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The [[lithostratigraphy|litho-] and [[chronostratigraphy]] of the [[Mesozoic]] and [[Cenozoic]] sequences of the Hammerfest Basin, as well as the main [[tectonic]] events and main components of the [[petroleum system]] in the area, are shown in [[:file:M114CH10FG03.jpg|Figure 3]]. The main [[reservoir]] rocks in the area, and the only ones considered in this study, are the Early [[Jurassic]] [[sandstone]]s deposited in coastal plain ([[Nordmela Formation]]) and shallow marine ([[Stø Formation]]) environments. These rocks were overlain by the organic poor [[shale]]s of the [[Fuglen Formation]], which separates the Jurassic reservoirs from the main [[source rock]] in the area (Late Jurassic [[Hekkingen Formation]]). The Lower [[Cretaceous]] rocks mainly consist of shales of the [[Knurr formation|Knurr]] and [[Kolje formation]]s and are overlain by the [[Kolmule Formation]], which has a somewhat higher silt content (Mørk et al., 1999<ref name=Morketal1999>Mørk, A., W. K. Dallmann, H. Dypvik, E. P. Johannesen, G. B. Larsen, J. Nagy, et al., 1999, Mesozoic lithostratigraphy, in W. K. Dallmann, ed., Lithostratigraphic lexicon of Svalbard: Review and Recommendations for Nomenclature Use. Upper Paleozoic to Quaternary Bedrock, Norsk Polarinstitutt, Tromsø, p. 127–214.</ref>). This formation is again overlain by a [[Cenomanian]] to [[Campanian]] rock sequence, which consists of condensed calcareous units of the [[Kviting Formation]] in the central Hammerfest Basin and of claystones of the [[Kveite Formation]] elsewhere in the study area. The Kveite, Kviting, and upper part of the Kolmule formations are intersected by polygonal [[fault]]s in parts of the study area, which may have served as [[fluid flow]] pathways and connected [[gas]] from underlying reservoir to the [[Paleocene]] strata of the [[Torsk Formatio]]n (Ostanin et al., 2012<ref name=Ostaninetal2012a />). The Paleocene to [[Eocene]] transition is characterized by an angular [[unconformity]], on top of which [[clinoform]]s reflect prograding [[sediment]]s with shaly and some coarser material intermixed (Knutsen and Vorren, 1991<ref name=Knutsenandvorren1991>Knutsen, S. M., and T. O. Vorren, 1991, Early Cenozoic sedimentation in the Hammerfest Basin: Marine Geology, v. 101, no. 1–4, p. 31–48.</ref>). The [[overburden]] rocks thus mainly consist of shales but with occasional coarser (permeable) layers in distinct [[sequence]]s. About 1 km (0.6 mi) of Cenozoic rocks have been removed from the Hammerfest Basin (Nyland et al., 1992<ref name=Nylandetal1992>Nyland, B., L. N. Jensen, J. Skagen, O. Skarpnes, and T. Vorren, 1992, Tertiary uplift and erosion in the Barents Sea: Magnitude, timing and consequences, in R. M. Larsen, H. Brekke, B. T. Larsen, and E. Talleraas, eds., Structural and tectonic modelling and its application to petroleum geology: Norwegian Petroleum Society Special Publications 1, p. 153–162.</ref>) after maximum burial in [[Oligocene]] to [[Miocene]] times (Doré and Jensen, 1996<ref name=Doreandjensen1996 />). The amount of [[erosion]] increases eastward, with differing suggestions of the timing and amount of individual erosional episodes (Cavanagh et al., 2006<ref name=Cavanaghetal2006>Cavanagh, A. J., R. Di Primio, M. Schenck-Wenderoth, and B. Horsfield, 2006, Severity and timing of Cenozoic exhumation in the southwestern Barents Sea: Journal of the Geological Society of London, v. 163, p. 761–774.</ref>). The top of the eroded rocks, termed the URU, also marks the base of the 100–300-m (328–984-ft)-thick [[Quaternary]] [[glaciogenic]] sediments. The water depth in the area is about 300 m (984 ft).

The [[lithostratigraphy|litho-] and [[chronostratigraphy]] of the [[Mesozoic]] and [[Cenozoic]] sequences of the Hammerfest Basin, as well as the main [[tectonic]] events and main components of the [[petroleum system]] in the area, are shown in [[:file:M114CH10FG03.jpg|Figure 3]]. The main [[reservoir]] rocks in the area, and the only ones considered in this study, are the Early [[Jurassic]] [[sandstone]]s deposited in coastal plain ([[Nordmela Formation]]) and shallow marine ([[Stø Formation]]) environments. These rocks were overlain by the organic poor [[shale]]s of the [[Fuglen Formation]], which separates the Jurassic reservoirs from the main [[source rock]] in the area (Late Jurassic [[Hekkingen Formation]]). The Lower [[Cretaceous]] rocks mainly consist of shales of the [[Knurr formation|Knurr]] and [[Kolje formation]]s and are overlain by the [[Kolmule Formation]], which has a somewhat higher silt content (Mørk et al., 1999<ref name=Morketal1999>Mørk, A., W. K. Dallmann, H. Dypvik, E. P. Johannesen, G. B. Larsen, J. Nagy, et al., 1999, Mesozoic lithostratigraphy, in W. K. Dallmann, ed., Lithostratigraphic lexicon of Svalbard: Review and Recommendations for Nomenclature Use. Upper Paleozoic to Quaternary Bedrock, Norsk Polarinstitutt, Tromsø, p. 127–214.</ref>). This formation is again overlain by a [[Cenomanian]] to [[Campanian]] rock sequence, which consists of condensed calcareous units of the [[Kviting Formation]] in the central Hammerfest Basin and of claystones of the [[Kveite Formation]] elsewhere in the study area. The Kveite, Kviting, and upper part of the Kolmule formations are intersected by polygonal [[fault]]s in parts of the study area, which may have served as [[fluid flow]] pathways and connected [[gas]] from underlying reservoir to the [[Paleocene]] strata of the [[Torsk Formatio]]n (Ostanin et al., 2012<ref name=Ostaninetal2012a />). The Paleocene to [[Eocene]] transition is characterized by an angular [[unconformity]], on top of which [[clinoform]]s reflect prograding [[sediment]]s with shaly and some coarser material intermixed (Knutsen and Vorren, 1991<ref name=Knutsenandvorren1991>Knutsen, S. M., and T. O. Vorren, 1991, Early Cenozoic sedimentation in the Hammerfest Basin: Marine Geology, v. 101, no. 1–4, p. 31–48.</ref>). The [[overburden]] rocks thus mainly consist of shales but with occasional coarser (permeable) layers in distinct [[sequence]]s. About 1 km (0.6 mi) of Cenozoic rocks have been removed from the Hammerfest Basin (Nyland et al., 1992<ref name=Nylandetal1992>Nyland, B., L. N. Jensen, J. Skagen, O. Skarpnes, and T. Vorren, 1992, Tertiary uplift and erosion in the Barents Sea: Magnitude, timing and consequences, in R. M. Larsen, H. Brekke, B. T. Larsen, and E. Talleraas, eds., Structural and tectonic modelling and its application to petroleum geology: Norwegian Petroleum Society Special Publications 1, p. 153–162.</ref>) after maximum burial in [[Oligocene]] to [[Miocene]] times (Doré and Jensen, 1996<ref name=Doreandjensen1996 />). The amount of [[erosion]] increases eastward, with differing suggestions of the timing and amount of individual erosional episodes (Cavanagh et al., 2006<ref name=Cavanaghetal2006>Cavanagh, A. J., R. Di Primio, M. Schenck-Wenderoth, and B. Horsfield, 2006, Severity and timing of Cenozoic exhumation in the southwestern Barents Sea: Journal of the Geological Society of London, v. 163, p. 761–774.</ref>). The top of the eroded rocks, termed the URU, also marks the base of the 100–300-m (328–984-ft)-thick [[Quaternary]] [[glaciogenic]] sediments. The water depth in the area is about 300 m (984 ft).

The [[hydrocarbon]]s were largely sourced from the deep [[Cretaceous]] [[Tromsø Basin]] to the west, although minor contributions from locally mature [[source rock]]s above the deeper structures may also have occurred. The [[trap]] filling mainly occurred from Middle Cretaceous times to the time of maximum burial. The leakage that resulted in the present [[underfill]]ing of traps occurred after this time. [[Gas]] exsolution from [[oil]] and pore water and gas expansion due to fluid pressure decrease during erosion also resulted in increased gas volumes in the traps and contributed to [[overpressure]] generation here (Hermanrud et al., 2013<ref name=Hermanrudetal2013bHermanrud, C., J. M. Venstad, J. Cartwright, L. Rennan, K. Hermanrud, and H. M. Nordgård Bolås, 2013b, Consequences of water level drops for soft sediment deformation and vertical fluid leakage: Mathematical Geosciences, v. 45, no. 1, p. 1–30.</ref>). Hermanrud et al. (2014<ref name=Hermanrudetal2014 />) used the observation that the [[gas-water]] contacts coincide with the depth of the top [[reservoir]] surface at [[fault]] intersections or [[relay ramp]]s as a main argument for these positions as being leakage locations. This suggestion implies that the leakage took place late in the erosional history or after it.

The [[hydrocarbon]]s were largely sourced from the deep [[Cretaceous]] [[Tromsø Basin]] to the west, although minor contributions from locally mature [[source rock]]s above the deeper structures may also have occurred. The [[trap]] filling mainly occurred from Middle Cretaceous times to the time of maximum burial. The leakage that resulted in the present [[underfill]]ing of traps occurred after this time. [[Gas]] exsolution from [[oil]] and pore water and gas expansion due to fluid pressure decrease during erosion also resulted in increased gas volumes in the traps and contributed to [[overpressure]] generation here (Hermanrud et al., 2013<ref name=Hermanrudetal2013b<Hermanrud, C., J. M. Venstad, J. Cartwright, L. Rennan, K. Hermanrud, and H. M. Nordgård Bolås, 2013b, Consequences of water level drops for soft sediment deformation and vertical fluid leakage: Mathematical Geosciences, v. 45, no. 1, p. 1–30.</ref>). Hermanrud et al. (2014<ref name=Hermanrudetal2014 />) used the observation that the [[gas-water]] contacts coincide with the depth of the top [[reservoir]] surface at [[fault]] intersections or [[relay ramp]]s as a main argument for these positions as being leakage locations. This suggestion implies that the leakage took place late in the erosional history or after it.

==See also==

==See also==