Super-critical carbon dioxide flow behaviour in low rank coal: A meso-scale experimental study
Section snippets
Introduction and background
Of the various CO2 mitigation options, CO2-enhanced coal bed methane (ECBM) recovery is being implemented and tested as a viable option to reduce the amount of CO2 in the earth’s atmosphere, while recovering a valuable energy product: coal bed methane (CH4) [1], [2], [3], [4], [5]. The CO2-ECBM process involves introducing CO2 through an injecting well into deep coal seams, in which CO2 acts as a displacing gas that allows the already adsorbed CH4 in the coal seam to be desorbed, and eventually
Sample preparation
Permeability tests were conducted using natural brown coal samples obtained from the Hazelwood coal mine located at Morwell in South Gippsland, Victoria. The coring, cutting and grinding machines available in the Monash University Deep Earth Energy Research Laboratory (DEERL) were used to produce samples 38 mm in diameter and 76 mm high from large coal blocks. These brown coal samples had around 57% natural moisture content, and to avoid moisture loss from the samples, they were wrapped in
Experimental results and discussion
The following sections discuss (i) the effect of CO2 phase and pressure on permeability in brown coal; (ii) the potential of reversing CO2 adsorption-induced coal matrix alterations using N2 in brown coal; and (iii) the effect of CO2-induced coal matrix alterations in the pore structure of brown coal.
Implications for CO2 sequestration in coal seams
Generally, super-critical CO2 is preferred for CO2-ECBM recovery due to its higher adsorption capacity to the coal matrix [13] and the ability for stable storage of CO2 due its higher densities [59]. However, reduction of CO2 flow ability through the coal matrix during super-critical CO2 sequestration makes the CO2-ECBM process less productive, since the targeted amount of CO2 cannot be stored in the coal mass, leading to unpredictable CH4 recovery. The field-scale CO2-ECBM projects which
Conclusions
The following major conclusions can be drawn from the study:
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Although the reduction of permeability with increasing depth due to associated effective stress variation, is common for any type of coal, the amount of permeability reduction with increasing depth is much higher for low-rank coals compared to high-rank coal, due to their partially mature, soft and highly compressible nature.
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The uniform cellular-like pore structure with relatively large pores in natural brown coal significantly alters
Acknowledgements
The authors acknowledge the use of facilities in the Monash Centre of Electron Microscopy (MCEM) and the funding provided by the Australian Research Council (DE130100124) and the Postgraduate Publication Award (PPA) of Monash University.
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