| Popis: |
Growing worldwide oil demand increased the need of new and efficient oil recovery methods. Gas injection in oil reservoirs is deemed one of the most widely used methods to increase oil recovery. However, the full potential of gas injection is often not realized due to poor vertical and areal sweep efficiency of the gas. Foaming could be a potential solution to mitigate the above challenges in gas-flood processes. This thesis aims to study the behavior of foam in natural sandstone previously subject to water flooding. It provides new insight into processes that could be highly relevant for the application of enhanced oil recovery (EOR) in clastic reservoirs. The main premise of this thesis is that whether stable foam can be generated in the presence of ware-flood residual oil and if so, can such foam increase oil recovery beyond water/gas flooding? These questions were addressed by performing systematic bulk and porous media studies. Firstly, the bulk foaming characteristics of several commercial surfactants were investigated to examine the effects of oil phase on the foamability and foam stability. A foaming agent, the AOS surfactant, which forms a stable foam in the presence of alkane-type oils, was thus identified. Secondly, the flow of that surfactant foam in natural sandstone was studied in the absence of oil. Effects of surfactant concentration and injection velocity on the foam mobility and foam propagation were examined in detail. Mechanisms involved in the foam mobility reduction were also explored. Knowledge obtained from the above part formed a basis for further study of the behavior of foam in porous media in the presence of oil. Thirdly, foam flow in water-flooded sandstone was studied with the aid of X-ray CT scanner, enabling us to provide evidence that stable foam could be obtained in the presence of oil. More significantly, we proved that foam displaced additional oil from water-flooded sandstone. Incremental oil recovery by foam was as much as 23±2% of the oil initially in place after injection of four pore volumes compared to only 5.0±0.5% for gas flooding at the same conditions. These results support the idea that foam is potentially an effective EOR method. |
