About 115 million barrels of oil and 850 million cubic metres of natural gas have been produced from the Gulf of Kavala fields. Development of the Prinos oil field and South Kavala natural gas field commenced in 1979 and production started from both fields in 1981.The Prinos North field, located to the north west of Prinos, was brought into production in 1996 via a development well drilled from the Prinos platform.
Prinos Oil Field
Crude oil production commenced in Prinos in 1981 at initial rates of 8,000 BPD to 10,000 BPD and peaked at more than 27,500 BPD in 1985.
Currently, 11 producing wells and four injectors are active. The cumulative oil production at 31 December 2017 was 111,2 million barrels of oil.
The proven productive reservoirs in the Prinos Field, which lie at the depths of 2,490 metres to 2,790 metres TVDSS, occur at the top of the Pre-Evaporitic Sequence and comprise channel and distal fan turbidites created during the rapid subsidence of the basin during the Miocene Epoch.
3D seismic data shows the field, is formed by a low relief fault-bounded anticline situated on the southern down-thrown side of a major NNW-SSE trending listric fault. The anticlinal structure is dissected by a number of normal faults that are sub-parallel to the main listric fault.
The field is separated into four main compartments with 12 different layers, each with varying oil content. The field pressure ranges from 140 bars up to 400 bars, and the recovery of hydrocarbons is mainly achieved with the use of gas lift. The produced gas contains about 50% hydrogen sulfide. The reservoir reaches a depth of 2,500-2,800 metres, while the sea water depth in the area is 30 metres.
The oil produced from the Prinos oil field is an under-saturated sour crude with an API gravity of 27 to 30 degrees and a high sulphur content. The dissolved gas oil ratio (GOR) is ca 675 scf/stb, with a high H2S content in the gas ranging from 30 per cent in the B and C Sands to 60 per cent in the A Sands. The solution gas is processed onshore to remove the sour gas. The oil formation factor at initial conditions is 1.38 rb/stb and the bubble point pressure ranges from 1,175 to 2,045 psig. The in situ viscosity of the oil ranges from 0.55 to 0.8 cp at initial conditions, which gives a favourable mobility ratio under water flooding. The field was slightly over-pressured with an initial reservoir pressure of between 5,700 and 6,250 psia; however, current reservoir pressures reportedly range from 1,750 to 4,000 psia.
STOIIP is estimated at 302,7 mmbls.
Prinos North Oil Field
Prinos North comprises a similar reservoir with a STOIIP estimate of 24 mmbls. The single active well in the Prinos North field produced 313 stb/d sour crude oil in 2016 at an average water cut of 78 per cent. The cumulative oil production was 4,1 million barrels of oil stb, as of 31 December 2017.
The Prinos North oil field is a four-way dip closed structure separated from the Prinos field by a major listric fault that dips to the south. Part of the Prinos Group, the field contains hydrocarbons in Miocene stacked turbiditic sandstones.
The crest of the structure is at 2,100 metres TVDSS and the anticlinal structure is dissected by a number of minor faults; the most significant is a north to south trending fault with a variable throw of between zero and 300 metres. This fault gives rise to a downthrown western area with relatively low relief, penetrated by the three boreholes (two wells and one side-track), and an up-thrown eastern area that has yet to be drilled.
The oil from the Prinos North field is a moderate density, under-saturated sour crude, with an oil gravity of 21 degrees API. The crude oil contains about 7 per cent sulphur. The solution gas has a hydrogen sulphide content of 30 per cent and measured solution GOR is ca 300 scf/stb.
Epsilon Oil Field
The Epsilon oil field is an anticlinal structure some 3 km to the west-northwest of the Prinos oil field. Epsilon is a structural/stratigraphic closure formed from the confluence of two listric faults. It is located immediately to the west of the Prinos field and structurally separated by a shallow saddle. The trapping mechanism is structural/stratigraphic, with dip closure to the east and south, and reservoir pinch-out to the north and west.
The field was discovered in 2000 when Well E-1 tested sour crude oil with an API gravity of 36 degrees in reservoirs belonging to the Prinos Group at a depth of about 2,800 metres TVDSS. The well was side-tracked a year later to a location 500 metres to the south-east to confirm the reservoir presence and test oil.
Energean drilled an extended reach appraisal and development well from the Prinos platform in 2009-10. Two sub-horizontal legs were drilled into the reservoir. The well produced oil from January 2010 for a 12-month period, with an initial rate of over 2,000 stb/d. By the time a workover was undertaken in February 2011, when the casing was found to have collapsed, the oil rate had declined to 400 stb/d and the cumulative oil production was just over 0.3mmstb.
STOIIP is estimated at 45,1 mmbls.
The South Kavala Natural “Sweet” gas field was the first hydrocarbon reservoir discovered in the Prinos–Kavala Basin. It covers an area of 4 km2 and is located approximately 11 km south-west of Prinos Field in a water depth of 58 metres.
The field has been producing since 1981 and has produced more than 850 million m3. As is it is now 91 per cent depleted, South Kavala yields intermittent production at a rate of approximately 17,000 Nm3/day and 50-60 bbl of condensate oil for seven days a month.
Over 60 development wells have been drilled offshore, at an average depth of 3,000 metres, in the Prinos basin, where the company has been operating since 2007.
Since 2009, four jack-up rigs (Energy Exerter, Ensco 85, GSP Saturn and GSP Fortuna) have been mobilized to Greece. During the development stage of the Epsilon Field in 2010, an Extended Reach Drilling operation became the longest well drilled in the Mediterranean, with a length of 5,297 metres. In 2014, Energean purchased its own drilling rig, “Energean Force”, which has been operating in the Gulf of Kavala since May 2015, and provides the company with a cost-effective long-term drilling solution.
Energean has also drilled four wells onshore in Egypt.
Energean Force has been executing the biggest drilling programme in the history of Prinos and has already successfully drilled eight wells (among them an ERD) in Prinos.
The rig, which was bought from KC Deutag in 2014 (under the name Glen Esk) has undergone a full refurbishment in the Perama Shipyards, Greece. The rig has hull dimensions 321 ft. x 70 ft. x 34,5 ft and it is designed for water depth between 40 ft and 656 ft. while it can drill wells with a maximum depth of 20, 000 ft.
It has an 8 anchors mooring system, a hoisting capacity of 1000 kips and 2000 HP draw works and it is able to accommodate 116 persons. It’s helideck is Sigorsky S-61N and S-92.
“Energean Force” carries two cranes, with rating capacity 100 mt. and 20 mt. each and can operate at a maximum wave of 8,2 ft. at 11 sec. and at a maximum wave speed of 40 knots.
Fortuna, the jack-up rig from GSP, drilled wells PB-23A and PB-34 in 2013.
PB-23A had a final depth of 2,987 metres, while PB-34 had a final depth of 3,022 metres
Saturn, the jack-up rig from GSP, drilled wells PA-35 and EA-H2 in 2011.
PA-35 well was drilled from Prinos Alpha Platform and went to 2,976 metres. EA-H2 at the Epsilon Oil Field went to 4,808 metres.
The jack-up rig ENSCO 85 drilled wells EA-H1 and PB-14C in 2009 and 2010 respectively.
During the development of Epsilon Field, the Extended Reach Drill (EA-H1) set a record in the Mediterranean, creating the longest well drilled in Greece to date, with a length of 5,297 metres. The PB-14C well at the Prinos Oil Field reached 2970 metres.
The jack-up rig Energy Exerter, from Northern , drilled ERD in Prinos North (PNA-H3) in 2009.
The well was side‐tracked from the old PNA‐H1 well and drilled down to 4388 metres
SINO THARWA ST2
Sino Tharwa ST2 completed two wells in West Kom Ombo in 2011, which reached 990 and 915 metres, respectively.
Two exploration wells have been completed in East Magawish. In 2012, Sengli Bohai drilled the well EM-1 at 4,114 metres and EDC/EDC10 drilled EM-1 ST-1 at 4,130 meters a year later.
Both were ERD and drilled from onshore to offshore in an environmentally sensitive area, close to the tourist resort El Guna.