| Autor: |
Gunn M. G. Teige, H.M. Nordgård Bolås, Lars Wensaas, Christian Hermanrud |
| Rok vydání: |
1999 |
| Předmět: |
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| Zdroj: |
Marine and Petroleum Geology. 16:321-335 |
| ISSN: |
0264-8172 |
| DOI: |
10.1016/s0264-8172(98)00035-x |
| Popis: |
Disequilibrium compaction (undercompaction) is probably the most accepted mechanism for explaining overpressured formations. This mechanism relies on the hypothesis that overpressured shales have higher porosity than normally pressured shales for a given depth. Converted to porosity units, log response data from two Jurassic shales at Haltenbanken and nine Cretaceous and Tertiary shales in the Norwegian sector of the North Sea have been investigated to see whether such a relationship exists in these areas. The depth of the studied shale formations varies between 0.5-5 km. The degree of overpressuring within one formation typically varies by 20 MPa. The log response data show that neither the porosity of massive North Sea shales (derived from sonic and density logs) nor the porosity of Haltenbanken intra-reservoir shales (derived from density and neutron logs) differ significantly between the overpressured and normally pressured stratigraphic units. Distinct differences between the pressure regimes are, however, apparent in the resistivity and sonic log data from deeply buried shales at Haltenbanken. These differences do not reflect porosity variations and are interpreted to reflect textural changes resulting from the overpressuring. These observations demonstrate that the Haltenbanken and North Sea shales do not conform to an undercompaction mechanism for overpressuring, as the overpressured wells fail to show elevated porosity. On the contrary, each formation seems to have been individually compacted according to burial depth, independent of pressure regimes. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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Full Text from ScienceDirect