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Abstract: This study investigates the effect of water pressure on hydrocarbon generation and maturation of coals. Using a 25ml Hastalloy pressure vessel, two high-volatile coals (Longannet, UK 0.75% Ro, and perhydrous Svalbard (Spitsbergen), Norway 0.68% Ro) were pyrolysed under non-hydrous, hydrous at 175bar pressure, and high water pressure hydrous (500bar and 900bar) conditions at 350°C for 24h. The bitumen yield obtained during pyrolysis, together with the Rock–Eval S 2, hydrogen index (HI) and vitrinite reflectance (VR) results from the pyrolysed coal residues indicated that water under relatively low pressure (175bar) hydrous conditions promoted hydrocarbon generation and coal maturation in relation to non-hydrous conditions, consistent with previous work. However, under high water pressure (500 and 900bar) conditions, a combination of the hydrocarbon gas (C1–C4) and bitumen yields, Rock–Eval S 2, HI, VR and solid state 13C NMR results demonstrated that the changes in reaction pathways occurring with increasing pressure resulted in both hydrocarbon generation and maturation being retarded. The observed effect of pressure implies that for Type III source rocks, hydrocarbon generation will be retarded in high pressure geological basins, with gas yields being proportionally reduced more than bitumen yields. Source rock maturation (or coalification) is also retarded, with the decreases in vitrinite reflectance and carbon aromaticity being relatively small but significant in terms of explaining retardation in geological basins. [Copyright &y& Elsevier]

Central Tertiary Basin (CTB) coals from a variety of palaeogeographic conditions within the Longyear and Verkhnij seams, were sampled to assess the relationship between the petroleum present, the remaining generation potential and coal geochemistry in order to improve the spatial predictability of petroleum resources within the basin. Vitrinite reflectance (VR) values from the CTB coals have been shown to be suppressed (Marshall et al., 2015b). This study attempts to quantify and correct for this suppression effect by applying the Lo (1993) method (LoVR), which uses Hydrogen Index (HI) values to modify VR data, and the coal Rank( S r ) scale of Suggate (2000, 2002), a technique not affected by suppression. In addition, the oil generation and expulsion thresholds for the CTB coals were investigated, with discussions on oil potential versus marine influence upon the mires in which the coals formed. A pseudo-van Krevelen diagram shows that the majority of the coals plot on the Type II kerogen line, while the remainder plot between the Types II and III kerogen lines, with HI between 151 and 410 mg HC/g TOC; however, maceral analysis shows that Type III kerogen predominates. This is attributed to the presence of abundant fluorescing (oil-prone) vitrinites. The LoVR, T max and Rank( S r ) parameters all show that maturity increases from basin margins towards basin centre (i.e. from Bassen to Lunckefjellet, to Breinosa and Colesdalen) and indicate that all the coals are within the oil generation window. The marginal samples at Bassen are within the early mature stage of the oil window (i.e. ~ 0.7% R O ); meaning the threshold for oil generation in the basin could not be clearly defined. However, the observed maturation trend somewhat parallels the maturation pathway of the New Zealand Coal Band (NZ Coal Band) and the “envelope” of the Sykes and Snowdon (2002) NZ coal data-set; therefore, it is considered that the oil generation threshold for the CTB coals is likely at Rank( S r ) ~ 9–10, T max ~ 420–430 °C in line with the observed rise in Bitumen Index (BI). Some of the Lunckefjellet coals and all the Breinosa and Colesdalen coals have either reached or progressed beyond the threshold for oil expulsion as indicated by the peak in HI at Rank( S r ) ~ 11–12, LoVR ~ 0.75–0.85% R O , T max ~ 430–440 °C. The peak in BI at Rank( S r ) ~ 12.5–13.5 suggests that some of the Lunckefjellet and Breinosa coals, and all the Colesdalen coals have reached the “effective oil window”. Total sulphur (S T ) contents range between 0.46 and 12.05% indicating non-marine to strong marine influence upon precursor peats, with S T contents of the Longyear seam appearing to record instances of coastal retreat associated with base level rise. Marine deposition seems to significantly control the distribution of oil-prone coals within seams and across the CTB. The levels of marine influence (as indicated by S T content) show clear positive relationships between BI and HI within the Bassen samples because they have not started expelling oil. Conversely, the levels of marine influence show clear negative relationships with BI and HI within the Colesdalen samples because they have commenced oil expulsion, and probably reached the “effective oil window”. The more marine influenced coals appear to have commenced petroleum generation relatively earlier, which is a plausible explanation why the coals from the Lunckefjellet locality appear to be at different stages within the oil window. [ABSTRACT FROM AUTHOR]

Abundant oil prone coal (Type III kerogen) deposits are preserved within the high latitude, middle Palaeocene, Todalen member of the Central Tertiary Basin, Spitsbergen Island, Norwegian Arctic. The coals (Svea, Longyear, Svarteper and Askeladden seams) have been subjected to only minor previous geochemical characterisation. Focussing upon the Longyear seam, this paper characterises the present, prospective and economic oil potential of the Svalbard coals. Organic biomarker parameters, Fe–S chemistry and coal maceral analysis are then applied to understand the provenance and environmental origins of this unusual source rock. The upper Todalen Mbr. coals (Longyear, Svarteper and Askeladden seams) have significantly more oil potential than the Lower Svea seams with estimated retortion yields of 170–190 kg/tonne vs. 24 kg/tonne respectively. The Longyear seam exhibits relatively high HI values (ca. 300–400 mg/g TOC) consistent with a hydrogen rich mixed Type II/III kerogen source. Greatest oil potential is shown to be favoured by formation within a fen environment, with high bacterial degradation (> 100 μg/g TOC hopanes), marine influence (> 0.5 wt.% sulfur, Fe/S < 0.9) and the unique temperate high latitude Palaeocene climate of Svalbard leading to preservation of hydrogen rich organic matter via organo-sulfur bond formation. [ABSTRACT FROM AUTHOR]

The Central Tertiary Basin is an uplifted part of the North Barents Shelf and should be an ideal location to understand the thermal history, maximum burial depth and overburden thickness in this petroleum-rich area. Efforts to quantify the thermal history of the region have been hampered by reports of hyper-thermal conditions, maturity gaps and maturity inversions in the Tertiary vitrinite reflectance (R o ) record. This has been attributed to thermal insulation effects, vitrinite reflectance due to bitumen impregnation and later Tertiary volcanism. Through the use of R o , organic maturity parameters, 13 C NMR and Rock–Eval pyrolysis, this study aims to explain the unusual maturity effects observed and the implications for burial models. Within single seams, R o % ranges from 0.5 to 0.78 with increasingly bimodal distribution up-seam. Analysis of coal aromaticity and the results of Rock–Eval analysis confirm that maturity gaps and inversions only occur where the vitrinite reflectance has been suppressed by high bitumen content (300–400 mg/g coal). Samples with the lowest hydrogen index values (< 250 mg HC / TOC) provide the most accurate estimates of the vitrinite reflectance. Results indicate maximum burial temperatures of 120 °C in the basin centre and 100 °C at the basin margins with a hyper-thermal gradient of approximately 50 °C/km. This gradient implies a total overburden of 2 km of which 1 km has been lost. Maximum burial depth and total erosional sediment load to the Barents Shelf are therefore at the lower end of current estimates. [ABSTRACT FROM AUTHOR]