Fluid inclusions and PVTX modelling: examples from the Garn Formation in well 6507/2-2, Haltenbanken, Mid-Norway S. Teinturier a, * , J. Pironon a , F. Walgenwitz b a CREGU-UMR G2R-7566, BP23, F-54506 Vandoeuvre-le `s-Nancy, France b CSTJF, TotalFinaElf, Avenue Larribau, F-64018 Pau, France Received 27 September 2001; received in revised form 12 June 2002; accepted 24 June 2002 Abstract 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 8C and 50 bar; the second to the petroleum fluid arrival in the biphase field of a critical system around 100 – 120 8C 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 8C and 230–280 bar) within the last few million years of a short and relatively rapid burial. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Fluid inclusion; PVT modelling; Haltenbanken; Hydrocarbon; Petroleum; Quartz cementation 1. Introduction Fluid inclusion studies are a powerful tool in under- standing and deciphering the diagenetic history of petroleum reservoirs. Microthermometry, confocal scan- ning laser microscopy (CSLM), Raman and FT-IR spectro- scopies coupled with thermodynamic modelling, allow the reconstruction of accurate PVT conditions of aqueous and petroleum fluid entrapment occurring in sedimentary basins (Aplin et al., 1999; Pironon, Canals, Dubessy, Walgenwitz, & Laplace-Builhe, 1998; Pironon, Thie ´ry, Ayt Ougougdal, Teinturier, Beaudoin, & Walgenwitz, 2001). Nevertheless, this approach must take into account the relationships between quartz cementation and oil migration to clearly define diagenesis events and chronology. The presence of petroleum inclusions within quartz cement is not conclusive evidence that these inclusions represent the initial petroleum fluid composition and that they were simultaneously formed at the same time that quartz cementation. The ability of petroleum emplacement to inhibit quartz cementation has been debated by many authors and depends mostly on the controls on silica transport from its source to precipitation (Worden & Morad, 2000). Oil inclusions inside quartz cements, similar homogenisation temperature ranges and/or relative similar volumes of cement or porosities between water and oil-saturated zones are the prime empirical arguments of authors who consider that oil emplacement does not halt quartz cementation (Ramm, 1992; Saigal, Bjorlykke, & Larter, 1992; Walderhaug, 1990). The concept that quartz cementation is inhibited by oil saturation is based on significant differences of porosity in some oil-bearing sandstones reservoirs (Gluyas, Robinson, Emery, Grant, & Oxtoby, 1993). The purposes of this paper are (1) to describe unusual microthermometric behaviour and new analytical data derived from fluid inclusion studies and quantitative spectroscopic analyses (2) to propose a PVTX model for aqueous and petroleum fluid entrapment and (3) to discuss the relationships between quartz cementation, petroleum migration and emplacement in the Garn Formation in well 6507/2-2, in the Haltenbanken Mid-Norway area. Previous fluid inclusion studies in the Haltenbanken 0264-8172/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0264-8172(02)00055-7 Marine and Petroleum Geology 19 (2002) 755–765 www.elsevier.com/locate/marpetgeo * Corresponding author. Tel.: þ 33-3-83-91-38-12; fax: þ33-3-83-91-38- 01. E-mail address: stephane.teinturier@g2r.uhp-nancy.fr (S. Teinturier).