770 meters, the Kavala-Süd natural gas deposit and the Prinos oil deposit . The majority of the quarry basin lies offshore between the island of Thasos in the east and the mainland at Perama in the west. Only the north-eastern part of the basin is onshore in the level of the Nestos Delta. The total area of the basin is 800 square kilometers. The sea depth is less than 50 meters.
In the aftermath of the world oil crisis of 1973 and based on the promising results from the first investigations, the government of Greece felt compelled to found the state-owned Public Petroleum Corporation (PPC) in 1975 . This company took control of all exploration and drilling activities, as well as oil and gas production in Greece, the import of crude oil and the operation of oil refineries. At the same time, international oil companies received special incentives for the development of the oil and gas deposits .
The international consortium North Aegean Oil Company (NAPC) was founded in 1976 under the leadership of the Canadian Denison Mines Ltd., Toronto, with a stake of 68.75 percent. The remaining shareholders were Wintershall AG., (12.5 percent), Hellenic Oil , subsidiary of Fluor Corporation , Irvine, California / USA, (10 percent), and White Shield, subsidiary of Basix Corporation, New York (8, 75 percent). Denison Mines finally took over all partner shares in 1979 and began with the two concessions Prinos and Kavala-Süd with the preparatory work for the development of the deposits by the construction of two production and one service platform on the oil deposit Prinos and one production platform on the natural gas deposit Kavala-Süd. After the completion of the platforms, which were set up at a depth of around 30 meters, the first production wells were drilled. One underwater pipeline each for oil and gas was laid from the platforms to the refinery in Nea Karvali . Since the Prinos petroleum contains large amounts of harmful, dissolved hydrogen sulfide (H 2 S), this gas is removed in the refinery process and crude oil, condensate and sulfur are produced. Part of the natural gas from Kavala-Süd is used in its own area for electricity generation, the rest is fed into the local gas network after cleaning. The investment costs should have been 600 million US dollars.
Oil production started at 8,000 to 10,000 barrels a day (bpd) at the beginning of 1981 and peaked at more than 30,000 bpd in 1989, which corresponded to almost 13 percent of Greek demand. Total oil production up to the end of 1995 was 92 million barrels. Natural gas production from Kavala-Süd amounted to 1,750 trillion cubic meters by the end of 1995. With ongoing exploration, the Prinos Nord oil deposit was discovered in 1994. From 1996 the additional oil production from this field caused the production to increase again for a short time. However, it declined to 9,000 bpd and eventually to 6,000 bpd during 1996 due to depletion of the main Prinos deposit.
The NAPC ultimately intended to develop and exploit the supposedly large deposits east of Thasos, which Oceanic had already explored through geophysics and exploration drilling in the 1970s . However, the Greek government banned any activity there because of border disputes with Turkey. A small area of the concession lies outside Greek territorial waters, albeit within the Greek continental shelf. Since the oil price had also fallen and there was no support from the PPC, the NAPC ceased operations in 1997/1998 and transferred the entire operation to the state.
At the end of 1999, the Greek government signed a five-year contract with Kavala Oil SA, which included the transfer of the concession, all offshore facilities and the refinery. Operations continued with a delivery rate of 3000 bpd. The majority of this company, 67 percent, was owned by the local private Evrotechniki SA, while the remaining 33 percent was held by the factory union of the former NAPC. The products were sold to the state-owned Hellenic Petroleum (HP), the successor company founded in 1998 and now 41.5 percent privatized. On a modest scale, new exploration work was carried out by Kavala Oil; Laterally deflected directional boreholes were drilled primarily within the existing boreholes in the Prinos fields. In 2001 and 2002 these gave indications that further oil reserves are available in the area of the Prinos basin. As a result, a new partner was won for Kavala Oil in October 2003. The British Regal Petroleum, London, took over 86 percent of Evrotechniki SA, corresponding to 58 percent of the company.
At the end of 2003 and in January 2004, Kavala Oil SA discovered a new oil field within the Prinos Basin, three nautical miles west of Kalirachi, in the tectonic Kalirachi trap with the Kalirachi 1 well, which, according to the operating geologists, was 227 million barrels Oil should lead, which would have corresponded roughly to the exploited Prinos reserves. Around 50 to 80 million US dollars should be invested in a production of 40,000 to 50,000 bpd. The reserves on the continental shelf east of Thasos were 900 million. Barrel estimated, which should increase the output from the North Aegean area to more than 200,000 bpd.
Probably based on these assessments, Regal Petroleum increased its stake in Kavala Oil SA in August 2004 and January 2005 to 95 percent. After drilling the Kalirachi 2 well in June 2005, however, it became clear that the field could not be exploited economically due to insufficient bedrock permeability. The stocks have been reduced to 30 percent of the estimates. Oil production in the first nine months of 2005 was only 2200 bpd. In September 2005, Regal Petroleum announced that it would withdraw from the Prinos field operation. Since then, in agreement with the Greek government, Regal Petroleum has been the main shareholder of the company, but has handed over the entire management of the oil fields and the refinery to the union and is no longer willing to support the company financially. Under the new leadership, production dropped to around 1600 bpd in 2005.
By the end of 2004, a total of 29 wells had been drilled in the shelf west and east of Thasos, 21 of which were production wells, from which around 103 million barrels of oil were produced. At the end of 2004, oil reserves in Prinos, Prinos-Nord and Epsilon amounted to 22 million barrels, of which 7 million are certain and 15 million are probable. The significant Epsilon deposit was discovered in 2003, but was neglected at the time because of Kalirachi. New platforms on Epsilon and the connection to the Prinos network would require an investment of 50 to 60 million euros for a funding of 5000 bpd. Regal Petroleum's role in this project and the company as a whole remains uncertain to this day.
Negotiations between the Greek and Turkish governments began as early as March 2002 on the decades-long differences over the North Aegean sea borders. A result is still not available.