CO2 permeability of Indian bituminous coals: Implications for carbon sequestration
CO2 permeability of Indian bituminous coals: Implications for carbon sequestration
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DOI：
10.1016/j.coal.2012.11.003
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发表时间：
2013
影响因子：
5.6
通讯作者：
V. Vishal;P. Ranjith;T. Singh
中科院分区：
文献类型：
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作者：
V. Vishal;P. Ranjith;T. Singh
煤的渗透率是评价煤层作为甲烷储集层或二氧化碳汇性能的最关键参数之一。煤的储层特性为产气动态的长期规划和储层排水提出了许多挑战。此外，煤在盆地间、煤层间和同一煤层部分内的非均质性使这一过程更加复杂。为了最好地估计其行为，需要对储层进行特定的了解。煤基质的收缩/膨胀、气体流动与滑移、地质力学变化、各向异性和有效应力等因素控制着煤中气体的流动行为。近几十年来，这些方面的研究在世界各地不同的盆地得到了发展。然而，目前还没有关于印度冈瓦纳煤的膨胀诱导渗透特性和有效应力作用的研究。考虑到印度煤具有较高的co2储气潜力，在三轴条件下对印度Jharia盆地Barakar组烟煤进行气相co2测试。本文给出了有效应力变化的结果，即围应力和孔隙压力，并考虑了煤随时间膨胀对气态CO2流动模式的影响。在新开发的三轴单元中，针对不同的目标煤层深度，煤受到不同的围应力。对于每个约束，在不同的注射压力下注入二氧化碳。为了最大限度地减少温度对气相特性的影响，在使用排水测试方法时，将下游压力保持在26°C恒定。结果表明：在低约束条件下，随着注气压力的增加，煤的渗透性开始下降，随后趋于稳定；然而，在高围压下，渗透率随着注入压力的增加而增加。煤中的膨胀有助于降低渗透性。在初始约束阶段，随着注气压力的变化，煤的体积膨胀降低了渗透率。随着围压的增大，煤的渗透率降低1 ~ 2个数量级。最后，以印度煤为例，建立了有效应力和溶胀对煤渗透率影响的经验关系式。在较低的有效应力下，对数递减模型更适合，而在有效应力bb0 12MPa时，指数递减关系更适合数据。
The permeability of coal is one of the most critical parameters in estimating the performance of coal seams as methane reservoirs or carbon dioxide sinks. The reservoir behaviour of coal offers many challenges for the long-term planning of gas production performance and the drainage of water from reservoirs. Moreover, heterogeneity in coal from basin to basin, from seam to seam and within parts of the same seam makes the process more complex. Reservoir-specific understanding is needed for the best possible estimation of its behaviour. Factors such as shrinkage/swelling of coal matrix, gas flow and slippage, geomechanical changes, cleat anisotropy and effective stresses control the flow behaviour of gases in coal. Studies of these aspects have gathered momentum in recent decades for different basins across the world. However, no research is available on swelling-induced permeability characteristics or the role of effective stresses for Gondwana coals in India. Considering the fairly high CO2storage potential of Indian coals, bituminous coals of the Barakar Formation in Jharia basin, India were tested using gas phase CO2under triaxial conditions. This paper presents the results of changing effective stresses, in terms of confining stresses and pore pressure, incorporating the role of coal swelling with time on the flow pattern of gaseous CO2. Corresponding to different depths of target coal seams, coal was subjected to different confining stresses in a newly-developed triaxial cell. For each confinement, CO2was injected at different injection pressures. To minimize the effects of temperature on the characteristics of the gas phase, it was kept constant at 26°C throughout, while use of the drained method of testing maintained the downstream pressure equal to one atmosphere. The results showed that at low confinement, increase in gas injection pressures leads to an initial decrease in permeability of coal, which then becomes almost constant. However, at higher confinements, the permeability increases with increasing injection pressure. Swelling in coal contributes to reduction of permeability. The volumetric expansion in coal reduces the permeability with changing gas injection pressure during the initial confinement. As the confining pressure is increased, coal permeability reduces by one to two orders of magnitude. Finally, an empirical relation accounting for the role of effective stresses and swelling on coal permeability is proposed for Indian coals. At lower effective stresses, the logarithmic decline model is better suited, while the exponential decline relationship fits the data better at effective stresses >12MPa.