HIGH-TEMPERATURE EXPOSURE OF OIL WELL CEMENTS

摘要

Cement systems of typical compositions for elevated temperature applications were exposed to temperatures ranging from 350 to 650°F for timeframes ranging from two weeks to six months. The cements were examined at predefined intervals to track changes in phase development and properties. Crystalline silica in the form of quartz was added to the cements in varying concentrations to avoid a detrimental phase transformation linked to a phenomenon called strength retrogression. X-ray diffraction (XRD) with Rietveld refinement was used to track the crystalline phase development in the cement over time. The quartz concentration at each timeframe was found to be linked to the initial quartz concentration used, as well as the timeframe and temperature of exposure. Results indicate that some cement systems with concentrations of silica greater than 35 to 40% by weight of cement might not be adequate to offset strength retrogression at all temperatures and timeframes.