Bio-Enhancement of Coal Bed Methane Resources in the Southern Sydney Basin (original) (raw)

The influence of petrological properties and burial history on coal seam methane reservoir characterisation, Sydney Basin, Australia

International Journal of Coal Geology, 2007

Gas content of coals continuously change throughout their burial histories as a result of the changing state of equilibrium of the coal-gas system caused by variations in P-T conditions and coal rank. To fully evaluate the prospectivity of a coalbed methane resource, numerous coal properties, burial history, P-T conditions, hydrology and the likelihood of secondary biogenic gas generation need to be considered with respect to gas sorption capacity, gas contents and permeability. Previous studies have given differing interpretations on relationships between rank and maceral composition with sorption capacity. The maximum gas storing capacities for Sydney Basin coals is inversely related to rank up to medium volatile bituminous, but a coked, contact metamorphosed coal has an elevated capacity. Comparison of sorption capacities of coals having similar ranks and variable maceral group composition, indicate that rank has a dominating effect over any effects of organic matter type. For the Sydney Basin coals, the in-situ gas contents, on average, increase with depth up to about 600 m and with further increases in depth to 900 m, the gas contents tend to plateau or even decrease. Such a trend probably is consistent with the combined effects of pressure and temperature on the gas sorption capacity during the geological history. R-mode cluster analyses of the coal and gas properties yield a positive correlation between gas contents and inertinite abundance. This is related to undersaturation of the vitrinite-rich coals, possibly due to higher permeability and consequent leakage of more gas from vitrinite-rich coals than from inertinite-rich coals. Although a large amount of methane and other hydrocarbon gases would have been generated in the Sydney Basin at maximum burial during the Early Cretaceous, a large proportion of the gas might not have been sorbed within the coal due to limited gas sorption capacities and enhanced diffusivity at high temperatures. Upon uplift, gas that migrated from deeper in the sequence or from shallower biological activity may have been sorbed into the coals. Without secondary gas replenishment however, many of these coals remain significantly undersaturated. The areas that contain considerable amounts of secondary biogenic gas are highly prospective for coalbed methane production partly because of the higher gas contents, but also because of the higher permeability, which is required for access of the microbes and nutrients in meteoric waters. To fully evaluate prospectivity of coalbed methane resources, numerous coal properties, burial history, geologic setting and the likelihood of secondary biogenic gas generation need to be considered with respect to gas sorption capacity, gas contents and permeability.

Significance of microbial activity in Australian coal bed methane reservoirs -- a review

Bulletin of Canadian Petroleum Geology, 2006

Coal bed methane (CBM) is rapidly becoming a significant contributor to energy needs along the eastern seaboard of Australia. The prospective coal seams for methane production in Australia range from Jurassic to Permian in age with ranks varying from sub-bituminous to low volatile bituminous coal. These coals contain mixed gas compositions comprising mainly methane and carbon dioxide with subsidiary amounts of ethane and higher hydrocarbons. Geochemical data for gases and coal indicate extensive microbial activity, especially in coal seams shallower than about 600 m. Microbial activity possibly occurred subsequent to uplift of the eastern Australian basins during the Late Cretaceous and Tertiary. Such microbial activity has contributed to considerable volumes of methane presently stored in the shallow coals of these basins. The two main pathways of biogenic methane generation in coal are the carbon dioxide (CO 2-reduction) and acetate dependant (aceticlastic-reaction) methanogenesis by archaea. Carbon and deuterium isotope data indicate that CO 2 reduction is the main pathway of secondary biogenic methane generation in the eastern Australian coal seams. 'Sweet spots' for CBM production are likely to be mainly confined to permeable coal seams where microbial activity has enhanced the methane saturation levels of the coals. In the Sydney Basin, for example, the CBM production rates are up to an order of magnitude higher in areas where coal contains considerable volumes of secondary biogenic gas compared to areas containing only thermogenic gas. In the high producing wells of the Sydney Basin, the isotope fractionation factor for CO 2 and CH 4 is >1.06 which indicates extensive methane generation from CO 2 dependant methanogenesis. RÉSUMÉ Le méthane de charbon (CBM), présent le long de la côte Est de l'Australie, est en train de devenir rapidement un facteur important quant aux besoins d'énergie. Les couches de charbon qui présentent un potentiel de production de méthane en Australie, s'échelonnent de l'âge du Jurassique au Permien, et présentent des gammes de charbons variant du lignite noir

Factors controlling the origin of gas in Australian Bowen Basin coals

Organic Geochemistry, 1998

Open system pyrolysis (heating rate 10°C/rain) of coal maturity (vitrinite reflectance, VR) sequence (0.5%, 0.8% and 1.4% VR) demonstrates that there are two stages of thermogenic methane generation from Bowen Basin coals. The first and major stage shows a steady increase in methane generation maximising at 570°C, corresponding to a VR of 2-2,5%, This is followed by a less intense methane generation which has not as yet maximised by 800°C (equivalent to VR of 5%). Heavier (C2+) hydrocarbons are generated up to 570°C after which only the C1 (CH4, CO and CO2) gases are produced. The main phase of heavy hydrocarbon generation occurs between 420 and 510°C. Over this temperature range, methane generation accounts for only a minor component, whereas the wet gases (C2-C5) are either in equal abundance or are more abundant by a factor of two than the liquid hydrocarbons. The yields of non-hydrocarbon gases CO2 and CO are greater then methane during the early stages of gas generation from an immature coal, subordinate to methane during the main phase of methane generation after which they are again dominant. Compositional data for desorbed and produced coal seam gases from the Bowen show that CO 2 and wet gases are a minor component, This discrepancy between the proportion of wet gas components produced during open system pyrolysis and that observed in naturally matured coals may be the result of preferential migration of wet gas components, by dilution of methane generated during secondary cracking of bitumen, or kinetic effects associated with different activations for production of individual hydrocarbon gases. Extrapolation of results of artificial pyrolysis of the main organic components in coal to geological significant heating rates suggests that isotopicaUy light methane to 313C of-50%0 can be generated. Carbon isotope depletions in 13C are further enhanced, however, as a result of trapping of gases over selected rank levels (instantaneous generation) which is a probable explanation for the range of 313C values we have recorded in methane desorbed from Bowen Basin coals (-5l + 9%0). Pervasive carbonate-rich veins in Bowen Basin coals are the product of magmatism-related hydrothermal activity. Furthermore, the pyrolysis results suggest an additional organic carbon source from CO2 released at any stage during the maturation history could "mix" in varying proportions with CO2 from the other sources. This interpretation is supported by C and O isotopic ratios of carbonates that indicate mixing between magmatic and meteoric fluids. Also, the steep slope of the C and O isotope correlation trend suggests that the carbonates were deposited over a very narrow temperature interval basin-wide, or at relatively high temperatures (i.e., greater than 150"C) where mineral-fluid oxygen isotope fractionations are small. These temperatures are high enough for catagenic production of methane and higher hydrocarbons from the coal and coal-derived bitumen. The results suggests that a combination of thermogenic generation of methane and thermodynamic processes associated with CH4/CO 2 equilibria are the two most important factors that control the primary isotope and molecular composition of coal seam gases in the Bowen Basin. Biological process are regionally subordinate but may be locally significant.

Effects of igneous intrusions on coalbed methane potential, Gunnedah Basin, Australia

International Journal of Coal Geology, 2001

The Gunnedah Basin, NSW, Australia, contains more than 500 Gt of coal, and has been the subject of recent coalbed methane exploration. Large areas of the basin contain igneous intrusions and large areas of coal have been heat-affected as a consequence. A detailed study has been undertaken of coal seams intersected in a cored coalbed methane exploration drillhole in which two sill-form igneous intrusions are present. Comparisons are made between coals that are unaltered and coals that have been heat-affected, using petrographic and chemical data, coal seam gas desorption data, and gas chemical analysis data.

Coal as a source of oil and gas: a case study from the Bass Basin, Australia

APPEA Journal, 2003

Only a few published geochemical studies have demonstrated that coals have sourced significant volumes of oil, while none have clearly implicated coals in the Australian context. As part of a broader collaborative project with Mineral Resources Tasmania on the petroleum prospectivity of the Bass Basin, this geochemical study has yielded strong evidence that Paleocene-Eocene coals have sourced the oil and gas in the Yolla, Pelican and Cormorant accumulations in the Bass Basin. Potential oil-prone source rocks in the Bass Basin have Hydrogen Indices (HIs) greater than 300 mg HC/g TOC. The coals within the Early-Middle Eocene succession commonly have HIs up to 500 mg HC/g TOC, and are associated with disseminated organic matter in claystones that are more gas-prone with HIs generally less than 300 mg HC/g TOC. Maturity of the coals is sufficient for oil and gas generation, with vitrinite reflectance (VR) up to 1.8 % at the base of Pelican-5. Igneous intrusions, mainly within Paleocene, Oligocene and Miocene sediments, produced locally elevated maturity levels with VR up to 5%. The key events in the process of petroleum generation and migration from the effective coaly source rocks in the Bass Basin are: • the onset of oil generation at a VR of 0.65% (e.g. 2,450 m in Pelican-5); • the onset of oil expulsion (primary migration) at a VR of 0.75% (e.g. 2,700-3,200 m in the Bass Basin; 2,850 m in Pelican-5); • the main oil window between VR of 0.75 and 0.95% (e.g. 2,850-3,300 m in Pelican-5); and; • the main gas window at VR >1.2% (e.g. >3,650 m in Pelican-5). Oils in the Bass Basin form a single oil population, although biodegradation of the Cormorant oil has resulted in its statistical placement in a separate oil family from that of the Pelican and Yolla crudes. Oil-to-source correlations show that the Paleocene-Early Eocene coals are effective source rocks in the Bass Basin, in contrast to previous work, which favoured disseminated organic matter in claystone as the sole potential source kerogen. This result represents the first demonstrated case of significant oil from coal in the Australian context. Natural gases at White Ibis-1 and Yolla-2 are associated with the liquid hydrocarbons in their respective fields, although the former gas is generated from a more mature source rock. The application of the methodologies used in this study to other Australian sedimentary basins where commercial oil is thought to be sourced from coaly kerogens (e.g. Bowen, Cooper and Gippsland basins) may further implicate coal as an effective source rock for oil.

Biogenic methane generation in the degradation of eastern Australian Permian coals

Organic Geochemistry, 2001

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 CO 2 which on biogenic reduction to CH 4 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 CO 2 . #

Mapping Methane and Carbon Dioxide Concentrations and δ13C Values in the Atmosphere of Two Australian Coal Seam Gas Fields

Water, Air, & Soil Pollution, 2014

Fugitive greenhouse gas emissions from unconventional gas extraction processes (e.g. shale gas, tight gas and coal bed methane/coal seam gas) are poorly understood due in part to the extensive area over which these emissions may occur. We apply a rapid qualitative approach for source assessment at the scale of a large gas field. A mobile cavity ring down spectrometer (Picarro G2201-i) was used to provide realtime, high-precision methane and carbon dioxide concentration and carbon isotope ratios (δ 13 C), allowing for "on the fly" decision making and therefore an efficient and dynamic surveying approach. The system was used to map the atmosphere of a production coal seam gas (CSG) field (Tara region, Australia), an area containing pre-production "exploration" CSG wells (Casino, Australia), and various other potential CO 2 and CH 4 sources (i.e. wetlands, sewage treatment plants, landfills, urban areas and bushfires). Results showed a widespread enrichment of both CH 4 (up to 6.89 ppm) and CO 2 (up to 541 ppm) within the production gas field, compared to outside. The CH 4 and CO 2 δ 13 C source values showed distinct differences within and outside the production field, indicating a CH 4 source within the production field that has a δ 13 C signature comparable to the regional CSG. While this study demonstrates how the method can be used to qualitatively assess the location and source of emissions, integration with atmospheric models may allow for quantitative assessment of emissions. The distinct patterns observed within the CSG field demonstrates the need to fully quantify the atmospheric flux of natural and anthropogenic, point and diffuse sources of greenhouse gases from individual Australian gas fields before and after production commences.

Stable isotopic and molecular composition of desorbed coal seam gases from the Walloon Subgroup, eastern Surat Basin, Australia

2014

This study used compositional and stable isotopic analysis to test hypotheses on the distribution and origins of Walloon Subgroup coal seam gas (CSG) in the eastern Surat Basin, Queensland, Australia. The Middle Jurassic Walloon Subgroup play differs from many other low-rank CSG plays-particularly in methane carbon isotopic signature, i.e., the CSG is not as 'microbial' as could be expected. The carbon isotope compositions of desorbed methane from three cored appraisal wells fall within the generally accepted range for thermogenic or mixed gas (δ 13 C −58.5‰ to −45.3‰). The δ 13 C-CH 4 values from stratigraphically placed coal core samples increased (became more 'thermogenic') from the top of the upper (Juandah) coal measures to the base of the Tangalooma Sandstone. Below the Tangalooma Sandstone, in the lower (Taroom) coal measures, the δ 13 C-CH 4 values decreased with increasing depth. These positively parabolic δ 13 C profiles tracked total measured gas content in two out of the three wells studied. The third well displayed lower variance of δ 13 C-CH 4 and gas content increased uniformly with depth. A genetic classification based on methane stable carbon isotopes alone might interpret this pattern as a transition from microbially-to thermogenically-sourced methane in the central coal seams. However, a δ 13 C-CO 2 profile for one well tracks total gas content and δ 13 C-CH 4 , and exhibits an inverse relationship with δD-CH 4. These results, together with the mostly dry nature of the gas samples [(C 1 /(C 2 + C 3)) ratios up to~10,000] and relatively uniform δD-CH 4 values (δD − 238‰ to −202‰), suggest that microbial CO 2 reduction is the primary source of Walloon Subgroup methane. As such, stratigraphic variations in gas content mainly reflect the extent of microbial methanogenesis. We suggest that peak microbial utilisation of H 2-CO 2 occurred at the Tangalooma Sandstone level, enriching the residual CO 2 pool and derived methane in 13 C. Carbon [Δ 13 C(CO 2-CH 4)] and deuterium isotopic differences [ΔD(H 2 O-CH 4)], and cross-plots of δD-H 2 O and δ 18 O-H 2 O are also consistent with kinetic isotope fractionation during microbial-mediated carbonate reduction. The results are relevant for applying microbially enhanced coal bed methane (MECoM) in the Surat Basin.

Coal type, microstructure and gas flow behaviour of Bowen Basin coals

Methane production from coal serms rather than from porous sandstone reser,rcirs is now recognised as a rm.luable and recowrable energy source in Australia. The Permo-Triassic Bowen Basin, Queensland, possesses well defined coal seams, wbich contain major methane resources. Howerrer, commercial g:rs production to date has been ha-urpered by the low permeabilities of coal seams.