Effects of maturity on the pyrolytic fingerprint of coals from North Borneo

Pyrolysis-gas chromatography-mass spectrometry (Py-GC–MS) and thermally assisted hydrolysis and methylation (THM-GC–MS) were applied to 27 coal samples of lignite to high volatile bituminous rank (vitrinite reflectance %Ro = 0.28–0.66) from the Malaysian states of Sabah and Sarawak on Borneo, to investigate rank effects on molecular properties. The molecular fingerprints of these coals appeared to be controlled by diagenetic and, to a smaller extent, early catagenetic transformations (%Ro 0.28–0.50). The molecular assemblages from immature coals consist mainly of lignin-derived material and long-chain (≥ C24) ester-bound polymethylene chains, whereas mature coals are enriched in short (C10–C25) free and/or trapped (isoprenoid) hydrocarbons, alkylated phenols and resinite aromatic derivatives. By comparing a large suite of potential molecular proxies of maturation (indices of pristane formation, resin aromatization, lignin alteration stages, etc.) and other maturity proxies (%Ro, Tmax), rank effects on different coal constituents are illustrated, as well as the suitability of the proxies for specific rank ranges. The results highlight the importance of decarboxylation of long-chain fatty acids (%Ro 0.35–0.40) and the progressive accumulation of resistant aryl-O (probably diaryl ether) bonds at advanced stages of maturity. The coals from Pinangah in Sabah were more mature than those from Sarawak (Mukah and Balingian coalfields), whereas the molecular signature of other coals from northeastern Sabah (Sandakan area) and southeastern Sabah (Silimpopon and Maliau areas) varied across the rank range studied.This study was partially financed through grants RP002C-13AFR and FP042-2013A. We are grateful to Klaas Nierop (Utrecht University) for valuable discussions on FAMEs patterns and to the anonymous reviewers for their insightful comments.Peer Reviewe

Petrological and Organic Geochemical Characteristics of Oil Sands from the Middle Jurassic Yan'an Formation in the Southern Ordos Basin, China

An integrated petrological and geochemical analysis of surface and drilled oil sands was conducted to assess the organic matter origin/type, thermal maturity and paleoenvironment. Petrographic analysis of the oil sand used to establish the relationships between porosity and permeability with bulk density, RQI, NPI and FZI. The strong correlation between reservoir quality index (RQI) and permeability (R2 = 0.98) reveal that porosity has a good correlation to RQI. The biomarker signatures of the analyzed oil reveal predominance of subaquatic-derived source input with mainly land plant materials. This was indicated based on the average concentration of αααC27:C28:C29 sterane 20R of about 38%, 22% and 40% respectively. This interpretation is also supported by high values of tricyclic terpane/αβC30 hopane and regular sterane/αβC30 hopane. An anoxic condition of deposition within a lacustrine paleoenvironment that attributed to the enhancement of the preservation of the organic matters in the area were indicated based on the low Pr/Ph ratios (average 0.74), low values of αβC31-22R-hopane/αβC30 hopane ratios and high C26/C25 tricyclic terpane ratios as well as the presence of gammacerane and a low water salinity. Biomarker maturity parameters show that the extracted oil sand has entered the early oil window stage. Editorial material and organization © 2019 Geological Society of China. Copyright of individual abstracts remains with the authors