| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 105 === Carbon capture and storage (CCS) is considered a promising method of mitigating CO2 emissions into the atmosphere. Geological storage is the most feasible way to permanently store CO2. Saline aquifers are thought to have the greatest storage capacity of all geological storage sites. In the past, a caprock with extremely - low permeability and dense stacking was a typical feature above a sealable geological storage reservoir. A single and thick shale layer was usually considered the best option for caprock. However, there are many types of shale layers that are usually interbedded with permeable layers, such as shaly-sand and silt. This means that these formations are composed of shale and other lithology. This is called a multilayered caprock system in this study.
Except for shale with extremely - low permeability, the permeable layers can provide efficient sealing. Thus, the purpose of this study was to investigate the sealing efficiency of a multilayered caprock system. Because a multilayered caprock system is shale interbedded with permeable layers, the system’s sealing efficiency is calculated as the sum of the sealing efficiency of each layer. In this study, caprock thickness and ScCO2 (supercritical CO2) plume breakthrough time at the caprock are parameters, that affect sealing efficiency. The ScCO2 plume breakthrough time of was calculated using an analytical method derived in this study.
The analytical method used was the frontal advance equation at constant pressure difference derived from Buckley-Leverett theory in this study. Because the ScCO2 plume accumulates beyond the caprock and thus concentrates the pressure, when the ScCO2 plume pressure is larger than the threshold pressure at the caprock formation, the ScCO2 plume will invade the caprock. Therefore, the frontal advance equation at a constant pressure difference was derived and then initially applied to ScCO2 migration at the caprock. In addition, Computer Modelling Group Ltd.’s (CMG) - GEM compositional simulator (CMG-GEM) was used to verify the correction of the analytical solution mentioned above. Two fundamental models (horizontal and vertical) were built to validate the analytical solution for ScCO2-water two-phase flow, respectively. . After the solution had been validated, we proposed a safety index plot derived from the analytical solution. This plot is convenient for determining the sealing efficiency at the caprock. Finally, we applied the analytical solution and safety index plot in a field case to observe and discuss the results.
We found that our analytical solution could be used to calculate the correct ScCO2 plume breakthrough time at the caprock. Moreover, our proposed safety index plot can be considered a graphical solution, the thickness of the caprock and the ScCO2 breakthrough time can be derived from this plot, and then the sealing efficiency at the caprock can be determined.
|
|---|
