The Prinos Field is formed by a low relief faulted anticline, with oil trapped in the Prinos Group reservoir of Miocene Age at a depth of between 2,490 and 2,770 metres TVDSS. The reservoir produces under-saturated sour crude oil with an API gravity of between 27 and 30 degrees.
Prinos contains up to 60 per cent hydrogen sulphide gas. The onshore Sigma plant features facilities to convert it to sulphur. The sulphur is then sold to a local fertilizer plant.
Following exploration of the Prinos Basin in the 1970s, the Prinos Field was discovered in 1974 through the drilling of Prinos-1, the first exploration well drilled in the area. It was developed during the late 1970s and brought into production in 1981.
The initial development of the field took place from 1979 until 1981, following the drilling of the delineation wells which confirmed the extent of the Prinos reservoir,. Facilities were installed offshore and onshore to allow 30,000 bopd to be produced along with associated gas. Two drilling jackets were installed above the Prinos Field and bridge linked to an unmanned offshore processing platform. Via a pipeline, these offshore facilities were linked by pipeline to the shore, where a complex gas and oil processing plant was constructed along with oil storage tanks (500,000 bbl capacity) and offshore loading terminal.
Crude oil production commenced in early 1981, at initial rates of 8,000 to 10,000 bopd, with production peaking at more than 27,000 bopd in 1985. Prinos 2P reserves were initially estimated at 60 million oil bbls, but the field has already produced more than 110 million bbls since 1981.