Complex Micro-Containers (CMC) Transporting Compartmentalized Reaction Mixture for Self-Healing Cement

Abstract

AbstractZonal isolation and cement sheath integrity are vital for a consistent oil and gas production process in an economic and environmentally conscious manner. However, cement is a brittle material that can fail under repeated application of stresses. The objective of this research is developing a novel material Complex micro-containers (CMC) to induce autonomous self-healing properties to the cement using the mechanism of a self-expanding polyurethane foam formation in a crack area.Complex micro-containers (CMC) consist of polyol-loaded polyurea (PUa) micro- and nanocapsules loaded inside the isocyanate-filled core of larger polyurethane (PU) microcapsules. The method of CMC creation includes several steps. During the first step, an oil-in-oil emulsion, composed of organic solvent and polyol-polyamine solution, is created. The second step is made of a polyurea shell formation directly at the surface of the polyol droplets controlled by an addition of isocyanate. As the result of the interfacial polymerization process, micro- and nanocapsules are formed. Then, they are mixed with the isocyanate solution and further emulsified in the water-based media. The droplets of isocyanate with micro- and nanocapsules are encapsulated through polyurethane shell formation by adding polyol.A variety of factors alter the morphology and size of the micro- and nanocapsules including parameters of emulsion's creation, core/shell ratio, and dispersion speed. The optimal content of isocyanate and polyols in cores of polyurea and polyurethane microcapsules, mechanical mixing parameters, and concentration of emulsifiers in oil-in-oil and oil-in-water emulsions were determined. FTIR-spectroscopy was used to identify the chemical structure and to demonstrate encapsulation of the isocyanate core and the polyurethane shell and the polyol core and polyurea shells. TGA-analysis, optical microscopy, and scanning electron microscopy methods were used to determine the core content of micro- and nanocapsules and their size. The peeling strength test proved that the release of the microcapsules’ core content occurs by pressure application and the diisocyanate reacts with polyol and water and creates the polyurethane material.The main advantage of CMC is its expandable properties due to the formation of a polyurethane foam in the presence of water that can effectively fill the micro-cracks directly in a place of cement breakage. Integration of developed new material into the cement body will allow for improving a long-term wellbore isolation and mitigating a leakage potential in the cemented annuli.