AthenaThelikely development of the Athena oil pool consists of five producingwells and one water injector tied back to an FPSO via subsea manifoldat the current drill centre location. The FPSO will be tankeroffloaded and provide all services and controls for the field. Thegross anticipated initial rate from the field will be approximately22,000 barrels of oil per day under the current development scenario.
Thepreviously defined development scheme was re-examined in the light ofrising oil prices during 2009. This work concluded with the decision topush forward with developments. Prior to the launch of the AthenaProject in February 2010 extensive engineering studies were undertakento progress the FPSO layout design plans and capture failing costs fordevelopments. Revisions to the existing Environmental Assessment andField Development Plans have been made with resubmission occurring H12010 with acceptance possible in early H2 2010. It is likely thatdrilling and installation work will take place and be completed early2011 to allow first oil in mid 2011 with follow on drilling potentialto occur into 2012.
Subsurface
Athenahas potential for increased reserves. The envelope of the reservoirsand could be much greater than that to which reserves have beenascribed and, as a stratigraphic pool, only future drilling willdisclose the effective extent of the porous reservoir.
The Athena field is located on a structural highpoint between the Jura and West Scapa Basins, which developed duringMesozoic rifting. The Leek and Scapa sandstones of the lower ValhallFormation were sourced from the Halibut Shelf to the south of theAthena field. Turbidite sands entered the basin at the junction througha transfer or fault zone between the NW/SE trending Jura Basin marginof the Halibut Shelf, and the SW/NE trending margin towards the WestScapa Basin. An area of low structural relief on the underlying BCUsurface can be seen on the seismic interpretation. The sands werelocally sourced from reworked Devonian alluvial clastic sediments thatform the basement of the Halibut Shelf, possibly being eroded byfluvial systems on the exposed Halibut Horst, and stored in a shallowshelf environment. Turbidite sand lobes were deposited into the basinenvironment, initially directed to accommodation space created in theJura Basin, but eventually filling to the east and onlapping onto thebasin margin towards the north. The Leek and Scapa Sandstones pinch outinto the calcareous Valhall Marls, forming the stratigraphic trap forthe Athena Field to the north. To the south, the Leek and ScapaSandstones either onlap or are truncated against fault scarpconglomerates derived from the Halibut Shelf edge.
Deposition of conglomerate / breccia facies alongthe edge of the Halibut Shelf is recognised in the area, with severalexploration wells encountering tight conglomerates (e.g 14/18a-8, 8z)between Athena and the Scapa Field to the east. No conglomerates havebeen encountered in the main Athena field area, but are interpreted tohave been encountered in well 14/18b-17z. The location and nature ofthe boundary between the fault scarp conglomerates encountered in14/18b-17z and the Leek Sandstone of the main field area is currentlynot known.
The level of cementation appears to increase towardsthe north of the field, and towards the edges of individual sand lobeswhere they become thinner (seen when comparing 14/18b-15a with14/18b-12). This suggests that with increasing distance from theclastic source area, with lower depositional rates, predominantlycarbonate deposition of the Valhall Formation background takes over.
Sproule have estimated the Corporation's net reserves in Athena to be:
| Category |
Oil (MMbbls) |
| Proved |
3.31 |
| Probable |
2.18 |
| Possible |
4.59 |
| TOTAL |
10.08 |