Polyacrylic acid for repair of leaky wellbores in CO₂ storage formations and possible applications to sediment deformation studies

A novel application of pH-sensitive polyacrylic acid in sealing cement leakage pathways in wells drilled in geologic CO₂ storage formations is developed. A major concern for geological carbon storage is the ability of the formation to hold CO₂ over the long term. The polymer has low viscosity as long as the pH remains below a threshold value, which is dependent on the concentration of the polymer. The polymer particles swells up to thousand folds of their initial volume and the viscosity increases several order of magnitude in response to change in the ambient pH. The optimum polymer concentration, salinity and pH are determined for injection into a well in order to enter the smallest of fractures and leakage pathways, while still providing a strong seal against the leakage of brine containing dissolved CO₂. The resistance of the polymeric gel is improved against salts under a variety of conditions relevant to field application by incorporating of chelating agents and modifying the injection process. Rheological measurements are conducted on pH-sensitive polyacrylic acid at various concentrations and pH values to obtain a simple mathematical model of the rheology of the polymer. Flow curves are obtained at various concentrations and pH values, rescale shear stress and shear rate values, so that all the flow curves collapse on a single master curve. The feasibility of stopping leaks with gel by injecting the polymeric gel into the CO₂ formation is successfully tested. Second, the impact of microstructural controls on the material's rheology is investigated. The polymer dispersion has particles with diameter of several microns, which is shown in our field test to penetrate easily through fractures. SEM imaging techniques are applied to Carbopol suspensions under varying pH and concentrations to establish the correlation between microstructure and the rheology of the gel and the mechanism behind the yield stress build-up. This correlation showed as the free spaces between cross-linked network decreases, the yield stress increases. The third objective of this research is to find the key factors affecting fluid escape pipes in sediments and fractures in rocks in order to explore their features and origins, so that they can be more easily controlled. In order to get an overview of the shape and growth of crack propagation over time, experiments using 2D Hele-Shaw cell are conducted. The impact of the concentration of the polymer, pH of polymer dispersion and the buoyancy on crack propagation in polymer gel is investigated. The polymer gels with higher concentrations showed more localized channeling pattern with less branching. For 3.0 wt. % concentration of polymer gel, the breakthrough pattern showed less branching, more localized and thicker fingers with decrease in yield stress.Chemical Engineerin