Semester of Graduation
Master of Science (MS)
Drilling through low pressure formations, either offshore or through depleted formations, requires the use of low density fluids to prevent lost circulation ensuring proper placement of cement for proper zonal isolation and structural integrity. Achieving these densities in cements can be done through foaming the cement, increasing water content, or using silica-based microspheres. Water extended cements are useful at densities down to 13 ppg below which only foaming and silica-based microspheres can be used. Each of these methods coming with individual limitations, with foamed cements being sensitive to high pressures and silica-based microspheres having chemical instability in the high alkalinity environment of wellbore cements.
This chemical instability creates a hydrophilic gel that is expansive and creates fractures in the cement as it expands, which is formally referred to as alkali-silica reactivity (ASR). Prevention of ASR involves the application of additives to the cement that act as a sink for the alkalinity and prevent the expansion of ASR. The sink works by having highly reactive silica in the cement slurry that reacts with the alkalinity during hydration so there is not enough alkalinity in the cement pore fluid to create ASR later in the life of the cement. Lithium nitrate also works as a prevention method by reacting with the silica before the alkalinity, thus creating a new layer of around the silica and preventing reactions with alkalinity.
This study looks at the effects of a high alkalinity cement environment onto the microspheres surface by visualizing the ASR occurring using Scanning Electron Microscopy (SEM). Then cement samples were created to compare the effects of lithium nitrate, fly ash, silica flour, and metakaolin have on cements created with silica-based microspheres. The microstructures of these samples were also imaged using SEM, visualizing that lithium nitrate, fly ash, and metakaolin having the largest impact on preventing reactions with the microspheres. The mechanical properties of these changes were also tested using micro-indentation to give micro-hardness and Young’s modulus. Petrophysical properties of the samples were tested for porosity and permeability. These values provide insight on how each additive’s is effecting the long-term integrity of the cement.
Albers, Dylan, "Prevention of Alkali-Silica Reaction (ASR) in Lightweight Wellbore Cements Containing Silica-Based Microspheres" (2017). LSU Master's Theses. 4354.