Shallow-water gas field redevelopment
South Akcakoca Sub-Basin (SASB) gas field is one of the biggest natural gas production and development projects located in the Black Sea, offshore Turkey, at a water depth of less than 100m.
Trillion Energy, a company based in Canada, came to own an interest in the project through the acquisition of Park Place Energy Turkey (PPETL), which owned 36.75% interest in the SASB, in 2017. Trillion Energy acquired a further 12.25% working interest in the project in January 2018 to increase its total working interest to 49%. Türkiye Petrolleri Anonim Ortaklığı (TPAO) owns the remaining 51% stake in the field.
PPETL commenced production from phases one and two of the SASB between 2007 and 2011, while Trillion Energy plans to develop the third and fourth phases from 2020 to 2022.
Development of the first two phases of the SASB gas project involved an investment of $608m.
The SASB gas field encompasses a total license area of 12,385ha, fully covered by a 3D seismic survey. Natural gas in the field is found in the sandstone reservoirs of the Eocene era, lying at a depth between 1,100m and 1,800m below the seabed.
It has so far produced 41.66 billion cubic feet (bcf) of gas. The field achieved peak gas production of 6.5 billion cubic feet (bcf) a year in 2011. The wells currently produce 40 million cubic feet (mcf) of gas a year.
Phases one and two had an 82% success rate in the drilling of wells and finding gas.
Operations have been performed to increase the lifespan of the wells under phases and two, including a reduction in producing pressure to improve gas production, leading to a 50% increase in production to 1,517mcf/d.
The SASB gas field infrastructure includes 23 wells and four offshore unmanned wellhead platforms namely Ayazli at 78.5m of water depth, Dogu Ayazli at 70.5m of water depth, Akkaya at 61m, Akcakoca at 94.5m, associated pipelines, and Cayagzi onshore gas processing plant.
The redevelopment of SASB encompasses the development of the field based on the economic viability of the four gas fields in the sub-basin. GLJ Petroleum Consultants is developing a report on the prospective resources, which is expected to be released in July 2020.
Trillion Energy will execute rig-based operations on the existing wells tied-back to the pipeline to enhance the production of the wells. Additionally, four previously drilled, undeveloped, proven discoveries are planned to be re-drilled from the existing platforms and tied-back to the existing pipeline infrastructure.
It estimates to produce approximately 10.8bcf of gas from the four undeveloped discoveries. The company’s share of expenditure for the development is estimated to be $26m.
The third and fourth phases of development will involve up to 17 new wells as well as various re-entries.
The initial phase of development included the drilling of 17 wells to a total depth of 1,500m below the seabed to undertake partial development of the Ayazli, Akkaya, and Dogu Ayazli gas fields.
The Akcakoca field, discovered in 2006, was developed through the drilling of six wells in phase two of the project and commenced production in 2011.
All the platforms are connected to the shared processing facilities at Cayagzi gas plant via a 25km-long and 12in diameter pipeline. The plant can process up to 75mcf of gas a day.
The processed gas is transported via an 18.6km-long and 16in diameter onshore pipeline, which is tied-back to the national gas transmission network operated by state-owned BOTAS Petroleum Pipeline Corporation.
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