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Microbially Mediated Magnesite Precipitation Destroying Reservoir Quality in the Volpriehausen Sandstone, Denmark
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 80th EAGE Conference and Exhibition 2018, Jun 2018, Volume 2018, p.1 - 5
Abstract
Cutting material from well Olga-1X, Denmark, was studied to understand the contradicting reservoir properties of the Lower Volpriehausen Sandstone Member. Although petrophysical assessments concluded the reservoir quality to be good with around 13% porosity, permeability was interpreted from well tests to be very low. Magnesite, a rare mineral in ancient geological settings, was discovered in the Lower Volpriehausen Sandstone Member of Olga-1X. Magnesite is seen forming a cement between quartz grains, blocking pore throats. Particulate organic matter is often associated with the magnesite. This context, a micritic nature of the carbonate and wavy sediment lamination support the interpretation of magnesite formation in microbial mats. The magnesite has likely been precipitated in a shallow, relatively saline lacustrine lake positioned below the average water table, while in emerged phases incipient desert soils could form. It is expected that water drained off the Paleozoic Rynk0bing-Fyn High 30 km east via flashfloods. The water likely had a high Mg component due to Mg-Ca pyroxenite in the source area and has the appropriate geochemistry for magnesite to form. This study highlights the potential value that can be achieved from combining analysis of drill cuttings with seismic and wireline data to define new sedimentological models.