... the Obelix discovery is finally appraised. Read the abstract from the last Hydrocarbon Habitats seminar in Oslo and Stavanger.
The Obelix = Neiden are both informal names of the middle high of the crestal area of the Loppa High. The warm-water carbonate reservoirs of the Gipsdalen Group were deposited on an eastward tilted distally steepened ramp with polygonal network build-ups during the Moscovian to Gzelian. The Loppa High was uplifted, rotated towards east, subaerially exposed and karstified during the mid-Permian to Anisian. Along the crestal parts of the Loppa High, the deep erosion resulted in direct contact between the basement and the overlying Triassic succession that transgressed the “Loppa High Island”. Thus the Ladinian mudrocks represent the top seal of the structure, while the basement rocks may be the base seal.
Well 7220/6-1 was drilled in 2005. It aimed to test predominately parallel seismic facies (interpreted as non-reservoir mud-dominated carbonates) in an otherwise chaotic dominated seismic facies area interpreted as karstified carbonates. Karstified carbonates were regarded as a high-risk for drilling hazards and should therefore be avoided in the well. The well penetrated 108m of Nordland Group, 662m of open marine and paralic deposits of the Snadd Formation, 86m of karst breccias of mid-Permian and Early Triassic age (erroneously called Ørn Formation in the completion log), 212m of lagoonal dolomudstones and dolowackestones of the Ørn Formation, 47m of alluvial fans and marine carbonates of the Falk Formation and finally 57m of fractured quatrzitic metasandstones the TD at 1540mRKB.
The well proved good oil shows from 1138mRKB and 1430mRKB, corresponding to the spill point of the structure towards north. The STOOIP volume of the structure, including up dip volumes to the top of the structure at ca. 970mRKB, was estimated to be 450×10⁶Sm³, based on the well results. The up dip potential of the structure was estimated, prior to drilling, to be 30×10⁶Sm³. The average porosity of the dolomitized reservoir was 12% and with average permeability below 1mD. The oil-wet carbonate reservoir had oil saturation varying between 20 and 40%, with maximum oil saturation of 60% in a thin zone. The low oil saturation was interpreted as caused by leakage of the structure. Pressure points proved a water gradient. Non-reported pressure points have an oil gradient that also included the two outliers amongst the reported pressure points. Four MDT water samples (1151,5, 1184,5, 1338 and 1377,1 mRKB) were taken. Ca 10ml of oil was reported from the 1184,5m sample. According to the completion report from the well the oil had a measurable gravity of 29 deg. API after three weeks of exposure to atmospheric conditions, and was found to be mildly biodegraded.
C&C carbonate data base from global carbonate fields included data from Gipsdalen Group analogues in Siberia, Arctic Russia. One big field have an average oil saturation of 70% in oil wet dolomitized algal build-ups reservoirs and with oil pressure gradient. In the adjacent lagoonal mud-dominated dolomites non-reservoirs the oil saturation varied between 20 and 40% associated with a water pressure gradient, as in well 7220/6-1!
Well 7220/6-2 is presently drilled by Lundin and partners just north of the 7220/6-1 well. The new well may wake up a mistreated elephant on the Loppa High, Barents Sea.
Neiden – the Obelix discovery finally appraised
Elvebakk Moski, G.* Hogstad, K.**, Skeie, J.E.*** & Svånå, T.A.****, 2016
Nord Universitet, **Pensjonist, ***Aker BP, ****Affraz Advisers/Aurelia Geo AS.