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Nitrogen contents in the northwest Netherlands offshore area

Relatively high nitrogen contents are found in Carboniferous rocks in the southern part of the D&E-blocks in the Netherlands offshore area. Unfortunately, data are lacking for the northern D&E-blocks, which are open for exploration. This report aims to explain the observed nitrogen contents in the southern part of the D&E-blocks, which might help predict nitrogen contents further north. A few factors possibly cause enhanced nitrogen contents in the study area. First, due to a low maturity in the northern part of the E-blocks, the succession might still be (partly) in the “early nitrogen” phase of generation (prior to the main gas generation phase). Secondly, limited availability of high-quality source rocks in the northern part of the E-blocks might have led to a relative enrichment in nitrogen. The influence of volcanic rocks is another factor that has to be taken into account. Local heating might have caused local enhanced generation of nitrogen, possibly from shales. Although these factors might have resulted in higher nitrogen contents, migration of gas (generated in the Step or Central Graben or Cleaverbank High) to the adjacent northern E-blocks is a process which can well be active today. Unfortunately, the nitrogen content of this gas from the Step Graben is unknown. Although these factors pose uncertainties to
the expected nitrogen content in the northern D&E-blocks, the area can still be
regarded as prospective.