Evaluation and risking of the seal capacity for CO2 storage in the Nini West Oil Field, Denmark. Project Greensand WP 4 TRL3

Research output: Book/ReportReport (publicly available)

Abstract

The Nini West Oil Field is located in the Siri Canyon within the Danish North Sea. The canyon lies east of the Central Graben and extend from here and across the Ringkøbing-Fyn Basement High. The Siri Canyon formed in the Paleocene and feed a turbidity system that transported materiel from the Norwegian Stavanger Platform whereon glauconitic sand formed and to the Danish Central Graben. The turbidite system backstepped through the Palaeogene and deposited a series of isolated sand bodies imbedded in deep-water pelagic claystone within the Palaeocene-Eocene Rogaland Group (Våle to Balder Formation). The oldest of the sands are sealed by units within the Rogaland Group and the youngest sands are sealed by the above lying Eocene Horda and the Oligocene to Miocene Lark Formation that combined typically is one kilometre thick.

The Siri Canyon is characterised by overall low natural seismicity. The latest tectonic event that affected the North Sea area was the opening of the North Atlantic and as consequence ridge push forcers still affects Northern Europe. The primary seal to the Nini West Field is in the Nini-4 well 340 m thick and composed of shales that belong to the Eocene to Miocene Horda Formation and the lower to mid Lark Formation. The Horda Formation is characterised by greenish grey to greyish green fissile mudstone. Subordinate limestone benches and thin layers of black mudstones occur at some levels in the formation. The lower Lark Formation is dominated by dark, greenish grey, non-fissile mudstones with subordinate intervals of brownish grey mudstones. The secondary seal is in the Nini-4 well 550 m thick and belong to the mid to upper Lark Formation. This shale is composed by pale to dark brownish grey mudstones with subordinate intervals of greenish grey mudstones. The combined seal sequence is thus almost 900 m thick in the Nini West area. The above lying strata i.e. the remaining c. 800 m belongs to the Nolde Sand and the Nordland Group and is considered overburden.

During formation of the primary and secondary seal, smectite was the dominate clay mineral and due to the common mineralogical make-up of the shales the basic rock properties are very alike between the different shale formations as seen from analysis of the plasticity of the shales and the rock strength tests. Most of the variation appear to be related to the presence or absence of organic matter and/or radiolaria rich material that may or may not be present in all formations.

Measured shale porosities range between 15–25.8% for the lower Hordaland Group and measured transient brine permeability of the Sele Formation range between 1 and 20 nD pending on being orientation.

Rock mechanical tests have been performed on all shale formations expect the Lark Formation from where no core data within the Siri Canyon exist. The bulk of the tests were made on core material from the Sele and Lista Formations but also tests from the Horda Formation have been made. Unconfined compression strength (UCS) (measured and estimated) range between 8.1–13.3 MPa with the lowest value measured in the Sele Formation and the highest value measured in the Lista Formation and with the Horda Formation as having an intermediate measured value (10.1 MPa).

We present a risk analysis for the seal capacity for the Nini West field seal complex following the risk factors presented by Bruno et al. (2014). The risk factors include 18 different parameters of which the current state of knowledge allows 12 to be evaluated here either with a reasonable certainty or provisionally pending on more data and analysis. The evaluation show that none of the evaluated parameters falls within the high risk category of Bruno et al. (2014) and that most of the evaluated risk factors fall within the low to medium risk group. Most of the risk parameters that has been assigned a medium risk need, however, additional analysis and characterisation before final evaluation can be made. Compared to other seal complexes evaluated according to the Bruno et al. (2014) risk scheme, then the caprock capacity of the Nini West Field currently have a relative low risk score although not all risk factors have currently been evaluated.
Original languageEnglish
Place of PublicationCopenhagen
PublisherGEUS
Number of pages58
DOIs
Publication statusPublished - 23 Sept 2021

Publication series

SeriesDanmarks og Grønlands Geologiske Undersøgelse Rapport
Number26
Volume2020

Keywords

  • Denmark

Programme Area

  • Programme Area 3: Energy Resources

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