Bai Mingxing

Low Cycle Fatigue of Class G Well Cement

This paper aims to investigate the low cycle fatigue behavior of Class G well cements. While fatigue is well described for metals, wellbore cement fatigue is a rather unknown field. As well cements can be exposed to cyclic loadings situations like in enhanced oil recovery by steam injection or geothermal applications cement damage by fatigue becomes a more important issue. In order to evaluate the behavior of this material, experiments were performed to investigate how cement reacts to cyclic loadings. A low number of cycles are referred to as up to 100 loadings sequences. Class G cement was chosen as being one of the most important cement types in Germany. Samples consisting of a pipe cement compound were tested by loading them cyclic with a hydraulic press. Their failure was analyzed by determining the stress distribution inside of the samples in analytical and numerical way. It has been found that fatigue of cement is rather similar for metal and cement at least in the low cycle range. For metals there is a specific stress limit where failure can occur within several cycles. This means if the limit is exceeded the material will fail, maybe not at the first cycle, but it will fail over the cycles. Cement shows this behavior similar to metals, no other fatigue mechanisms like damage accumulation were observed, just a straight load limit. Key words: Well cement; Low cycle fatigue; Class G; Experiment