水和超临界二氧化碳两相渗流驱替的岩心及微观模型实验研究

发布时间：2018-02-28 15:10

本文关键词： CO_2地质封存两相渗流溶解相对渗透率岩心与微观模型　出处：《中国地质大学(北京)》2016年博士论文　论文类型：学位论文

【摘要】：CO_2地质封存被认为是目前减轻温室效应的有效途径之一。深部咸水含水层由于其分布广泛,储存空间巨大,被认为是进行CO_2地质封存的理想场所。在进行CO_2咸水含水层封存数值模拟研究时,CO_2和地层水间的溶解被认为是瞬时完成的平衡溶解过程。然而由于岩石多孔介质孔隙、孔隙网络结构的复杂性,以及超临界CO_2(scCO_2)和地层水之间粘度差异,很可能导致scCO_2/水两相无法自由接触,有限的接触面积将极大地限制scCO_2的溶解过程,出现非平衡溶解的现象。值得一提的是,scCO_2的非平衡溶解受到两相渗流的影响,溶解也会对两相渗流具有一定的反馈作用,即发生两种机制的耦合。为了系统全面的研究scCO_2与水间的溶解及渗流场和化学场的耦合过程,分别进行了岩心尺度和孔隙尺度微观模型驱替实验。岩心尺度驱替实验是利用采集自鄂尔多斯盆地的典型低渗透砂岩,在8-10 MPa,40°C条件下完成的。实验过程中首先将岩心饱和水并进行scCO_2驱替实验。在建立残余水饱和度后,进行纯水驱替实验。通过收集和测定岩心出口端流出水中溶解CO_2含量,得到了scCO_2-水在低渗透砂岩岩心中的溶解过程。实验结果表明,水中溶解CO_2含量随着驱替时间变化,并小于实验条件下的CO_2溶解度1-2个数量级,证明了CO_2-水的非平衡溶解过程。通过改变驱替水中溶解CO_2含量背景值和注水速率,对该非平衡溶解过程进行了敏感性分析,建立了CO_2溶解速率随浓度变化的数值模型。为进一步解释岩心尺度观测结果,进行了孔隙尺度微观模型驱替实验。首先在一单晶硅芯片上,利用微观孔隙刻蚀技术,重现真实砂岩岩心的2D孔隙网络结构。在该微观模型中,在9 MPa和40°C条件下,进行了与岩心尺度实验过程相似的水驱替实验。利用微观显微镜成像技术,捕捉到了实时的孔隙尺度scCO_2-水两相渗流与溶解过程。通过图像分析,得到了scCO_2-水非平衡溶解的最直接证据:由于孔隙网络结构的非均一性引起水流的优势流,导致scCO_2-水之间非常有限的接触面积。水中溶解CO_2含量小于实验条件下的CO_2溶解度1-3个数量级。此外,与传统相对渗透率曲线模型和观测结果不同,孔隙尺度实验还观测到了溶解参与下的水相相对渗透率与水相饱和度之间呈现非单调性的变化规律。其原因归结于孔隙网络的双渗透性模式及CO_2的非平衡溶解过程。孔隙尺度实验为岩心尺度驱替实验结果提供了很好的解释与论证,加深了人们对CO_2束缚气封存与溶解封存机制间转换的理解。两相渗流与溶解耦合过程的研究结果也会对其他资源开采(如页岩水力压裂、CO_2提高石油、煤层气采收率、CO_2开发地热等)过程中的多场耦合问题有所启发。
[Abstract]:CO_2 geological storage is considered to be one of the effective ways to reduce Greenhouse Effect. Because of its wide distribution, deep salt water aquifer has huge storage space. It is considered to be an ideal place for CO_2 geological storage. In the numerical simulation of the storage of CO_2 salt water aquifer, the dissolution between CO-2 and formation water is considered to be an instantaneous equilibrium dissolution process. However, due to the pore of porous medium in rock, The complexity of the pore network structure and the viscosity difference between the supercritical COSP _ 2 scCO _ 2) and the formation water are likely to lead to a lack of free contact between the scCO2 / water phases, and the limited contact area will greatly limit the dissolution process of the scCO_2. It is worth mentioning that the non-equilibrium dissolution of scCO2 is affected by the two-phase seepage, and the dissolution will have a certain feedback effect on the two-phase seepage. In order to study the dissolving process between scCO_2 and water and the coupling process of seepage field and chemical field, The core scale displacement experiments were carried out on the micro model of core scale and pore scale respectively. The core scale displacement experiment is based on the typical low permeability sandstone collected from the Ordos Basin. The experiment was carried out under the condition of 8-10 MPA ~ (40 掳C). In the experiment, the saturated core water was first saturated and the scCO_2 displacement experiment was carried out. After the residual water saturation was established, the pure water displacement experiment was carried out. The dissolved CO_2 content in the effluent water from the outlet of the core was collected and measured. The dissolution process of scCO2- water in low permeability sandstone core is obtained. The experimental results show that the dissolved CO_2 content in water varies with the displacement time and is less than 1-2 orders of magnitude of CO_2 solubility under experimental conditions. The non-equilibrium dissolution process of CO2-water was proved. The sensitivity of the disequilibrium dissolution process was analyzed by changing the background value of dissolved CO_2 content and the water injection rate. A numerical model of the variation of CO_2 dissolution rate with concentration was established. In order to further explain the core scale observation results, the pore scale micro model displacement experiment was carried out. Firstly, the micro pore etching technique was used on a single crystal silicon chip. The 2D pore network structure of the true sandstone core is reproduced. In this microscopic model, water displacement experiments similar to the core-scale experimental process are carried out under 9 MPa and 40 掳C conditions. The microscopic imaging technique is used. The real time pore scale scCO2- water two-phase seepage and dissolution process is captured. By image analysis, the most direct evidence of scCO-2- water non-equilibrium dissolution is obtained: the dominant flow caused by the heterogeneity of pore network structure. This leads to a very limited contact area between SCCO2- water. The dissolved CO_2 content in the water is smaller than the CO_2 solubility of 1-3 orders of magnitude under experimental conditions. In addition, it is different from the traditional relative permeability curve model and the observed results. The porosity scale experiment also observed that the relative permeability of water phase and the saturation of water phase show the variation law of non-monotonicity under the participation of dissolution. The reason is attributed to the double permeability model of pore network and the non-equilibrium dissolution of CO_2. The pore scale experiment provides a good explanation and demonstration for the experimental results of core displacement. The results of two-phase percolation and dissolution coupling process will also improve the oil production of other resources (such as shale fracturing and COSP _ 2). The problem of multi-field coupling in the process of coal bed methane recovery is enlightening.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X701;X141

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