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New hydrocarbon prospects in the Chalk

The Netherlands represents a mature area for hydrocarbon exploration, and only less obvious targets are left for finding more oil and gas. One of these is the Chalk Group. A multidisciplinary joint industry research project has been proposed to support the E&P industry to target the Chalk, particularly in the Netherlands, by developing and applying new stratigraphic trap and migration/charge models.

The Chalk Group includes important hydrocarbon reservoirs in the UK, Norwegian and Danish sectors of the North Sea. The reservoir-quality Chalk is generally characterised by high porosity and low permeability. Tilted hydrocarbon-water contacts in this Chalk and regional overpressure gradients indicate dynamic basin-wide conditions. While most of the Chalk fields produce from the uppermost part of the Chalk (Maastrichtian and Danian), the lower part of the Chalk Group, and the Lower Cretaceous shales, are considered to act as a regional seal restricting fluid and gas flow and often preserving high overpressures in underlying units. A recent quantitative assessment of the porosity-permeability characteristics of this non-reservoir part of the Chalk reveals that faulting and fracturing near salt structures may locally influence the pressure and the fluid migration conditions, possibly providing vertical pathways for oil and gas to enter and move through the Chalk.

Challenge

Despite major parts of the Chalk Group probably being non-reservoir quality, the hydrocarbons managed to migrate through the Chalk and charge the reservoirs in the uppermost part of the Chalk in the UK, Norwegian and Danish parts of the Central Graben, with Denmark having successfully drilled several fields since 1966. In the Netherlands, the only producing oil field is the Hanze Field, discovered in 1996 in Block F2. Present-day knowledge about the properties and distributions of potential stratigraphic traps, regional seals and leak points/migration paths in the Chalk Group in the Netherlands is scant. A study to enhance the knowledge and understanding of the Chalk in the Netherlands will build on published information and use recent Dutch studies on the Chalk supplemented by TNO's wealth of data, information and knowledge on the Dutch subsurface. In addition, innovative approaches and state-of-the-art tools will analyse and interpret this information and data.

New models

A comparision of the biostratigraphy and paleoenvironmental characteristics, associated compaction and permeability, and migration and charging conditions between the successfully drilled reservoirs in the Danish sector with Chalk conditions in the Netherlands will enable a new stratigraphic trap model and migration/charge model for the Dutch Chalk to be developed. The project will see two phases: a pilot study based on available data and samples, and the development of an exploration model. Successful reservoir prediction requires detailed chronostratigraphic and biofacial models to support the stratigraphic trap model and enable development of a detailed biostratigraphic frame of this interval for biosteering during drilling operations. The approach and results of the pilot will be extended to other Chalk occurrences in the Netherlands offshore, with an initial regional overview followed by a more detailed study on a promising area selected together with the project partners.

Contact

Dr. Johan ten Veen

  • geology
  • seismic interpretation
  • structural geology
  • geomodels
  • petroleum geology
Email

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