Compressibility of nanoparticle stabilized foams for foamed cement applications
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Foamed cement is widely used in the oil and gas industry to provide zonal isolation. Foamed cement provides various advantages vs. pure cement. The primary purpose of foamed cement is to reduce the density of the cement mixture. Consequently, foamed cement can be used in weak formations were reduced exerted hydrostatic pressure is needed to prevent/control cement circulation loss into the formation. However, Due to gas compressibility, foamed cement’s gas injection rate has to be constantly adjusted in order to create a constant density slurry through the height of the cement column. Furthermore, foamed cement’s properties include higher ductility, constant pressure exertion to the formation during cement transition time (gelling) and lower thermal conductivity. The ability of solid silica nanoparticles to generate stable gas/water foams was researched for foamed cement applications. Solid nanoparticles have been shown to permanently stabilize foams by assembling into layers at the gas/water interface. A potential decrease in compressibility of the gas phase by the presence of these armoring bubble layers was investigated. Enhancement of cement’s splitting tensile strength and compressive strength by silica nanoparticles was also investigated. The addition of uncoated silica nanoparticles at various concentrations did not appear to enhance neither cement’s splitting tensile or compressive strength. In most tests with varying silica nanoparticles concentrations, the samples with nanoparticles exhibited a slightly reduced splitting tensile and compressive strength. The exception being the compressive strength of the samples mixed with the highest nanoparticle concentration tested. However, the strength improvement was small vs. its pure cement counterpart. An apparatus to test the compressibility of nanoparticle stabilized foams was built for this research. The functionality of the apparatus was validated using various test fluids. The validation process allowed for the establishment of a compressibility benchmark to compare the compressibility of nanoparticle stabilized foams. A vital conclusion of this process was that generating the particle stabilized foams under pressure would allow for greater discernment between the existence of the armored bubble effect and gas dissolution into the water phase. A type of nanoparticle was identified as having the capacity to generate long term stable foams without the need of surfactant. Partially hydrophobic surface treated silica nanoparticles were utilized to generate gas/water foams under pressure and subsequently their compressibility was measured. The compressibility of these foams did not appear to show the armored bubble effect behaving as an equivalent ideal gas + water mixture. An additional surfactant and particle stabilized foam recipe was tested and displayed the same results. It was concluded that either the particle layers were not fully forming in the foam or in the case they were forming; either foam geometry was not conductive to the distribution of forces or they likely had limited rigidity and buckled when compressed. If the latter was true, the apparatus was not sensible enough to measure the limited rigidity.