Manzur Ahmed

Biogenic methane generation in the degradation of eastern Australian Permian coals

Abstract Hydrocarbons extracted from one Sydney Basin coal have a distribution of aromatic and aliphatic hydrocarbons consistent with a high degree of biodegradation as previously demonstrated for Bowen Basin coals. On the same basis, hydrocarbons from two other coals from the Sydney Basin are less biodegraded and display an additional minor series of alkylaromatic degradation products. All these degradation reactions generate CO2 which on biogenic reduction to CH4 is reservoired in association with the Permian coal-seams of the Sydney and Bowen Basins, Australia. Variations in access to oxygenated waters, nutrients and micro-organisms are held to be largely responsible for the extent of biodegradation of coal hydrocarbons and for the reduction of CO2.

Effects of biodegradation on Australian Permian coals

Abstract Permian coals from Blackwater, Poitrel and Moura (Bowen Basin, Queensland) have been extracted and characterised by detailed organic geochemical techniques. A variety of source-related aliphatic and aromatic biomarker parameters indicate that these coals from three different locations are similar in terms of organic matter type and palaeoenvironment of deposition. The hydrocarbons extracted from these coals appear to have been generated from predominantly plant-derived organic matter deposited in a fluvio-deltaic environment. Moderately high Pr/Ph ratios, the high proportion of C 29 steranes and very low sterane to hopane ratios are indicative of their largely terrestrial source. Molecular maturity parameters derived from aliphatic and aromatic biomarkers corroborate a measured maturity of 1.0–1.1% R o for these medium volatile bituminous coals. The aliphatic and aromatic hydrocarbon distributions in these coals also allow their differentiation into two groups: biodegraded Moura coals and non-degraded Blackwater and Poitrel coals. Comparison of various compound ratios from the degraded and non-degraded coals indicate the dependence of susceptibility to biodegradation on precise molecular structures. Major aromatic compound classes in coals, generally regarded as being more resistant, may be microbially altered before branched/cyclic alkanes are affected and even before the n -alkanes are completely removed. As reported in crude oils, susceptibility to biodegradation of aromatic hydrocarbons decreases with increasing number of aromatic rings and with increasing number of alkyl substituents. Furthermore, alkylnaphthalenes with 1,6-dimethyl substitution patterns are more susceptible to degradation than other alkylnaphthalene isomers. This study reveals that biodegradation may alter the hydrocarbon composition of coals in a similar way to that observed in crude oils or oil spills, except that aromatic hydrocarbons are altered relatively earlier than aliphatic hydrocarbons in coals compared to oils.

Effect of Nutrient Addition on an Oil Reservoir Microbial Population:Implications for Enhanced Oil Recovery

The increasing demand for petroleum is driving the development of technologies including MEOR (Microbial enhanced oil recovery)—the use of microbes within a reservoir to enhance oil recovery. In this study we initially determined that availablilty of suitable carbon sources was limiting microbial growth and metabolism of an oil reservoir microbial community. Subsequently we identified metabolic processes that are initiated after addition of nutrients that addressed this limitation. Four distinct metabolic pathways were stimulated: (i) fermentation of the added nutrient; (ii) methanogenises of the metabolites of fermentation; (iii) accumulation and decay of biomass; and (iv) oxidation/co-metabolism of petroleum. Biomass, when introduced as a nutrient, led to similar increases in live cell numbers in oil reservoir microcosms as addition of molasses. In addition to acting as a nutrient, disrupted microbial biomass led to formation of oil-water emulsions and significant lowering of the interfacial tension. These results suggest biomass manipulation can play an important role in MEOR.

The distribution and isotopic composition of sulfur in solid bitumens from Papua New Guinea

Abstract Previous geochemical and petrographic studies have only partly revealed the history and origins of solid bitumens from the East Papuan Basin, Papua New Guinea. In particular, the alteration phenomena, the distribution of hydrocarbon components and the increasing yields of pyritic sulfur indicate major effects of biodegradation and reduction of sulfate to sulfide. Sulfur isotope analysis of the three main sulfur fractions (elemental, sulfate and pyritic) showed these to cluster closely around a δ 34 S value near -25‰ An unlimited source of non-marine sulfate of constant isotopic composition is visualized. However, one clear trend in the data is the increase in the 34 S content of pyrite as abundance increases. Such an isotopic relationship might well occur where, on reduction of a pool of sulfate, an early loss or reduction of 32 S species would result in an increase in the 34 S contents of the residual sulfate and product pyrite. Where the oxidation of pyrite to sulfate and sulfur occurs, the relatively greater 34 S content of the elemental sulfur is consistent with previous data.

Reactions accompanying loss of coking ability during the aerial oxidation of coal

Significant loss of coking ability resulted from the aerial oxidation of a coking coal for 49 days at 60 °C and 32 days at 80 °C. No detectable change in the distribution of the extractable aliphatic hydrocarbons and only very minor changes in the distribution of the extractable aromatic hydrocarbons accompanied the oxidation. The virtually unchanged composition of the extractable hydrocarbons during oxidation and/or biodegradation and associated coking suggest these hydrocarbons play a very minor role, if any, in the coking process. A major role for the extractable polar compounds is indicated.