During 2012 FOGL drilled two wells in the deep-water area of its licences using the Leiv Eiriksson rig. The rig arrived in the Falkland Islands in early 2012 where it drilled two wells for Borders and Southern Petroleum Plc. (B&S), before commencing the FOGL drilling programme. The first well in the FOGL programme was on the giant Loligo prospect and the second on the Scotia prospect.
The Loligo well (42/07-01) demonstrated a working hydrocarbon system in the northern part of the East Falkland basin and that Loligo is a viable stratigraphic trap. The main hydrocarbon phase encountered within all the reservoir objectives was gas.
The well was drilled to a total depth of 4,043 metres and penetrated 6 Tertiary aged reservoir objectives: T1, T1 deep, T2 (Trigg), T2 deep (Trigg deep), T3 (Three Bears) and T5. These reservoirs had all been identified on the basis of their seismic amplitude responses. Analysis of wireline log data indicated that all six targets comprised gas charged fine grained sandstones and siltstones. FOGL interprets that these sediments have been deposited either outside, or at the distal (outer) end of the slope channel system.
Gas bearing zones were encountered over a 1,300 metre vertical interval from 2,420 to 3,720 metres. Petrophysical analysis of the T1 to T3 intervals inclusive (2,420 to 2,885 metres) indicated porosities ranging from 18% to 35% in the gas bearing zones. Due to the thin bedded nature of these sediments it was difficult to assess precisely both hydrocarbon saturation and the total net hydrocarbon bearing reservoir. Preliminary estimates however, suggest hydrocarbon saturations ranging from 40% to 60% and net hydrocarbon bearing reservoir of between 10 and 20 metres.
Within the T5 target two main hydrocarbon bearing zones were encountered (3,462 to 3,558 metres and 3,608 to 3,705 metres). The net hydrocarbon bearing reservoir in these two zones was 46 and 59 metres respectively. Porosities ranged between 23% and 30%, averaging 24% and hydrocarbon saturations between 40% and 75%.
Attempts were made to obtain pressure data and collect fluid samples. These were unsuccessful, probably due to the fine grained nature of sediments in the gas bearing zone and also, not having access to the specialised test equipment appropriate for this type of formation.
Further detailed evaluation of all the well data, together with the existing seismic is now ongoing in order to better define reservoir distribution and more precisely map the channel systems. These studies will facilitate a better assessment of resource potential and also help define the work that will be required to further appraise this discovery over what is a large complex.
Preliminary estimates indicate that the Loligo complex could contain gas in place (GIIP) between 50 and 100 trillion cubic feet (TCF).
Well 31/12-01 was drilled to a depth of 5,555m. The well penetrated the mid Cretaceous aged reservoir objective on prognosis. The Scotia objective had been identified on the basis of its seismic amplitude response. Strong gas shows (C1 to C51) were encountered whilst drilling the target section. Interpretation of wireline log data indicated that the target interval 4719m to 4769m comprised 50m of hydrocarbon bearing fine grained sandstones and claystones. The wireline logs also indicated that, at this location within Scotia, the sandstones form fairly poor quality reservoir, although some zones have up to 20% porosity. Other thin hydrocarbon bearing sandstones were encountered beneath the main target in the interval 4900m to 5164m. Subsequent evaluation of the main interval using a wireline formation testing tool did not flow hydrocarbons, indicating that the reservoir has low permeability.
The well was deepened below the main target in order to penetrate and sample Cretaceous aged source rocks. Rock cuttings and sidewall core samples have been obtained from several potential source rock intervals and are undergoing detailed geochemical analysis. The results should provide vital information on the quality and maturity of these source rocks and also provide a better understanding of the distribution of oil and gas within this part of the South and East Falklands basin.
The Scotia well has proven a working hydrocarbon system in the mid Cretaceous Fan play and has also demonstrated that Scotia is a viable stratigraphic trap.
View the 2012 Drilling Programme (PDF) presentation.