Adsorption-induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams
Adsorption-induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams
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DOI：
10.1029/2004jb003482
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发表时间：
2007-10-09
影响因子：
3.9
通讯作者：
Chikatamarla, Laxmi
中科院分区：
文献类型：
--
作者：
Cui, Xiaojun;Bustin, R. Marc;Chikatamarla, Laxmi
[1]将CO2和H2S封存到深部不可开采煤层中是一种有吸引力的选择，可以减少它们向大气中的排放，同时取代预吸附的CH 4，这是一种清洁能源。高煤层渗透性是有效和实用的CO2和H2S封存和CH 4回收所必需的。然而，吸附到煤中的CO2和H2S引起煤基质的强烈膨胀（体积应变），从而通过使裂缝孔径变窄甚至闭合而显著降低煤的渗透率。我们对加拿大西部三种煤的实验数据表明，吸附引起的体积应变近似线性正比于吸附气体的体积，对于相同的气体，不同的煤有非常相似的体积应变系数。利用我们开发的应力和渗透率模型分析了吸附膨胀对井筒周围应力和渗透率的影响。我们的模型结果表明，吸附引起的体积应变有显着的控制应力和渗透性的生产和封存煤层，从而潜在的酸性气体封存。煤层在产甲烷井眼周围的渗透率可能会增加10倍以上，这是由于甲烷解吸引起的煤收缩伴随着储层压力降低而导致的有效应力降低。另一方面，注入H2S和CO2导致强烈的吸附诱导膨胀和有效应力的显着增加，这反过来又导致煤层渗透率降低了几个数量级。注入N-2和CO2的混合物，如在烟道气中发现的，导致较弱的溶胀，其量随气体组成而变化，并为大多数煤提供了封存CO2和二次回收CH 4的最大机会。由于煤在H2S存在下的显著膨胀，即使少量的H2S也会导致渗透率的显著降低，因此在深部煤中封存H2S可能是不切实际的。此外，由酸性气体的吸附产生的高应力将潜在地导致煤屈服、破裂或滑动，并产生细颗粒，其进一步影响渗透性，并因此影响甲烷产生和酸性气体封存。
[1] Sequestration of CO2 and H2S into deep unminable coal seams is an attractive option to reduce their emission into atmosphere and at the same time displace preadsorbed CH4 which is a clean energy resource. High coal seam permeability is required for efficient and practical sequestration of CO2 and H2S and recovery of CH4. However, adsorption of CO2 and H2S into coals induces strong swelling of the coal matrix (volumetric strain) and thus reduces significantly coal permeability by narrowing and even closing fracture apertures. Our experimental data on three western Canadian coals show that the adsorption-induced volumetric strain is approximately linearly proportional to the volume of adsorbed gas, and for the same gas, different coals have very similar volumetric strain coefficient. Impacts of adsorption-induced swelling on stress and permeability around wellbores were analytically investigated using our developed stress and permeability models. Our model results indicate that adsorption-induced volumetric strain has significant controls on stress and permeability of producing and sequestrating coal seams and consequently the potential of acid gas sequestration. Coal seams may undergo > 10 times enhancement of permeability around CH4-producing wellbores due to a reduction in effective stress as a result of coal shrinking caused by methane desorption accompanying a reduction in reservoir pressure. Injection of H2S and CO2 on the other hand results in strong sorption-induced swelling and a marked increase in effective stress which in turn leads to a reduction of coal seam permeability of up to several orders of magnitude. Injection of mixtures of N-2 and CO2 such as found in flue gas results in weaker swelling, the amount of which varies with gas composition, and provides the greatest opportunity of sequestering CO2 and secondary recovery of CH4 for most coals. Because of the marked swelling of coal in the presence of H2S, even minor amounts of H2S result in a marked reduction in permeability, and hence sequestration of H2S in deep coals will be likely impractical. Furthermore, high stresses resulting from sorption of acid gases will potentially cause the coal to yield, fracture or slip, and produce fine particles, which further affect permeability and thus methane production and acid gas sequestration.