Sand was a problem at Fenja, it seems

Sand was a problem at Fenja, it seems

With an appraisal well on the Bue discovery being finalised, the results provide food for thought.

Neptune Energy Norge AS, operator of production licence 586, is in the process of concluding the drilling of wildcat well 6406/12-G-1 H, which is an extension of an observation well for the 6406/12-3 A (Bue) oil discovery.

The 6406/12-3 A (Bue) oil discovery was proven in 2014 in Upper Jurassic reservoir rocks (the Rogn Formation). Before observation well 6406/12-G-1 H was drilled on the discovery, the resource estimate was between 1 and 4 million standard cubic metres (Sm3) of recoverable oil equivalent.

The well’s primary exploration target was to reduce uncertainty in the resource estimate. The secondary objective was to prove petroleum in Middle Jurassic reservoir rocks (sandstone in the lower part of the Melke Formation).

Well 6406/12-G-1 H did not encounter reservoir rocks in either the primary or secondary exploration target. However, the well did encounter a total oil column of 38 metres just above the secondary exploration target in the lower part of the Intra-Melke Formation, of which about 20 meters were of moderate to very good reservoir quality.

In September, we reported on the Fenja drilling campaign that has now been concluded. Looking at cross-sections from publications in the area (see below), we already concluded that the Jurassic sands are probably of a very limited extent. Well 6406/12-G-1 H has proven this.

E-W cross-section from the Vingleia fault complex in the east to the Klakk fault complex in the west. Note the limited lateral extent of the coarse-grained alluvial fan sediments shed from the east. For location, see map at the top of this article. Figure modified after Elliott et al. (2015).

However, the mention of a 38 m oil column just above the secondary target, displaying very good reservoir properties, is rather cryptic when at the same time it is being claimed that both the primary target (Rogn Fm) and secondary target (Melke Fm) reservoirs were not found. Let’s have a more detailed look at this.

Looking at the now updated schematic we produced for the September article below, the 12-3A well on Bue found a thin oil column in the Rogn Fm, which represents the Bue find. NPD Factpages mentions that the mudstones of the Spekk Fm are present below the Rogn Sst, with an estimated thickness of around 30 m. Beneath the Spekk Fm mudstones an interval of Intra-Melke Sandstones was drilled.

Updated schematic diagram illustrating the oil water and gas water contacts in the Fenja wells drilled so far as well as the distribution of sands in these wells. Whilst the outline of Bue initially extended towards 12-G-1 H, it has now been updates as the 12-G-1 H well did not find the Rogn Fm sandstone. Well locations are estimated based on limited information. Source: NPD Factpages.

Unless the 12-G-1 H well drilled a sandstone that is time equivalent to the lower part of the Spekk Fm in 12-3A, we argue that it is more likely that the well did find the secondary Melke Sst target but in a more distal facies. It may therefore be concluded that this newly proven oil accumulation is within the same reservoir unit as the Pil accumulation.

The preliminary calculation of the 6406/12-3 A (Bue) oil discovery has now been reduced to between 0.2 and 1.6 million Sm3 of recoverable oil equivalent, while the estimate for the new oil discovery is between 0.5 and 3.2 million Sm3 of recoverable oil equivalent.


Full reference cited article:

Elliott, G.M., Jackson, C.A-L., Gawthorpe, R.L., Wilson, P., Sharp, I.R. & Michelsen, L., 2015. Late syn-rift tectono-stratigraphic evolution of Vingleia Fault Complex, Halten Terrace, offshore Mid-Norway; a test of rift-basin tectono-stratigraphic models. Basin Research, DOI: 10.1111/bre.12158.