Rheology of Supercritical CO2 Foam Stabilized by Nanoparticles

Abstract

Foamed fluids with the gas phase of carbon dioxide (CO 2 ) have been applied as fracturing fluids to develop unconventional resources. This type of fracturing fluids meets the waterless requirements by unconventional reservoirs, which are prone to damage by clay swelling and blocking pore throat in water environment. Conventional CO 2 foams with surfactants have low durability under high temperature and high salinity, which limit their application. Nanoparticles provide a new technique to stabilize CO 2 foams under harsh reservoir conditions. It's essential to determine in-situ rheology of CO 2 foams stabilized by nanoparticles in order to predict proppant transport in reservoir fractures and improve oil production.The shear viscosity and foam texture of non-Newtonian fluids under reservoir conditions are critical to transport proppant and generate effective micro-channels. This study determined the in-situ shear viscosity of supercritical CO 2 foams stabilized by nano-SiO2 in the Flow Loop apparatus with shear rates of 5950~17850 s Ϫ1 at the pressure of 1140Ϯ20 psig and the temperature of 40°C. Supercritical CO 2 with the density of 0.2~0.4 g/ml and the viscosity of 0.02~0.04 cp under typical reservoir conditions were applied to generate foams. The foams were tested with high foam quality up to 80% to minimize the usage of water. The effects of shear rates, salinity, surfactant, and nanoparticle sizes and on the rheology of gas foams with different foam qualities were experimentally investigated. The foam texture and stability were observed through an in-line sapphire tube. Further, proppant transport by CO 2 foams and the placement in fractures were analyzed by considering the rheology of non-Newtonian fluids and the mechanisms of gravity driven settling and hindered settling/slurry flow.The conditions of nanoparticle foaming systems were optimized through orthogonal experimental design. The dense and stable foams were generated and observed under high pressure and elevated temperature conditions. It was observed that CO 2 foams with high quality of 80% demonstrated the highest viscosity and stability under optimal conditions. The foams with nanoparticles demonstrated both shear-thinning and shear-thickening behaviors depending on foam quality and components. The salinity and nanoparticle size affect foam rheology in two ways depending on components, foam quality, and shear rates.While the viscosities of CO 2 foam stabilized by nanoparticles have been widely studied recently, no work has been done to observe the stability and texture of supercritical CO 2 foam after shearing under high pressure and high temperature, not to mention proppant transport by CO 2 foam. This study provided a pioneering insight to the proppant transport by viscous supercritical CO 2 foam stabilized by nanoparticles.

Effects of compositional variations on CO2foam under miscible conditions

“…An important characteristic of foam and emulsion is their non‐Newtonian shear‐thinning behavior, that is, their viscosity decreases by increasing the shear rates. For foam flow in porous media, in the low‐quality regime the apparent viscosity of the foam decreases with increasing shear rates because of the bubble trapping and release and therefore exhibits shear‐thinning behavior . A similar behavior has also been reported for emulsions .…”

Parameter Screening Study for Optimizing the Static Properties of Nanoparticle-Stabilized CO2 Foam Based on Orthogonal Experimental Design

“…Hence, smaller NPs migrate faster into the interface and better improved foam stability is observed than in the larger-sized NPs . The experimental results on the foam height are to some extent consistent with Xiao et al, who found that the foamability could be promoted by either smaller or larger size NPs at different foam qualities.…”

“…Emrani et al found a decrease in the half-life of nanosilica-stabilized CO 2 foam as pressure increased from 300 to 800 psi, while they tested the foam generation capability with shake tests under ambient conditions. Both Xiao et al and Kumar et al carried out the static property studies on NP-stabilized CO 2 foam under atmospheric conditions to help in understanding the supercritical CO 2 foam displacement behaviors in harsh reservoir conditions. It is deduced that the difficulties in evaluating both the static properties of foam height and foam half-life in pressurized containers result in insufficient studies on the effect of pressure on NP-stabilized CO 2 foam .…”

Optimization of Carbon Dioxide Foam Fracturing Technology for Shale Gas Reservoir

“…Mazza [23] believes that liquid CO 2 is most suitable for low-pressure and dry gas reservoir stimulation, because the previous fracturing fluid will destroy gas permeability. Xiao et al [24] and Wang et al [25] believe that foam has been widely used in unconventional reservoir fracturing, and it has more advantages than water-based fracturing fluid, such as less water consumption, rapid flowback, low filtration, and high sand carrying. Due to the significant temperature difference between the reservoir rock and the pumped fracturing fluid, the reservoir rock will be cooled.…”