Avaliação do avanço da carbonatação em pastas de cimento para Poços CCS: influência da relação água/cimento

Abstract

In order to minimize the amount of greenhouse gas emissions resulting from human activity, Carbon Capture and Storage (CCS) wells have played an important role in reducing the amount of carbon dioxide (CO2) present in the Earth's atmosphere. The cementing of a well intended for CCS technology is a fundamental part of the process, as it must ensure its sealing and stability, preventing leaks of these gases. A cement that is resistant to corrosion caused by CO2 must be used in order to avoid degradation of the cement matrix and that maintains its mechanical properties over time. The objective of this study is to evaluate the progress of cement carbonation in CCS wells and oil wells subject to exposure to CO2, investigating the variation of the water/cement ratio. Three formulations were developed with varying water/cement (w/c) ratios of 0.45, 0.40 and 0.35, composed of water and cement. The specimens initially underwent a 24-h curing process in a thermostatic bath at 60°C. Then, the specimens were immersed in water in an autoclave saturated with CO2. In the autoclave, the specimens were subjected to different time intervals: 14, 28, 56, 84 and 112 days, maintaining a pressure of 2000 psi and a temperature of 60°C. At the end of each time interval, the specimens were characterized using the following techniques: X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and MicroComputed Tomography (Micro-CT). With the result, it was possible to conclude that the formulations with a lower w/c ratio obtained a decrease in the advancement of carbonation. This occurs due to the greater presence of solids in the matrix that causes a decrease in permeability, delaying the advancement of the carbonation process.