FEModelling of the North German Basin - Considerations on Choosing Boundary Conditions

Abstract. Brine migration into potential drinking water aquifers due to the injection of CO2 into deep saline aquifers is one of the potential hazards associated with the Carbon Capture and Storage technology (CCS). Thus, in any site selection process, an important criterion should be the evaluation of brine migration resulting from the injection. We follow an interdisciplinary approach using participatory modeling to incorporate stakeholder opinion at an early stage in order to discuss and evaluate model conception and relevant scenarios for brine migration. The basis for this approach is a realistic (but not real) on-shore site in the North German Basin with characteristic geological features for that region. Our model fully couples flow in shallow and in deep saline aquifers including variable-density transport of salt and a realistic description of the top surface boundary conditions with groundwater recharge and rivers. We investigate different scenarios to identify relevant system components. Further, different model simplifications are compared and discussed with respect to the relevant physical processes and the expected data availability, i.e. to find a model as complex as necessary and as simple as possible. It becomes clear that the initial salt distribution plays a key role as to where noticeable concentration changes may occur. Also the boundary conditions are important for determining the amount of vertically displaced brine. Simplifications in the model setup, such as neglecting variable-density flow or simplifying the complex geometry may prove valid options given sparse data availability.

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Seismic tomographic interpretation of Paleozoic sedimentary sequences in the southeastern North Sea

Geophysics ◽

10.1190/1.1996908 ◽

2005 ◽

Vol 70 (4) ◽

pp. R45-R56 ◽

Cited By ~ 10

Author(s):

Lars Nielsen ◽

Hans Thybo ◽

Martin Glendrup

Keyword(s):

North Sea ◽

Velocity Structure ◽

Seismic Velocity ◽

P Wave ◽

Wide Angle ◽

North German Basin ◽

Sedimentary Sequences ◽

The North ◽

Crystalline Crust ◽

German Basin

Seismic wide-angle data were recorded to more than 300-km offset from powerful airgun sources during the MONA LISA experiments in 1993 and 1995 to determine the seismic-velocity structure of the crust and uppermost mantle along three lines in the southeastern North Sea with a total length of 850 km. We use the first arrivals observed out to an offset of 90 km to obtain high-resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust. Seismic tomographic traveltime inversion reveals 2–8-km-thick Paleozoic sedimentary sequences with P-wave velocities of 4.5–5.2 km/s. These sedimentary rocks are situated below a Mesozoic-Cenozoic sequence with variable thickness: ∼2–3 km on the basement highs, ∼2–4 km in the Horn Graben and the North German Basin, and ∼6–7 km in the Central Graben. The thicknesses of the Paleozoic sedimentary sequences are ∼3–5 km in the Central Graben, more than 4 km in the Horn Graben, up to ∼4 km on the basement highs, and up to 8 km in the North German Basin. The Paleozoic strata are clearly separated from the shallower and younger sequences with velocities of ∼1.8–3.8 km/s and the deeper crystalline crust with velocities of more than 5.8–6.0 km/s in the tomographic P-wave velocity model. Resolution tests show that the existence of the Paleozoic sediments is well constrained by the data. Hence, our wide-angle seismic models document the presence of Paleozoic sediments throughout the southeastern North Sea, both in the graben structures and in deep basins on the basement highs.

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