Offshore staff
OSLO, Norway — The Norwegian Petroleum Directorate (NPD) is urging E&P companies to find ways of harnessing gas in tight reservoirs across the Norwegian Continental Shelf.
These are low-permeability reservoirs that typically cannot be produced using conventional wells and require measures to improve gas flow. Fracturing and multi-branch wells are currently the most favored methods for recovering these resources.
Another approach is to drill multiple slim boreholes in the same well to increase reservoir exposure and make it easier for hydrocarbons to flow.
To date, the NPD notes, these techniques have been applied in Norway mainly to improve oil recovery whereas in the Gulf of Mexico and on the UK shelf, applications have been more gas-oriented.
Production from tight reservoirs is often only viable if the development can be tied back to existing infrastructure, because of the relatively low production rates over a long period.
According to Arne Jacobsen, assistant director of technology, analyses and coexistence, "It's often expensive to implement technology, and profitability can be marginal. We encourage the companies to think outside the box and work across fields – and thereby achieve potential economies of scale."
He sees potential for cost savings through companies co-operating to co-hire vessels and drill multiple wells in an area.
The NPD’s estimate for resources in tight reservoirs on the Norwegian continental shelf in its reports from 2017 and 2019 showed strong potential across each sector.
Mapped volumes in place in tight reservoirs in the southern Norwegian North Sea are around 750 MMcm of oil and 90 Bcm of gas, much of it in chalk reservoirs in the Ekofisk, Eldfisk and Valhall areas. In the northern part of the North Sea, mapped oil volumes in tight reservoirs are 360 MMcm with 80 Bcm of gas, within sandstone reservoirs but also in the overlying Shetland chalk at Gullfaks, where Equinor is applying water injection and horizontal wells to improve oil recovery.
In the Norwegian Sea mapped tight volumes are 130 MMcm of oil and 420 Bcm of gas, all in sandstone reservoirs. Examples are the Lavrans, Linnorm, Noatun and Njord Nordflanken 2 and 3 discoveries, all with tight reservoir zones. The licensees are assessing use of various techniques to improve profitability.
Slim-hole technology has been adopted in tight zones in the Garn formation on Smørbukk Sør. However, other fields with large tight reservoir volumes in place have defeated attempts at profitable development solutions. One example is 6506/6-1 Victoria in the Norwegian Sea, which has been relinquished.
In the Barents Sea, the resource base is less clear: known tight reservoirs are in sandstone in the Triassic interval.
12.07.2023
