Fluid inclusions and PVTX modelling: examples from the Garn Formation in well 6507/2-2, Haltenbanken, Mid-Norway

Fluid inclusions study and multi-techniques quantitative analyses have been coupled to reconstitute PVTX conditions of aqueous and petroleum fluid entrapment of a local Haltenbanken area (well 6507/2-2) from the Garn Formation. Unusual low temperature behaviour showing the liquid portion separating into two liquids has been described. This behaviour is typical of a gas condensate/volatile mixture with high methane content and heavy alkanes. The variable liquid-vapour ratio, compositions and morphologies of all petroleum inclusions can be interpreted as a result of a combination of heterogeneous trapping and necking down. Thus, all petroleum inclusions can be related to a single petroleum source. Three main episodes of fluid entrapment can be distinguished. The first one corresponds to the water trapped within detrital quartz microfractures, at around 50 degreesC and 50 bar; the second to the petroleum fluid arrival in the biphase field of a critical system around 100-120 degreesC and 190-230 bar. The third one to the main trapping of present-day petroleum inclusions during the recrystallisation of quartz cements (around 110-160 degreesC and 230-280 bar) within the last few million years of a short and relatively rapid burial. (C) 2002 Elsevier Science Ltd. All rights reserved.