Abstract
In this work we present results of long-term aging tests of a novel cement system (cement R) in carbonated brine and effect of reaction with CO2 on the mechanical properties. Aging tests in carbonated brine were performed for one week, four weeks and two months in a pressure cell at 100 bar and 80 °C. For each test, three cores were placed at the bottom of the cell and fully immersed in 3.5 wt% NaCl brine. The cell was then pressurized with CO2 from the top. X-ray computed tomography (CT) was performed prior to and after the aging tests. Macro-porosity was estimated based on selection of appropriate grayscale range. Unconfined compressive strength (UCS) tests were performed on unexposed cores for reference and on the exposed cores after the aging tests. Reaction with the carbonated brine was observed already after one week of aging. The reaction front progressed further into the bulk after four weeks. However, the reaction slowed down after four weeks. There was no significant difference between samples exposed for four weeks and those exposed for two months. Precipitation of minerals on the surface occurred after four weeks, and this process continued after two months. Macro-porosity decreased and net mass increased due to the reaction with the carbonated brine. The UCS tests indicated that one week of aging had little effect on the unconfined compressive strength and Young's modulus. Decrease of UCS and Young's modulus was observed after four weeks and two months of aging. One reason for strength decrease after two months, by about 40 %, was appearance of cracks within the samples that coincided with the reaction front to a great degree. This could have occurred during the depressurization of the cell. The inorganic Cement R works by reacting with water, CO2 and/or brines to expand into available pores and cracks in ordinary well cements. This effect is interesting to study for possible applications in CO2 storage, plug and abandonment and reuse of existing wells.
