Gravitational Fingering Due to Density Increase by Mixing at a Vertical Displacing Front in Porous Media
Gravitational Fingering Due to Density Increase by Mixing at a Vertical Displacing Front in Porous Media
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DOI：
10.1021/acs.energyfuels.7b02819
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发表时间：
2018-01-01
期刊：
影响因子：
5.3
通讯作者：
Suekane, Tetsuya
中科院分区：
文献类型：
--
作者：
Wang, Lei;Cai, Shitong;Suekane, Tetsuya
CO2提高采收率在石油生产中已经应用多年。CO2注入引起了越来越多的关注，因为它代表了降低大气中CO2浓度以减少温室气体排放和提高石油采收率的可能解决方案。CO2溶解在油中导致的密度增加产生了不稳定的高密度层，并导致重力指，这可能对混合和流动路径产生重大影响。本文模拟了具有非线性密度特性的可混溶流体对注入过程中的重力指进现象，并利用三维X-射线衍射技术研究了多孔介质中由于混合而导致的密度增加所引起的重力指进现象的特性。X射线计算机断层摄影术在注入过程中，界面附近的混合增强，界面处出现轻微的波动，并生长成高浓度指状物，与相邻指状物相互作用并合并，垂直向下延伸。随着Pedet数的增加，向下运动的指状物与向上运动的周围环境之间的密度差增大，导致指状物的延伸速度和向上流动的速度增加。此外，界面附近的混合变得更强。随着时间的推移，手指的混合长度和相对体积增加。指状物的混合长度的增长与时间成正比，在早期具有较小的斜率，并且在后期切换到较大的斜率增长。随着Pedet数的增加，手指的相对体积迅速增加。在手指，局部碘化钠浓度线性下降和初始界面向下移动的结果，在注射过程中的手指的相互作用增强。随着Peclet数的增加，增强的色散影响了指状物的加宽并降低了指状物的数密度。
CO2-improved oil recovery has been applied in petroleum production for many years. CO2 injection has attracted increasing attention because it represents a possible solution for the reduction of the CO2 concentration in the atmosphere to reduce greenhouse gas emissions and improve oil recovery. The density increase from CO2 dissolution in oil creates an unstable high-density layer and leads to gravitational fingers, which may have a significant effect on the mixing and flow path. In this work, we modeled gravitational fingering during injection by a miscible fluid pair with nonlinear density property and investigated the properties of the fingering resulting from the density increase by mixing in porous media using three-dimensional X-ray computer tomography. During the injection process, the mixing near the interface was enhanced, and slight fluctuations appeared at the interface, which grew into high-concentration fingers that interacted and merged with neighboring fingers and extended vertically downward. With increasing Pedet number, the density difference between the downward-moving fingers and upward-moving surroundings increased, resulting in increases of the finger extension velocity and velocity of the upward flow. Furthermore, the mixing near the interface became stronger. Over time, the mixing length and relative volume of the fingers increased. The growth of the mixing length of the fingers was proportional to time with a smaller slope at early times and switched to a larger slope growth at later times. A rapid increase of the relative volume of fingers was observed with increasing Pedet number. In the fingers, the local NaI concentration decreased linearly and the initial interface traveled downward as a result of the enhanced interaction of the fingers during the injection process. The enhanced dispersion with increasing Peclet number affected the broadening of the fingers and reduced the finger number density.