含喉部裂隙介质CO_2反应迁移的格子Boltzmann模拟研究

Lattice Boltzmann simulation of CO_2 reactive transport in throat fractured media

CO_2地质封存是目前最经济、最可靠的CO_2减排技术之一,对CO_2反应迁移规律的研究具有重要的理论价值。采用Dardis多孔介质模型与已有的CO_2反应迁移模型耦合,对含喉部裂隙的复杂介质中反应迁移规律进行模拟研究。速度场的模拟结果表明,裂隙内的速度明显高于基质速度,在喉部中心线位置处速度达到最大值。溶解反应主要集中于入口段及裂隙的上、下边缘附近;受喉部的影响,喉部下游的裂隙边缘几乎不发生溶解反应。反应物H^+在裂隙及喉部中的浓度明显高于在基质中的浓度;而生成物Ca^(2+)的高浓度区则出现在下游基质区中。针对不同喉部位置的情况进行对比,分析其对反应率及组分浓度的影响规律。最后对含突扩孔的裂隙介质进行了模拟,发现其提高了裂隙内的速度及组分迁移,这与喉部裂隙介质内的规律正好相反。上述结果较好地说明了本模型具有模拟研究复杂裂隙介质内的CO_2反应迁移规律的能力。

CO_2 geological storage is one of the most economical and reliable techniques for reducing CO_2 emission,and the understanding of CO_2 reactive transport in reservoirs is critical for that.Dardis＇ s porous model,coupled with our previous CO_2reactive model,is presented to investigate the reactive transport in throat fractured media.According to the velocity field results,the velocity in fracture is much higher than that in matrix and it reaches the maximum value at centerline in throat.The main dissolution reaction occurs near the inlet region,and along the upper and bottom edges of the fracture.There is nearly no dissolution along the edges after downstream throat,which is mainly affected by the throat.The concentration of H~＋ ion in fracture and throat is higher than that in the matrix;while the higher concentration of Ca^（2＋） ion occurs in the region of downstream matrix.And then,the comparisons among different throat positions are also made to analyze the effects of the throat position on the distribution of dissolution rate and species concentration.Finally,the fractured media with sudden reaming is simulated,and it is found that the velocity and component migration in the fracture are enhanced,which is totally contrary to the case with throat fracture.All the above results show the capability of the present model in simulating CO_2 reactive transport in complex fractured media.