Predicting generation and expulsion of paraffinic oil from vitrinite-rich coals

Abstract

International audienceRock—Eval HI values for coals vary with rank and do not give a direct measurement of oil potential. However, oils from coals are characteristically paraffinic and can be considered to derive from a polymethylene (PM) component, so the PM content should provide an estimate of the paraffinic oil potential. A trend apparently representing lignin evolution has been identified on the Van Krevelen diagram which permits the relative proportions of carbon in lignin and PM to be determined for coals that approximate a mixture of these two components, such as the members of the New Zealand (NZ) Coal Band. On the basis of this compositional model, HI values can be calibrated to provide an alternative estimate of the paraffinic oil potential. A maximum in HI is generally reached in coals near the onset of oil generation, at Rank(S) 12 (R. ca. 0.7%), from which it is suggested that the PM contri¬bution can be obtained using the formula HIpm = 1.15HIma„-172 for the suite of NZ coals examined. The onset of oil expulsion can be identified from a variety of geochemical measurements, and occurs in the Rank(S) range ca. 12.0 — 14.5 (Ro ca. 0.7-1.1%) for coals with paraffinic oil potentials exceeding ca. 40 mg HC/g TOC. Data from Taranaki Basin coals correlate well with the theoretical relationship between BI/HIPM and HIpm, using bitumen index (BI = S 1/TOC) values of 10 mg HC/g TOC at the start of oil generation (i.e. bitumen inherited from diagenesis) and 40 mg HC/g TOC at the onset of oil expulsion, suggesting the HIpm model is reasonably accurate for members of the NZ Coal Band. Kinetic modelling of paraffinic oil generation from vitrinite-rich coals may be best approximated by consideration of PM degradation alone

The Rank(Sr) scale: Its basis and its applicability as a maturity index for all coals

“…In a contribution to a comprehensive appraisal of all aspects of the Taranaki Basin , Killops (1996) adopted the New Zealand Coal Band and the Rank(S) classification when interpreting the hydrocarbon geochemistry of Taranaki Basin coals. The New Zealand Coal Band and isorank lines were essential elements in modelling petroleum generation and expulsion in vitriniterich coals (Killops et al 1998).…”

“…Comparison of British Carboniferous bituminous humic and cannel coals indicates that VM tends to increase rather more rapidly with respect to C V than in New Zealand coals. The high-hydrogen components of cannel coals, mainly in liptinite, may differ from the highhydrogen polymethylene component (Killops et al 1998), which could predominate in the range of humic coals.…”

Petrographic and biomarker analysis of xylite-rich coal from the Kolubara and Kostolac lignite basins (Pannonian Basin, Serbia)

“…The observed differences for pale yellow SXC, which were reflected through the highest content of bitumen (Table 1), highest proportion of short-chain n-alkanes and differences in aromatization degree of di-and triterpenoids (Table 2), can be partly related to differences in microbial communities. Prominent C 31 17α(H)21β(H)22(R)-hopane is often reported in low rank coals (Stefanova et al 2005b;Vu et al 2009) and numerous precursors were proposed for this hopanoid biomarker (van Dorselaer et al 1975;Killops et al 1998;Thiel et al 2003;Pancost et al 2007). C 27 17β(H)-and C 29 17β(H)21β(H)-hopanes could originate from heterotrophic bacteria, chemoautotrophic bacteria and methanotrophic bacteria (Neunlist & Rohmer 1985;Duan et al 2004;Bechtel et al 2014;Mitrović et al 2016).…”

The hydrocarbon potential, thermal maturity, sequence stratigraphic setting and depositional palaeoenvironment of carbonaceous shale and lignite successions of Panandhro, northwestern Kutch Basin, Gujarat, Western India

“…The Bitumen Index (BI) [16] and Quality Index (QI) [17] were determined further to evaluate the results ( [19] based on plots of hydrogen index (HI) against Rank (Sr) and T , inferred that as coals mature towards oil expulsion, their apparent potential to generate hydrocarbons (S2) increases. This results an increase in HI from Rank (Sr∼4, T ∼400-420 C, Ro∼0.35-0.4%) to a peak near the onset of oil expulsion at Rank (Sr∼11.12.5, T ∼430-440 C, Ro∼0.65-0.85%).…”