Earlier this week, Neptune Energy announced the award of a four-wells contract to Borr Drilling. Part of this programme is an exploration well in the northern Dutch offshore, which is known for its shallow gas fields – and prospects.
Shallow gas in the North Sea is mainly found in shallow marine to continental (deltaic) deposits of Plio-Pleistocene age. In seismic data, shallow gas appears as high amplitude seismic anomalies, so-called bright spots. Despite the fact that shallow gas forms a challenge for production because of the unconsolidated and shallow nature of the reservoirs ( <1 km), several fields in the Dutch sector are successfully producing the gas. In the UK, the Aviat field operated by Apache to power the Forties platform is an example of a shallow gas accumulation.
The block Neptune Energy aims to drill in is F05, which straddles the Central Graben in the east and the Step Graben in the west. Based on an inventory of shallow gas pockets as presented by Energie Beheer Nederland (EBN) in 2012, there are four shallow gas leads in the F05 block, none of which are fully enclosed within the boundaries of the block.
Read more about shallow gas in the Dutch sector in this report produced by TNO – Geological Survey of the Netherlands.
Looking at the sizes of the shallow gas prospects in and around the F05 block, it seems likely that Neptune will drill the one in the west that has already been penetrated by well F05-2. Drilled in 1982 by BP, the target of this borehole was probably a Triassic prospect. At the time, shallow gas was mostly seen a drilling risk.
EBN also presented a resource potential estimate for the so-called F04/F05-P1 shallow gas prospect. Based on seismic interpretation and well log analysis, the P50 estimate for the prospect is 2.7 BCM, which equates to almost 17 MMboe. As a comparison, the A12 shallow gas field which is currently being operated by Petrogas had an initial ultimate recoverable of 6 BCM or 38 MMboe.
With infrastructure close by and an urgency to tap into new domestic (offshore) gas resources now that the Groningen field will soon cease production, remaining shallow gas prospects such as F04/F05-P1 certainly seem worth to go after.
HENK KOMBRINK
The outlines of the shallow gas pockets as shown on the map above have been taken from this EBN presentation.
