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Multiscale characterization of oilwell cement cured under HPHT conditions
(OnePetro, 2021) Qin, Jiankun; Pang, Xueyu; Zhang, Zhen; Fikeni, Kenedy Geofrey
As a complex composite material, the macroscopic mechanical property of oilwell cement is determined by its microscopic mechanical properties. During this study, the properties of oilwell cement specimens cured under high pressure and high temperature (HPHT) conditions were evaluated at both macro- and microscales. Short-term sonic strength analysis suggested that the HPHT strength retrogression occurred in the early stage. Specimens were cured at 200°C and 150MPa for different time periods of 14d, 30d, and 69d, to study the long-term mechanical property stability of silica-enriched oil well cement systems. Uniaxial compression tests were conducted on 25mm × 50 mm cylindrical specimens for macroscopic characterization of strength, modulus, and Poisson's ratio. Furthermore, microscopic testing was conducted using X-ray diffraction, mercury intrusion, and nano-indenter. Test results revealed that the damage during experiment may significantly influence the macroscopic properties of oilwell cement, but it had little effect on the microscopic level. On the micro-scale, the deterioration is characterized by increases in the proportion of a low-modulus and low-hardness phase. Additionally, the dependences of nanoindentation test results on testing parameters such as maximum load and appropriate grid size were also evaluated.