Thermal modelling of magmatic intrusions in the Gjallar Ridge, Norwegian Sea: implications for vitrinite reflectance and hydrocarbon maturation

Abstract

Extensive magmatic activity took place in the VÖring Basin, o¡shore Norway, related to the Early Cenozoic rifting.The break-up of the North-Atlantic at the Palaeocene^Eocene transition induced strong volcanism.There are numerous magmatic sills below 3 km depth in the area.They are predominantly layer parallel and thin compared with their lateral extent. Igneous intrusions, sills and dykes a¡ected the temperature history, and thus need to be taken into account in petroleum prospect analysis.We have calculated the temperature and maturity e¡ects in the sedimentary layers in the Gjallar area associated with the emplacement of single sill and sill complexes. A 120-m-thick sill produces a theoretical vitrinite re£ectance (%R 0 ) 0.8% higher than normal at a distance of 100 m from the sill.Vitrinite re£ectance changes caused by a swarm of seven sills varying from 8 to 80 m in thickness were calculated. It is shown that the calculated thermal pro¢le can account for the observed shift in vitrinite re£ectance in the well. A two-dimensional section crossing the Gjallar Ridge, consisting of numerous magmatic intrusions, is also modelled.The modelled geological development and temperature history over the pro¢le show that there are signi¢cant maturation e¡ects in the interval under investigation. Based on this work, the sill swarm observed in the area could more than double the fraction of the kerogen that has been transformed to petroleum at the (present) depth of 4 km.

How contact metamorphism can trigger global climate changes: Modeling gas generation around igneous sills in sedimentary basins

“…Modeling provided Data provided Intrusion thickness Normalized aureole Lithology of host-rock Barker and Bone (1995) V b -Da 2.2 m $5% D High grade limestone Barker et al (1998) T-F-L C V 0.06 -40 m 30-150% a D Clay/sediments Bishop and Abbott (1995) T V-TOC-RE-GC 0.3-3.0 m 30-70% a D Shale/silty shale Brown et al (1994) T-Ro V 40-60 m 150% a S Shale/limestone Bostick and Pawlewicz (1984) V 3.6-10.4 m 75-100% a D Shale/limestone Clayton and Bostick (1986) V-RE-GC-Da 1.3 m $50% a D Siltstone Cooper et al (2007) V-TOC-Da 0.15-1.8 m 75-110% a S/D Coal/black shale Delaney (1982) T Drits et al (2007) Mi 0.5-80 m $75% b S Mudstone Dutrow et al (2001) T-F-R TOC-Da 11 m 35-55% b D Carbonate/siltstone Finkelman et al (1998) V-RE-El-Mi 1.5 m $35% a D Coal/coke Fjeldskaar et al (2008) T-Ro V 118.5 m $150% c S Silt/shale/sandstone Galushkin (1997) T-F-L C -L D -Ro V 0.9-118.5 m 55-170% a S/D Black shale/silt George (1992) V-RE-GC-Da 3.5 m $70% a D Silt/oil shale Golab et al (2007) Mi Hanson and Barton (1989) T-L C -L D D Jaeger (1959) T-F-L V 100% c Kjeldstad et al (2003) T-F-P-Ro Litvinovski et al (1990) T-L M -P 500 m >>10% b D Clay/pumice Mastalerz et al (2009) V-Da >1.2 m $50% a D Coal Meyers and Simoneit (1999) TOC-RE-Da 1.5 m $60% b S Coal Othman et al (2001) V-RE-GC 0.40-15.7 m S Mudstone Perregaard and Schiener (1979) V-GC 4.5 m $50% a D Shale Peters et al (1983) V-RE-GC 0.2-15 m 50-70% a S Black shale Polyansky and Reverdatto (2006) T-L M -F-R 280 m 10-70% c S Sand/siltstone Raymond and Murchison (1988) V 50-118.5 m $100-200% a S Shale/silt/limestone Rodriguez Monreal et al (2009) T-Ro-HC V-RE-GC 110-600 m 50-100% a S Black shale Santos et al (2009) T Mi-El 13 m $90% b S Carbonate/ black shale Saxby and Stephenson (1987) TOC-GC-Da 3 m $50% b S Oil shale Simoneit et al (1978Simoneit et al ( , 1981 V-TOC-GC-Da 0.2-15 m 40-50% a ...…”

On the determination of thermal conductivity of sedimentary rocks and the significance for basin temperature history

“…Vitrinite maturation models use the EASY%Ro vitrinite reflectance model developed by Sweeney & Burnham (1990). Our model is described in detail in Fjeldskaar et al (2008). The calculated vitrinite reflectance for the various thermal conductivity models is shown in Figure 20.…”

“…(cf. Fjeldskaar et al 2008). The temperature regime was determined for each of these 14 time slices of the geohistory.…”

Modelling thermal transients from magmatic underplating—an example from the Vøring margin (NE Atlantic)

“…Fjeldskaar et al [10] presented case studies of the thermal impact of sill intrusions in the sediments in the Vøring Basin, and Fjeldskaar et al [9,11] have shown case studies of temperature transients in the sedimentary basin from magmatic underplating. The basis for their study is a backward kinematic modelling tool, creating areabalanced cross-sections in environments with normal or reverse faults.…”