Flemming G. Christiansen

Oleanane or lupane? Reappraisal of the presence of oleanane in Cretaceous-Tertiary oils and sediments

Nonpolar GC-columns are normally used for GC–MS analysis of saturate fractions from crude oils. Under these conditions lupane coelutes with oleananes and some minor C30 compounds of non-terrigenous origin having lupane-like mass spectra. Because any peak eluting fractionally earlier than 17α,21β(H)-hopane in the m/z 191 mass chromatogram is routinely assigned to oleanane, the presence of lupane may sometimes have been overlooked. Lupane and oleananes are easily separated using reverse phase HPLC. Triterpane concentrates from 10 crude oils known to contain oleananes were HPLC-separated. Lupane was unambiguously identified in six of the oils by full-scan GC–MS analysis of fractions having the HPLC-retention time of authentic lupane. GC-separation of lupane and oleananes is possible using polar GC-columns having a polyethylene glycol stationary phase [Organic Geochemistry, 23 (1995) 21], allowing estimation of the lupane/(lupane+oleanane) ratio. High ratios were measured in the Marraat oil, West Greenland (0.8) and the Amauligak oil from the Beaufort–Mackenzie Delta (0.26). The results suggest that lupane may be more frequently occurring than previously thought, and that this compound is preferably associated with high latitude samples. High concentrations of 28-nor- and 24,28-bisnortriterpanes (oleananes, lupanes and taraxastanes) were detected in the Marraat oil.

Oil seepage onshore West Greenland: evidence of multiple source rocks and oil mixing

Widespread oil seepage and staining are observed in lavas and hyaloclastites in the lower part of the volcanic succession on northwestern Disko and western Nuussuaq, central West Greenland. Chemical analyses suggest the existence of several petroleum systems in the underlying Cretaceous and Paleocene fluvio–deltaic to marine sediments. Seepage and staining commonly occur within vesicular lava flow tops, and are often associated with mineral veins (mostly carbonates) in major fracture systems. Organic geochemical analyses suggest the existence of at least five distinct oil types: (1) a waxy oil which, on the basis of the presence of abundant angiosperm biological markers, is interpreted as generated from Paleocene mudstones (the ‘Marraat type’); (2) a waxy oil, probably generated from coals and shales of the Cretaceous Atane Formation (the ‘Kuugannguaq type’); (3) a low to moderately waxy oil containing 28,30-bisnorhopane, and abundant C 27 -diasteranes and regular steranes (the ‘Itilli type’), possibly generated from presently unknown Cenomanian–Turonian marine mudstones; (4) a low wax oil of marine, possibly lagoonal/saline lacustrine origin, containing ring-A methylated steranes and a previously unknown series of extended 28-norhopanes (the ‘Eqalulik type’); (5) a waxy oil with biological marker characteristics different from both the Kuugannguaq and Marraat oil types (the ‘Niaqornaarsuk type’), probably generated from Campanian mudstones. The presence of widespread seepage and staining originating from several source rocks is encouraging for exploration in basins both on- and offshore western Greenland, where the existence of prolific source rocks has previously been the main exploration risk.

Depositional history and petroleum geology of the Carboniferous to Cretaceous sediments in the northern part of East Greenland

Major depositional phases of subsidence and basin fill occurred in northern East Greenland during the latest Devonian–earliest Carboniferous, Late Carboniferous, Late Permian–earliest Triassic, mid-Jurassic-earliest Cretaceous, and mid-Cretaceous, and a total of 5-6 km of sediment accumulated. These phases were followed by a phase of Tertiary volcanism and a subsequent period of uplift. Potential source rocks include oil-prone, Upper Carboniferous lacustrine shales, oil-prone Upper Permian marine shales, and gas-prone Upper Jurassic marine shales. The shales are generally immature in outcrop with the exception of areas surrounding larger Tertiary intrusions and areas with a high density of Tertiary sills. In these areas sediments are postmature. The potential source rocks are believed to be adequately buried with respect to oil-generation only in the easternmost part of the area, where they apparently passed into the oil-window during Cretaceous time. In this area four play concepts have been suggested, all with Upper Palaeozoic source rocks and respectively Upper Carboniferous, Upper Permian, Middle Jurassic and Upper Jurassic–Lower Cretaceous reservoirs.

C26 and C28-C34 28-norhopanes in sediments and petroleum

Abstract A complete series of 28-norhopanes (C26 and C28-C34) has been detected in oil samples and rock extracts from West Greenland and the North Sea. Only the C28 members of the series (28,30-bisnorhopanes) and the related 25,28,30-trisnorhopanes have been described in the literature. 28,30-Bisnorhopanes are often the only 28-norhopanes in oils and sediments, and their isotopic composition can be different from that of the regular hopanes, suggesting that 28,30-bisnorhopanes have a different origin. In other cases, 28-norhopanes and regular hopanes have a similar distribution of homologues, and there is no isotopic evidence for a different origin of the two series. When the complete series of 28-norhopanes is present, it is usually accompanied by high concentrations of the corresponding demethylated aromatic 8,14-secohopanes. The 28-norhopanes seem to be less resistant to biodegradation than regular hopanes, and there is a preferential demethylation of the low-molecular-weight 28-norhopanes. C25 and C27-C31 25,28-bisnorhopanes have been identified in biodegraded oils. The C28-C34 28-norhopanes are best studied using the m/z 355 mass chromatogram, since this fragment is comparatively intense and the interference from other compounds is usually low. The 17β(H),21α(H)/(17α(H),21β(H)+17β(H),21α(H)) ratios of the C29 and C30 28-norhopanes can be used as maturity parameters. In immature samples, a large proportion of the 28-norhopanes (especially C28 and C30) occurs in the bitumen. However, hydrous pyrolysis experiments have shown that 28-norhopanes are also part of the kerogen.

Denudation and uplift history of the Jameson Land basin, East Greenland—constrained from maturity and apatite fission track data

Abstract The Jameson Land basin in East Greenland comprises a well exposed succession of Upper Paleozoic–Mesozoic sediments. During Middle Devonian–Early Permian rifting, ∼13 km of continental clastics were deposited. In latest Paleozoic to Mesozoic times, ∼4 km of sediments accumulated during regional subsidence. In the Early Paleocene, during North Atlantic break-up, the basin was covered by a thick volcanic pile. Subsequently, uplift and erosion took place over the whole region. The volcanic cover was completely removed from Jameson Land and erosion cut deeply into the underlying sediments. To assess the exploration potential of Jameson Land, a basin modelling study with 21 1D pseudo-wells was carried out based on all seismic and surface data available. In addition to the calculation of hydrocarbon generation in space and time, the basin modelling provided an opportunity to study the magnitude and timing of uplift and erosion. Basin modelling constrained by apatite fission track data has made it possible to determine a consistent uplift and erosion history of the area. Tectonic backstripping based on a simple Airy type isostatic model has been used to separate the tectonic uplift from the actual uplift. The combined basin modelling and backstripping study has led to the following conclusions: (1) the thickness of the Cretaceous succession varied from 1.3 km in the south to 0.3 km in the north; (2) the volcanic rocks formed a wedge with a thickness of >2 km in the south thinning to

Depositional Environment and Organic Geochemistry of the Upper Permian Ravnefjeld Formation Source Rock in East Greenland

The Upper Permian Ravnefjeld Formation in East Greenland is composed of shales that laterally pass into carbonate buildups and platforms of the Wegener Halvo Formation. The Ravnefjeld Formation is subdivided into five units that can be traced throughout the Upper Permian depositional basin. Two of the units are laminated and organic rich, and were deposited under anoxic conditions. They are considered good to excellent source rocks for liquid hydrocarbons with initial average TOC (total organic carbon) values between 4 and 5% and HI (hydrogen index) between 300 and 400. The cumulative source rock thickness is between 15 and 20 m. The source rocks are separated and enclosed by three units of bioturbated siltstone with a TOC of less than 0.5% and an HI of less than 100. The e siltstones were deposited under relatively oxic conditions. The organic geochemistry of the source rocks is typical for marine source rocks with some features normally associated with carbonate/evaporite environments [low Pr/Ph (pristane/phytane), low CPI (carbon preference index), distribution of tricyclic and pentacyclic terpanes]. The establishment of anoxic conditions and subsequent source rock deposition was controlled by eustatic sea level changes. The subenvironment (paleogeographic setting, influx of carbonate material, water depth, salinity) has some influence on a number of bulk parameters [TOC-HI relations, TOC-TS (total sulfur) relations] and, in particular, biomarker parameters such as Pr/Ph and terpane ratios. All the basal shales or shales in the vicinity of carbonate buildups or platforms are characterized by low Pr/Ph, high C23 tricyclic terpanes, and high C35 and C33 hopanes.

Organic geochemistry and source potential of the lacustrine shales of the Upper Triassic - Lower Jurassic Kap Stewart Formation, East Greenland

Abstract The Upper Triassic — Lower Jurassic Kap Stewart Formation (Jameson Land, East Greenland) has been studied by a combination of sedimentological and organic geochemical methods (LECO/Rock Eval, sulphur, gas chromatography) in order to assess the hydrocarbon source potential of the abundant and extensive lacustrine shale intervals present in the formation. The organic matter in the shales is a mixture of algal and higher plant remains (type I and III kerogen). An organic assemblage dominated by algal material, having a rich oil potential, occurs in an interval approximately 10–15 m thick in the uppermost part of the formation. This interval has an organic carbon content up to 10% and Hydrogen Index values up to 700. The interval is consistently traceable along the exposed margins and the central part of the basin. The deposition of the uppermost shale interval coincided with the largest expansion of the lake, during a period with a stratified water column and anoxic bottom-water conditions. Locally the rocks exposed are thermally postmature due to the thermal influence of dolerite sills which intruded the Kap Stewart Formation in Tertiary time. However, the organic-rich shale interval is beyond the influence of the sills and indicates a maturity prior to or in the early stages of oil generation. Calculations of the generative potential of the lacustrine source rocks suggest that significant amounts of petroleum may have been generated in those sediments which have undergone sufficient burial in the southern and central part of the basin. Here, the contemporaneously deposited delta front and barrier island sandstones can thus be considered as potential targets for future hydrocarbon exploration. This type of play may also be of importance in other North Atlantic basins with a similar basin history.

Organic geochemistry of upper palaeozoic lacustrine shales in the East Greenland basin

Abstract The Devonian and Carboniferous-Lower Permian succession in East Greenland includes three geochemically distinct groups of lacustrine shales with a possible petroleum potential: 1. 1. Source rocks with 2–10% TOC, Hydrogen Index betwen 450 and 900, a high content of saturated hydrocarbons, a high content of n -alkanes extending into the waxy range and a distinct odd/even predominance and low to moderate Pr/Ph values occur in the Upper Carboniferous part of the succession. 2. 2. Source rocks with ∼ 10% TOC, Hydrogen Index above 700, a high content of saturated hydrocarbons, a complete dominance of n -alkanes without odd/even predominance, low waxiness and virtual lack of isoprenoids appear to be restricted to the Upper Devonian. 3. 3. Shales with a high content of saturated hydrocarbons, higher contents of branched and cyclic compounds, high Pr/Ph values, low waxiness and max of n -alkanes at C 22 occur in the Middle Devonian.

Exploration significance of lacustrine forced regressions of the Rhaetian-Sinemurian Kap Stewart Formation, Jameson Land, East Greenland

During Rhaetian-Sinemurian time a large wave- and storm-dominated hydrologically closed lake was situated in the Jameson Land basin, East Greenland. The lacustrine succession consists of alternating black unfossiliferous organic-rich mudstones and sheet sandstones. Anoxic conditions dominated at the lake bottom during deposition of the muds, and the water column was probably stratified. Water depth during deposition of the muds exceeded several tens of metres and probably reached a hundred metres. The sandstones were deposited by progradation of wave-dominated deltas in a water depth of less than 15 m. High-resolution sequence stratigraphic interpretation suggests that the mudstones were deposited in periods of rising and high stand of lake level, whereas progradation of the deltaic sheet sandstones took place during forced regressions caused by significant fall. The lake thus underwent a large number of fairly high-amplitude changes in level, probably caused by climatic fluctuations. The high-frequency cycles can be grouped into several low-frequency cycles that show the same number of major fluctuations as published eustatic sea-level curves. This similarity suggests a causal link between eustasy and long-period variations in lake level. Recognition of lowstand shorelines in association with the process of forced regression has led to recognition of a new stratigraphic play type in the Jameson Land basin. Lowstand deltaic sandstone bodies, isolated in organic-rich lacustrine shales with a suitable maturity for hydrocarbon generation, occur in an extensive area in southern and central Jameson Land. In these parts of the basin this play type may be attractive for exploration assuming optimal conditions for hydrocarbon preservation. The Kap Stewart black shale-forced regressive sandstone play type may be applied to similar lacustrine successions elsewhere.

Late Paleozoic plays in East Greenland

A series of Late Paleozoic–Mesozoic basins, which formed as the result of rifting between Greenland and Norway following the Caledonian orogeny, are exposed in East Greenland between 70° and 76°N. The Paleozoic part of the sedimentary basin fill has a cumulative thickness of up to 13 km. The region seems prospective but exploration is still at an early stage without exploration wells. Basic petroleum-related studies of outcrops have been carried out throughout the region, and 1800 km of high-quality multi-fold seismic data have been acquired in Jameson Land between 70° and 72°N. A number of pre-, syn- and post-rift play types are suggested on the basis of inferred source and reservoir rock distribution as well as structural and thermal history. Some of the play concepts have been identified in outcrop, others have been recognized during the seismic interpretation. The principal Upper Paleozoic source rocks include Upper Devonian shales (freshwater), Upper Carboniferous lacustrine shales (freshwater to slightly saline), and Upper Permian marine shales (some carbonate influence). The main reservoir facies are fluvial sandstones in the Upper Devonian to Lower Permian succession and Upper Permian platform and build-up carbonates. Syn-rift Carboniferous plays (mainly structural) and post-rift Upper Permian carbonate plays (essentially stratigraphic) seem most promising. The syn-rift plays have lacustrine shales as source rocks, fluvial Carboniferous to Lower Permian sandstones as reservoirs, and overlying fluvial/lacustrine shales as seal. The post-rift Upper Permian plays have carbonate build-ups and platforms as reservoir targets and the juxtaposed marine shales as source rock and seal.