Palaeo-migration

Fluid communication across faults and within faults may thus be genetically linked to both petroleum migration and overpressure development (cf. Figs 8 10). In particular, palaeo-migration of petroleum from the Are source... 

Why did these drained structures not refill later with hydrocarbons after leakage It follows logically that structures which earlier received hydrocarbons, like the 6505/11-1, 6506/12-4 and 6406/3-1 structures, have communicated with a generative source rock basin where the Spekk Formation was mature. Hence, palaeo-migration conduits towards the traps existed for these structures. Is this migration avenue still active or was it shut off, e.g. by structural movement or sealing faults Or could it be that... 

Eggins, S., De Deckker, P. Marshall, J. 2003. Mg/Ca variation in planktonic foraminifera tests implications for reconstructing palaeo-seawater temperature and habitat migration. Earth and Planetary Science Letters, 212, 291-306. 

It is, in our opinion, based on the geochemistry of the undersaturated oil in the Cretaceous Lange Formation strata above Smorbukk, a likely assumption that parts of the leaked oil from a palaeo-accumulation in Garn in Smorbukk migrated vertically by fracture-induced mechanisms into the Cretaceous strata above (cf. Fig. 7). 

This serves to illustrate the importance of detailed core analysis and geochemistry to decipher the status of drilled structures, i.e. other data points than well tests and modelling are needed to construct a model for palaeo-and recent petroleum migration in a basin. The fact that the structures earlier contained a fluid phase (not, as assumed, only gas) places a totally different perspective on the timing of oil migration relative to caprock formation, structural development, and field filling in Halten Vest. 

Radiogenic helium, radon and radium, each with a different mechanism of migration, should be effective even in completely reduced systems. Examples of these occurrences are tabular Colorado Plateau type deposits related to reducing conditions in a palaeo-river bed and rereduced host rocks where roll fronts are no longer in proximity to surface oxidation. 

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