Conventional foams and foamed gels present a variety of relevant properties that make them suitable for use in the oil and gas sector. Some applications include drilling operations, CO2 foam injection, steam foam, foam-assisted water alternate gas (WAG), and gas shut-off techniques to control excessive gas production in oil wells. Foamed gels have also demonstrated great potential as gas and liquid diverting fluids. Furthermore, foam systems can be injected into rock formations as an important means for CO2 and green gases recycling.
In foamed gel applications, an issue of particular interest is understanding the evolution of partially gelled foam bubbles confined in porous media. This is significant because after foamed gel placement in porous media, the pore level configuration of the gelled lamellar structure determines the fluid diverting performance of mature foamed gel barriers.
This paper reports the experimental results of a pore level visualization study conducted to evaluate the evolution of foamed gel after placement in porous media as a function of aging time. In addition, the experiments assisted in the examination of the effect of rock wettability, foamed gel texture, type of gas used for foamed gel formulation, and type of oil that saturates the porous media and how these play on the evolution of the confined foamed gel. Etched-glass micromodels and Helle-Shaw cells were used to visualize the growth of foamed gel bubbles as a function of time. Through image analysis, changes in bubble sizes were quantified and statistically analyzed.
Laboratory evidence indicates that right after immature foamed gel placement in etched-glass micromodels, significant changes in bubble size occur. After the first 20 hours of foamed gel placement inside the pore network model, bubble growth levels off. The lamellar structure in the micromodel reaches a stable configuration, which remains steady for an indefinite period if external instabilities are absent. Quite the opposite was observed when the same foamed gel was placed in a Helle-Shaw cell. In this case, due to the absence of geometric restrictions, homogeneous bubble shapes and rapid bubble growth were observed.
The experimental results demonstrated that porous media wettability, foamed gel texture, the type of gas used for foamed gel production, and the type of oil that saturates the pore models significantly influence the evolution of foamed gel confined in porous media.
In spite of the well known limitations of etched-glass micromodels and Helle-Shaw cells in representing reservoir rocks(1–3), if the visual observations of pore level behaviour are conducted away from the model boundaries, the underlying capillary phenomena do represent those occurring in reservoir media(3). Thus, micromodels facilitate the direct visualization of fluid interfaces movement, making it possible to gather qualitative and semi-quantitative information of foam propagation in porous media, especially on the specific mechanism of foam performance under practical physical situations(1). This explains why the current accepted theories on foam flow have been largely assembled on the basis of pore model observations(4).