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1 Department of Arctic Geology, University Centre, Svalbard, Norway | 2 Volcanic Basin Petroleum Research, Norway | 3 Department of Geology & Petroleum Geology, University of Aberdeen, UK | 4 Centre for Earth Evolution & Dynamics, University

of Oslo, Norway | 5 Department of Earth Sciences, VU University Amsterdam, the Netherlands | 6 Department of Earth Science,

University of Bergen, Norway | 7 Department of Geology, University of Tromsø, Norway | 8 Physics of Geological Processes,

University of Oslo, Norway | 9 DougalEarth, UK

Corresponding author, E-mail: Kim Senger, kim.senger@unis.no

DOI: xxx

world (Schutter, 2003b). Many of these represent non-com-mercial accumulations, but there are important exceptions. For instance, hydrocarbons are currently produced commercially from fractured igneous intrusions in the Argentinian Neuquén basin (Figure 3). These atypical reservoirs, such as the Los Cavaos field, usually host up to 25 million barrels of recoverable oil per field, and are characterized by rapid initial production rates of up to 10,000 barrels/day (Witte et al., 2012). Besides forming reservoirs, igneous intrusions may be emplaces at a wide range of burial depths, affecting all basic elements of the petroleum system in a broader scope than merely feeding extrusive lava flows or other effusive volcanic deposits that become part of the basin fill. Some volcanic basins, such as the Rockall Trough-Vøring-Møre system along the UK-Norway continental margin, are currently being targeted for their hydrocarbon potential. In other volcanic basins, such as the Faroe-Shetland basin, significant discoveries have already been made, with the discovery of the Rosebank, Laggan and Tormore fields (e.g., Schofield et al., 2015). In these settings, igneous intrusions directly influence all or several aspects of the petroleum system, including charge, seal, trap and reservoir (e.g., Jerram, 2015). In this article, we provide an

IntroductionEmplacement of magma has led to the development of extensive networks of igneous intrusions in the subsurface of many sedi-mentary basins worldwide (Figure 1), particularly in extensional basins and on passive margins. These intrusions commonly occur as (1) layer-parallel and transgressive sills, (2) saucer-shaped intrusions, (3) layer-discordant sub-vertical dykes and (4) local-ized volcanic centers (e.g., Jerram and Bryan, 2015). Figure 2 provides a generalized cross section through a volcanic basin highlighting some of the key terminology and relationships of the igneous rocks with the host basin. Sills are tabular igneous intrusions that are dominantly parallel to the host rock bedding and sub-horizontal. Dykes represent magma sheets crosscutting the strata, and are generally sub-vertical. Both dykes and sills form contact metamorphic aureoles caused by localized heating of the adjacent host rock. Moreover, in addition to subsurface emplacement, significant volumes of magma may have reached the surface, resulting in volcanic activity with significant volumes of extrusive lava flows covering the volcanic plumbing system (e.g., Jerram and Widdowson, 2005). There are several examples of hydrocarbon fields associated with igneous rocks around the

AbstractIgneous intrusions feature in many sedimentary basins where hydrocarbon exploration and production is continuing. Due to distinct geophysical property contrasts with siliciclastic host rocks (e.g., higher V

p, density and resistivity

than host rocks), intrusions can be easily delineated within data sets including seismic and CSEM profiles, provided igneous bodies are larger than the detection limit of the geophysical methods. On the other hand, igneous bodies affect geophysical imaging in volcanic basins. Recent analyses of 3D seismic data, supported by field observations and lab-based experiments, have provided valuable insights into the prevailing geometries of intrusions, i.e. (1) layer-discordant dykes, (2) layer-parallel sills and (3) saucer-shaped intrusions. Where emplaced, intrusive bodies affect all five principal components of a given petroleum system: (1) Charge, (2) Migration, (3) Reservoir, (4) Trap and (5) Seal. Magmatic activity may positively or adversely affect any of these individual components, for instance by locally enhancing maturation within the thermal aureoles, typically 30-250% of the intrusion thickness, or by causing regional overmaturation. Site-specific evaluations, including the timing and duration of the magmatic event are needed to evaluate the overall effect of intrusions on a given sedimentary basin’s petroleum system, and these are highlighted by case studies from different volcanic basins.

Kim Senger1, John Millett2,3, Sverre Planke2,4, Kei Ogata5, Christian Haug Eide6, Marte Festøy7, Olivier Galland8 and Dougal A. Jerram9,4

Effects of igneous intrusions on the petroleum system: a review

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and Planke et al. (2015) report a strong contrast in P-wave velocity within an igneous intrusion (5.5-6.5 km/s) compared to the surrounding host rock (ca. 3 km/s). These high velocities within the intrusions produce characteristic velocity profiles that are different to the extrusive volcanic facies types (Nelson et al., 2009). Nonetheless, many thin sills falls below the seismic resolution (Schofield et al., 2015). In addition, the complex and often discordant geometry of igneous bodies presents significant challenges to imaging both in seismic data (e.g., Anell et al., 2016; Eide et al., 2016) and in resistivity mapping (e.g., Planke et al., 2015). Thick intrusive complexes or effusive lavas, for instance, often lead to a significant loss of seismic imaging below (i.e. sub-basalt imaging; e.g., Gallagher and Dromgoole, 2007). Significant uncertainties may therefore be introduced in petroleum systems affected by magmatism. Offshore mapping of igneous intrusions, particularly when using 3D seismic, offers high-resolution maps of the intrusive body geometry, and has been instrumental for mapping of saucer-shaped intrusions (e.g., Hansen and Cartwright, 2006; Schofield et al., 2015). Resistivity derived from CSEM data provides constraints on the transverse resistance (i.e. resistivity × thickness) of the sills, and, particular-ly when coupled with MT data and other remote sensing data, can provide a good thickness estimate of basalt sequences (Hautot et al., 2007; Johansen and Gabrielsen, 2015; Panzner et al., 2016). Fieldwork, on the other hand, provides the necessary ground truth to link the geophysical measurements to exposed igneous intrusions where critical details (e.g., contact metamorphic aure-oles, fracturing patterns, magma flow indicators and sub-seismic geometries) are discernable and quantifiable (e.g., Schofield et al., 2016). Where wells penetrate igneous intrusions, convention-

updated review on the effects that igneous intrusions may have on the petroleum system, summarizing the current state-of-the-art and discussing newly acquired and published, geophysical- and outcrop-based datasets.

Mapping and characterizing igneous intrusionsIgneous intrusions can be studied both onshore, using traditional field mapping and geophysical techniques, as well as offshore, normally using remote geophysical methods in combination with well data. Mapping of igneous intrusions by remote sensing methods has been recently reviewed by Planke et al. (2015). In sedimentary basins, the large difference in elastic and electric properties of igneous rocks compared to the sedimentary host rock facilitates their identification using both elastic (i.e. seismic) and electric (e.g., controlled-source electromagnetic, magnetotel-luric) techniques. For instance, Smallwood and Maresh (2002)

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the North Atlantic (Rohrman, 2007; Schofield et al., 2015), the Møre-Vøring basins offshore mid-Norway (Aarnes et al., 2015), the Sverdrup Basin of Arctic Canada (Jones et al., 2007), the Siberian Tunguska Basin (Svensen et al., 2009) and the Brazilian basins such as the Parnaiba basin (Miranda et al., 2016).

The different effects of intrusions on the petroleum system are summarized in Figure 5, and listed in Table 1. In some cases, such as the formation of migration shadows, the igneous intrusions influence the conventional petroleum system. In other cases, such as when igneous intrusions form reservoirs or seals, intrusions can directly represent an element of the petroleum system.

ChargeA sufficiently thick and organic rich source rock is a prerequisite to enable hydrocarbons to be generated. In a ‘traditional’ petrole-um system, temperature increase associated with burial primarily drives source rock maturation and allows the generated hydro-carbons to migrate upwards along paths of highest permeability and become trapped. Both the timing, especially with respect to generation of traps, and the duration of optimal conditions for hydrocarbon generation are important to calculate the total potential of a given source rock in a given basin. This is normally measured by examining the geo-history of the basin concerned, using burial history curves, which in volcanic basins can be mod-ified by the rapid burial of the basin through the accumulation of thick erupted volcanic units (e.g., Schofield et al., 2016).

In a volcanic basin where significant intrusions are present, maturation is further influenced both by the local presence of hot igneous bodies and an enhanced regional heat flow. Pioneering work on the effect of igneous intrusions on maturation was conducted in the coal-bearing Carboniferous succession of the Midland Valley of Scotland (e.g., Murchison and Raymond, 1989; George, 1992). Murchison and Raymond (1989) conclude, for instance, that a regional lateral trend of increasing coalifica-tion from east to west is primarily related to a thicker package of volcanic rocks towards the western edge of the graben. Bishop and Abbott (1995) investigate vitrinite reflectance near several relatively thin (0.9 m) dykes in northwest Scotland, suggesting a proportionality of dyke thickness with the extent of the

al wireline logs may be used to define both the sills’ boundaries and the associated contact metamorphic aureole (Aarnes et al., 2015; Delpino and Bermúdez, 2009). Basaltic intrusions typically exhibit a low gamma ray, high velocity and high resistivity, with local fluctuations owing to e.g., compositional differences, alteration or fracturing (Figure 4).

Intrusions and the petroleum systemIn this article, we follow the definition of Magoon and Dow (1994), stating that a petroleum system is ‘a natural system that encompasses a pod of active source rock and all related oil and gas and which includes all the geologic elements and processes that are essential if a hydrocarbon accumulation is to exist’. Petroleum systems are commonly distinguished on the basis of a common source and reservoir rock; several petroleum plays may exist within any given petroleum system. A petroleum system comprises (1) a source rock subject, over sufficient time, to conditions leading to hydrocarbon generation (i.e. charge), (2) pathways for the generated hydrocarbons to be expelled from the source rock and move to a reservoir rock (i.e. primary and sec-ondary migration, respectively), (3) a porous and permeable rock to serve as a reservoir for the hydrocarbons and (4) an enclosing structure (i.e. trap) with (5) low permeability extremities (i.e. lateral and top seal). Igneous intrusions may affect any of these five main petroleum system elements.

While hydrocarbon accumulations are associated with igne-ous rocks in more than 100 countries across the globe (Fig 1; Schutter, 2003b), only a handful of such basins have to date been subject to commercial production. Examples include the Mesozoic-Cenozoic basins of eastern China (Liu et al., 2013; Wu et al., 2006), oil-producing sills of the Neuquén Basin in Argentina (Rodriguez Monreal et al., 2009; Witte et al., 2012), tuffaceous reservoirs in West Java (Farooqui et al., 2009) and intrusion hosted reservoirs in Thailand (e.g., Schutter, 2003b). In addition, magmatic activity has, primarily through enhanced source rock maturation and compartmentalization, played a key role in the petroleum systems of many basins including the onshore-offshore Taranaki Basin in New Zealand (Stagpoole and Funnell, 2001), the Faroe-Shetland and Rockall Trough Basins in

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Table 1 xxx

Positive effect Key references Negative effect Key referencesPe

trol

eum

Sys

tem

Ele

men

ts

Charge Locally enhanced maturation generates hydrocarbons in immature basins.

Stagpoole and Funnel (2001)

“Overcooking” of source rocks in direct contact with intrusions leads to loss of TOC and any generated hydrocarbons.

Mørk and Bjorøy (1984), Rohrmann (2007)

Regional heat flow increase from extensive magmatism may lead to enhanced maturity regionally.

Mørk and Bjorøy (1984) Intrusions may compartmentalize the source rock, forming barriers for hydrocarbon migration to reservoirs.

Rateau et al. (2013), Delpino and Bermudez (2009), Holford et al. (2013)

Extensive global-scale volcanism may contribute to temporary anoxia, and thus indirectly better quality source rocks.

Zimmerle (1995) Ashfall dilutes organic-rich source rocks, leading to lower TOC and lower source rock quality.

Moore et al. (2011)

Subaerial volcanics generate organic-rich lacustrine oil-prone organic material.

Khadkikaer et al. (1999)

Hydrocarbon generation at hydrothermal vent complexes.

Simoniet (1985)

Stacked sills are likely to enhance maturation, and thus either contribute to generate hydrocarbons or destroy them.

Aarnes et al. (2011), Rodriguez Monreal et al. (2009)

Migration Intrusions may channel fluid flow (e.g., hydrocarbons) towards traps.

Rateau et al. (2013) Intrusions may channel hydrocarbons away from traps, and generate shadow zones.

Rateau et al. (2013)

Igneous activity dramatically enhances the effectivess of migration by converting groundwater to a supercritical state.

Simoniet (1994)

Reservoir Fractured intrusions may act as an unconvetional reservoir, with hydrocarbons primarily confined to the fracture network.

Gudmundsson and Løtveit (2012), Wu et al. (2006), Witte et al (2012)

Contact metamorphism will locally lead to porosity reduction if reservoir sandstone is intruded.

Aarnes et al. (2011)

Intrusions will compartmentalize a reservoir, making production challenging.

Eide et al. (2016)

Trap Impermeable intrusions can act as structural traps (e.g., christmas-tree laccoliths).

Schutter (2003a) Intrusions may destroy conventional traps, particularly if magma intrudes along pre-existing fault system.

Rateau et al. (2013), Schofield et al. (2015)

Intrusion emplacement may generate traps in the overburden (e.g., forced folds).

Hansen and Cartwright (2006b), Jackson et al. (2013)

Traps related to intrusions are produced independent of regional tectonics.

Schutter (2003a)

Seal Intrusions may act both as a top and lateral seal.

Wu et al. (2006), Thomaz Filho et al. (2008)

Permeable intrusions (i.e. fractured) may act as a seal by-pass system across intrusion-host rock interface.

Senger et al. (2013)

Sealing properties of intrusions are unpredictable, being primarily controlled by the fracture network properties.

Senger et al. (2015)

Geophysical Imaging

Given the high acoustic and electric contrast to host rocks, intrusions are relatively easily imaged using seismic or CSEM data.

Planke et al. (2015) Igneous intrusions will mask deposits and structures below them due to reflection of seismic energy, making seismic hard to interpret.

Maresh et al. (2006), Davison et al. (2010), Gallagher and Dromgoole (2007)

Highly resistive igneous intrusions can potentially be misinterpreted as hydrocarbon-bearing reservoirs on CSEM data.

Suffert et al. (2009)

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may also compartmentalize the source rocks (Holford et al., 2013), as sills are preferentially emplaced within major lithologic boundaries such as regional mudstone intervals (e.g., Eide et al., 2016). Compartmentalization of the source rock is likely to reduce migration efficiency of the generated hydrocarbons or, in some cases, even prevent generated hydrocarbons from migrating out of the source rock interval.

MigrationThe potential regional impact of igneous intrusions on hydrocar-bon migration has been well documented in Western Australia (Holford et al., 2013), the Brazilian basins (Thomaz Filho et al., 2008) and the Faroe-Shetland Basin (Rateau et al., 2013). In essence, igneous intrusions may both establish new migration pathways if they are fractured and permeable, or they can act as fluid flow barriers if they are mineralized and impermeable (Figure 6). These attributes of igneous intrusions to act either as conduits or barriers to fluid flow, or even as both, are linked to the origin of the natural fracture network (Senger et al., 2015). For a particular sill, the nature of fracturing will primarily be related to the overall intrusion geometry, which influences the geometry of the cooling joints, and post-cooling tectonism. Furthermore, any additional fractures associated with the emplacement of the intrusion will modify the fracture networks in the host rock either side of the intrusion. The composition and cooling rate of the magma, as well as emplacement depth and host rock permeability will also influence the nature of the fracture network. Structurally complex zones, such as at dyke-sill junctions, sill inflection points and intrusion-host rock interfaces, are typically associated with enhanced fracturing and represent the most permeable zones (Chevallier et al., 2001). Knowledge of hydrothermal fluid

thermal alteration aureole (i.e. ca. 70% of the dyke thickness). Contact metamorphic processes, leading to release of pore water, organic carbon and mineral-bound CO2 and H2O (e.g., Aarnes et al., 2010), act on the source rock, essentially accelerating hydrocarbon maturation. In near-intrusion zones, this process leads to extensive overmaturation, causing the overcooking of the source rocks. Aarnes et al. (2010) review the existing literature and conclude that the aureole thickness varies within 30-250% of the sill thickness. At great distances from intrusions, the heating effect will be reduced and perhaps limited to the convective heat dissipation (Iyer et al., 2013) by hydrothermal fluid migration which may contribute to enhanced regional heat flow where multiple intrusions are present. In this scenario, igneous activity can generate the heat required to mature an otherwise immature source rock. Even relatively lean source rock intervals, such as the Cretaceous (c. 1 wt% organic carbon) of the Utgard High offshore mid/Norway, may generate significant volumes of gas owing to the large volume affected by the intrusions (Aarnes et al., 2015). Clearly, the timing and duration of the magmatic activity, as well as the state of the source rock (i.e. immature, mature or overmature), will determine whether a given basin will experience positive or negative effects on basin-scale maturation.

Jones et al. (2007), on the basis of 1D numerical modelling, concluded that Early Cretaceous sill intrusions in the Canadian Sverdrup Basin led to enhanced generation of hydrocarbons from previously immature source rocks. Wang et al. (2012) conducted a similar study of the petroleum system in the eastern China Bohai Bay Basin, concluding that igneous intrusions locally enhanced and accelerated the hydrocarbon generation within the source rocks by up to 100 m from the approximately 100 m thick sills. Apart from direct heating effects, igneous intrusions

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folding of host rock overlying intrusions (Jackson et al., 2013) may also generate higher permeability fracture-related pathways away from the intrusion itself.

ReservoirIgneous intrusions, and their effusive counterparts, may form reservoirs in their own right. The primary matrix porosity and permeability of igneous rocks is generally very low, but significant porosity and permeability may develop owing to frac-turing, zones with vesicles, and in hydrothermally altered zones. Schutter (2003a) classifies these into three porosity types: (1) primary porosity, usually intergranular or vesicular, (2) secondary porosity, associated primarily with hydrothermal alteration and (3) fracture porosity. In some reservoirs, such as in the Chinese Liaohe basin, vesicular basalt and andesite may have local poros-ities of up to 30-50% (Chen et al., 1999). Fracture porosity is sometimes included within secondary porosity, an all-encompass-ing term referring to pore space that resulted from hydrothermal alteration, dissolution by groundwater and tectonic stress (Chen et al., 1999). This is obvious, as fractures often connect primary vesicular pores with dissolution pores, and are usually exploited by highly reactive hydrothermal fluids. In basins exhibiting a complex geological history with significant post-magmatism tectonic events, additional tectonic fracturing may significantly enhance the connectivity of the fracture network.

Igneous intrusions with commercially exploitable hydrocar-bon reservoirs have been documented in eastern China (Wu et al., 2006), the Argentinian Neuquén Basin (Delpino and Bermúdez, 2009; Witte et al., 2012) and other basins worldwide (Farooqui et al., 2009; Schutter, 2003b and references therein). In these examples, igneous bodies predominantly intrude organic-rich shales, enhancing local maturation of organic matter and hosting generated hydrocarbons in their natural fracture network. Such fracture networks are predominantly developed during cooling and associated thermal contraction, often exhibited as regular columnar-jointing patterns oriented perpendicular to the intrusion contacts (i.e. cooling joints: e.g., Kattenhorn and Schaefer, 2008). Fractures parallel to intrusion boundaries, and post-intrusion tectonic fractures, are also common (e.g., Senger et al., 2015). In addition, hydrocarbon accumulations in igneous rocks may be related to breccia-type reservoirs at the top of volcanic stocks, zones of chemically or mechanically altered intrusions and zones

activity, post-emplacement diagenetic processes and tectonism will provide information on whether a specific fracture network is permeable (i.e. open, inter-connected fractures) or impermeable (i.e. cemented or tight fractures).

The geometry of the igneous plumbing system will also influence the migration routes, with layer-discordant dykes acting as seal-bypass systems in some settings (e.g., Thomaz Filho et al., 2008), and generating migration shadows elsewhere. Numerous studies have demonstrated the relationships of igneous intrusions and pre-existing fault systems, illustrating that many fault zones act as weakness zones exploited by propagating magma (e.g., Magee et al., 2013). As faults often generate structural traps, this has direct implications both on the destruction of such traps by the intrusions themselves, and the possible development of permeable zones.

Igneous intrusions, in a process similar to sandstone intru-sions (i.e. injectites) or salt diapirs, can breach the integrity of the overlying seal (Cartwright et al., 2007) if they penetrate the reservoir-cap rock interface. This process involves both the initial puncturing of the seal and transmission of fluids (i.e. magma) and the subsequent permeability contrast in the intrusion and the surrounding host rock. Mechanical processes related to forced

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propagated through sandstone host rock (Eide et al., 2016). These can lead to sub-seismic baffles to fluid flow in reservoirs and adversely affect the overall production potential.

TrapIgneous intrusions may form hydrocarbon traps, both directly and indirectly (Figure 7). Similarly to sealing faults, impermeable intrusions such as dykes or stocks cross-cutting stratigraphy, may generate numerous traps for migrating hydrocarbons. In addition, forced folds above laccoliths, saucer-shaped sills or stocks may form significant four-way dip closures in the overlying sediments (e.g., Jackson et al., 2013). It is worth mentioning that in a given basin, intrusion-related traps are not necessarily related to the overall tectonic regime, and are more locally controlled by igneous processes and subsequent geometries of intrusive bodies. In this framework, a different exploration strategy must be employed when targeting such traps. On the other hand, intrusions may also destroy pre-existing traps, deeply modifying the geologic framework with the processes described above. This is especially true for fault-related structural traps, as magma commonly exploits fault zones during its migration (e.g., Magee et al., 2013; Schofield et al., 2016).

SealMost igneous intrusions, being free of alterations and fracturing, are impermeable and thus represent good sealing rocks (e.g., Wu et al., 2006). Impermeable intrusions may act both as a lateral and top seal for hydrocarbon accumulations (Thomaz Filho et al., 2008). Conversely, permeable or semi-permeable intrusions, may act as seal-bypass systems (Cartwright et al.,

of enhanced fracturing along intrusions’ boundaries (e.g., Wu et al., 2006).

In settings where the hydrocarbons are hosted in convention-al, i.e. carbonate or sandstone, reservoirs, intrusions will mainly affect the geologic framework through contact metamorphic aureoles. These zones of enhanced physical-chemical alteration will typically locally lead to reduced porosity and often increased fracturing typically oriented perpendicular and parallel to the intrusion-host rock contacts. Quantifying the exact porosity and permeability loss is challenging, as it is strongly dictated by the initial host rock properties and the interaction of conductive and convective heat dissipation. Smallwood & Harding (2004), for instance, report on a sill drilled in the Faroe-Shetland basin which does not appear to affect the moderate (11-13%) porosity reservoir sandstone that lies on the expected regional porosity-depth trend, though the low (3.6 mD) mean permea-bility of the reservoir sandstone is thought to be associated with intrusion-related hydrothermal alteration. Dutrow et al. (2001) model the thermo-chemical aureole processes associated with an 11 m thick dyke intruded into interbedded carbonate mudstones and siltstones in Louisiana, suggesting that local permeability reduction after mineral precipitation may be mitigated over time as fluid flow pathways change dynamically. It follows that case-by-case studies are required to adequately quantify a given intrusion’s effect on the reservoir properties. On a more regional scale, the intrusions, particularly if layer-discordant, are expected to compartmentalize the reservoir. This has implications on pres-sure build up in the hydrocarbon column along with production and volumetric calculations. Minor (meter-scale) intrusions often occur parallel and in close proximity to intrusions which

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and low-angle clinoforms: A case study of the Triassic successions on Edgeøya, NW Barents Shelf. Marine and Petroleum Geology, 77, 625-639.

Bishop, A.N. and Abbott, G.D. [1995]. Vitrinite reflectance and molecular geochemistry of Jurassic sediments: the influence of heating by Tertiary dykes (northwest Scotland). Organic Geochemistry, 22(1), 165-177.

Bryan, S.E. and Ferrari, L. [2013]. Large igneous provinces and silicic large igneous provinces: Progress in our understanding over the last 25 years. Geological Society of America Bulletin, 125(7-8), 1053-1078.

Cartwright, J., Huuse, M. and Aplin, A. [2007]. Seal bypass systems. AAPG bulletin, 91(8), 1141-1166.

Chen, Z., Yan, H., Li, J., Zhang, G., Zhang, Z. and Liu, B. [1999]. Relationship between Tertiary volcanic rocks and hydrocarbons in the Liaohe Basin, People’s Republic of China. AAPG bulletin, 83(6), 1004-1014.

Chevallier, L., Goedhart, M. and Woodford, A.C. [2001]. The influences of dolerite sill and ring complexes on the occurrence of ground-water in Karoo fractured aquifers: a morpho-tectonic approach. Water Resource Commission Reports, WRC Report No. 937/1/01, 165.

Davison, I., Stasiuk, S., Nuttall, P. and Keane, P. [2010]. Sub-basalt hydrocarbon prospectivity in the Rockall, Faroe-Shetland and Møre basins, NE Atlantic. In: B.A. Vining and S.C. Pickering (Editors), Petroleum Geology: From Mature Basins to New Frontiers - Proceed-ings of the 7th Petroleum Geology Conference. Geological Society, London, 1025-1032.

Delpino, D.H. and Bermúdez, A.M. [2009]. Petroleum systems including unconventional reservoirs in intrusive igneous rocks (sills and laccoliths). The Leading Edge, 28(7), 804-811.

Dutrow, B.L., Travis, B.J., Gable, C.W. and Henry, D.J. [2001]. Coupled heat and silica transport associated with dike intrusion into sedimen-tary rock: Effects on isotherm location and permeability evolution. Geochimica et Cosmochimica Acta, 65(11), 3749-3767.

Eide, C.H., Schofield, N., Jerram, D.A. and Howell, J.A. [2016]. Basin-scale architecture of deeply emplaced sill complexes: Jameson Land, East Greenland. Journal of the Geological Society.

Farooqui, M., Hou, H., Li, G., Machin, N., Neville, T., Pal, A., Shrivastva, C., Wang, Y., Yang, F. and Yin, C. [2009]. Evaluating volcanic reservoirs. Oilfield Review, 21(1), 36-47.

Gallagher, J.W. and Dromgoole, P.W. [2007]. Exploring below the basalt, offshore Faroes: a case history of sub-basalt imaging. Petroleum Geoscience, 13(3), 213-225.

George, S.C. [1992]. Effect of igneous intrusion on the organic geochem-istry of a siltstone and an oil shale horizon in the Midland Valley of Scotland. Organic Geochemistry, 18(5), 705-723.

Gudmundsson, A. and Løtveit, I.F. [2012]. Sills as fractured hydrocarbon reservoirs: examples and models. In: G.H. Spence, J. Redfern, R. Aguilera, T.G. Bevan, J.W. Cosgrove, G.D. Couples and J.M. Daniel (Editors), Advances in the Study of Fractured Reservoirs, Geological Society of London Special Publication #374. Geological Society of London, London, 21.

Hansen, D.M. and Cartwright, J. [2006a]. Saucer-shaped sill with lobate morphology revealed by 3D seismic data: implications for resolving a shallow-level sill emplacement mechanism. Journal of the Geolog-ical Society, 163(3), 509-523.

2007). Alteration of igneous bodies is often thought to reduce any porosity/permeability. However, in active hydrothermal systems, significant secondary porosity can be generated. Determining the sealing properties of a given intrusion is therefore difficult, given the complex variability in magma composition, intrusion geometry, host rock properties and fracture network attributes along the intrusion-host rock interface must be assessed on a case by case basis.

ConclusionsIn this contribution we have provided a brief review of the numer-ous ways in which igneous intrusions can influence the entire petroleum system, including the charge, migration, reservoir, trap and seal. All of these individual petroleum system elements may both be positively and negatively affected by igneous activity. The timing of magmatism, particularly with respect to source rock maturity, determines to a large degree how a particular basin will be affected in terms of hydrocarbon production potential. We conclude that, while igneous intrusions are often expected to have detrimental effects on a petroleum system, their positive aspects should also be appraised, especially in immature basins. This is perhaps best summed up by considering the igneous intrusions currently producing commercial hydrocarbon volumes in Argen-tina, Japan, Thailand and China, among others. Figure 8 provides a synthesis of the current understanding of igneous-related petroleum systems in volcanic margins, and will hopefully assist in the systematic exploration and production of these resources.

AcknowledgementsThis contribution is the result of fruitful collaboration between the MIMES, VMAPP, Trias North and ARCEx projects partially funded by the Research Council of Norway and industry partners. Wireline data presented in Figure 4 was accessed through the DISKOS database, made available to the public domain by the Norwegian Petroleum Directorate. Jerram and Planke are partly supported by the Research Council of Norway through its Centre of Excellence funding scheme (project nr. 223272). We would like to sincerely thank Schlumberger Software for the provision of academic licences for the Petrel software, Mark Mulrooney for language editing and two anonymous reviewers for constructive comments.

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