CO2在深部咸水层中的埋存机制研究进展

 目前,在深部咸水层中实施CO₂地质埋存的减排处理,是减缓温室效应最有效的现实选择.CO₂在咸水层中的埋存机制主要包括构造圈闭埋存、残余气埋存、溶解埋存和矿物埋存4种基本方式.构造圈闭埋存是CO₂向上运动到致密隔层受到遮挡后,在地质体中聚集,形成CO₂气相埋存,构造圈闭埋存埋存包括闭合构造和开放构造,闭合构造的优势是可以有效限制储层中自由CO₂的横向和纵向运移,缺点是气水接触面被限制在一个十分小的接触区域中,从而限制了CO₂溶解,开放构造的优势是CO₂和周围地层水大面积接触,有利于CO₂溶解,缺点是需要对一个很大的区域进行精细表征以确定可能的气体泄漏路径并进行区域监控;残余气埋存是由于驱替和吸吮相渗滞后,部分CO₂以残余气形式被埋存起来;溶解埋存是CO₂溶解在水中,与水中的钙、镁、铁等离子发生反应生成碳酸盐矿物,实现CO₂圈闭埋存;矿物埋存是CO₂与储层岩石发生缓慢的化学反应形成碳酸盐矿物或HCO₃^-,实现CO₂埋存.各种埋存方式随埋存时间不同,发挥的作用不同,埋存安全性级别也各不相同.本文对咸水层CO₂埋存机制进行深入研究,以期指导中国咸水层CO₂埋存工程顺利进行.

CO2 Storage Mechanism in Deep Saline Aquifers

The storage of CO₂ into saline aquifers is the best way to mitigate the green house effect. The storage of CO₂ in deep saline aquifers mainly concerns the water storage, the residual gas storage, the dissolved storage and the mineral storage. The hydrodynamic trap is formed by the upward movement of CO₂ to dense layers, which is trapped and aggregated in the geological body. The hydrodynamic traps include the open and the enclosed traps. The advantage of an enclosed trap is that the migration of CO₂ is confined both horizontally and vertically, and the disadvantage is that the dissolution is restricted by the limited gas-water contact area. The advantage of an open trap is the significant quantity of CO₂ dissolution caused by a large area of gas-water contact, and the disadvantage is the need of fine characterization of a large area to determine the possible gas leakage path and the need of regional monitoring. Due to the lag of the displacement and sucking phase permeability, a part of CO₂ is stored as the residual gas to form the residual gas trap. The CO₂ dissolved in water reacts with the ions of calcium, magnesium and iron, to generate carbonate minerals, and to form the dissolved storage. The mineral storage formed by the slow chemical reactions between CO₂ and reservoirs rocks would generate carbonate minerals or bicarbonate ions. With different storage durations, the various storage methods play different roles, and the storage security levels also vary. The study of the storage mechanism of CO₂ in saline aquifers will provide some guidance for China's CO₂ sequestration project.