Investigations of sand resources for the Danish North Sea energy island. Aggregate mapping for the Danish Energy Agency

Pursuant to §2 of Act No. 2379 of 14 December 2021 on the planning and construction of an energy island in the Danish North Sea, the Danish Minister for Climate, Energy and Supply mandated the Geological Survey of Denmark and Greenland (GEUS) to initiate the relevant exploration of sand resources. The execution of the task is coordinated with the Danish Energy Agency (DEA), and survey activities and reporting regarding raw material mapping follow statutory requirements from the Danish Environmental Protection Agency (DEPA).

Following a desk-top study focused on pre-selecting potential areas of sand resources within a limited distance from the planned energy island, three subareas were selected for detailed geophysical studies and sediment coring by GEUS in 2022.

A first vibrocoring campaign in late May 2022 verified the existence of larger potential sand resources in two of the screening areas, Area A and Area B. The areas contain large marine sand bank structures situated immediately to the north-west and to the west of the planned energy island site. In a third Area C, the vibrocores carried out showed relatively thin marine sand deposits on top of late glacial clay-fine sand deposits, not suitable as sand resources. Consequently, a following detailed seismic survey and follow-up vibrocoring campaign in June-August 2022 focused on selected parts of Area A and B only.

For Area A, detailed sand resource mapping confirmed the existence of a large marine sand bank structure with a maximum thickness of up to c. 12 m. In marginal parts of the survey area, sand bank thickness thins to almost zero. The sand bank structure overlies fine-grained late glacial to glacial deposits, with no resource potential. 30 vibrocores with grain size analyses from Area A pinpoint that suitable grain sizes (medium-coarse sand) are found only in the upper 3-5 m of the sand bank unit. Moreover, the thin sand cover of the sand bank margin appears to be dominated by fine-grained sand. A conservative estimate of net sand resource volume in Area A, represented by the upper 3 m of the delimited resource area, gives a total volume of c. 172 million m³ sand suitable for energy island construction.

For Area B, resource mapping confirmed the existence of a marine sand bank structure with a maximum thickness of up to c. 14 m. In the northern tip of the area, sand bank thickness thins to almost zero. In the southern part, two marine sand units have been identified. The older unit, having a variable internal structure, appears in general to be too fine-grained. The younger unit consists of medium-grained sand forming large clinoform foresets building out towards the north. 13 vibrocores with grain size analyses verify that the upper c. 3 m of the younger sand bank unit constitutes the potential resource in Area B. A conservative estimate of net sand resource volume in Area B, represented by the upper 3 m of the delimited resource area, gives a total volume of c. 80 million m³ sand suitable for energy island construction.

GEUS’ investigations have been able to confirm that suitable sand resources are found close to the planned North Sea Energy Island site. Based on a simple distance relationship, resource Area A is considered to be a potential primary sand extraction area, and resource Area B is a good alternative area. Due to poor resource quality, Area C disqualify as a potential resource area.