Ageing of oilfield cement at high humidity: a combined FEG-ESEM and Raman microscopic investigation

The ageing of oil-well cement, Dyckerhoff class G, under saturated water vapour in the presence of carbon dioxide has been studied using the complementary techniques of Raman microscopy and environmental scanning electron microscopy. This combination of techniques has enabled the key components involved in the surface hydration processes to be identified in situ, their time evolution to be monitored directly (without the need for quenching and sample extraction) and this evolution of chemistry/mineralogy to be related to local structural changes. It has also enabled local chemical changes in this highly heterogeneous material to be related to the original cement grain mineralogy. High aspect ratio structural features, rich in aluminium and sulfur, were formed on the grain surface during the ageing process. These were identified as ettringite, which exhibited a diagnostic band at 988 cm exp -1 in the Raman spectrum.