Influence of testing temperature and pressure on the mechanical behavior of well cementing materials

Abstract

In order to obtain insights into the mechanical responses of well cementing materials under various service conditions and provide more precise guidance for well cementing design, the mechanical behavior of a silica-enriched well cement system was investigated at various temperatures, pressures and drying conditions. Prior to mechanical testing, ultrasonic strength tests and a series of microscopic tests were conducted to verify that the silica-cement system cured at 150 °C/20.7 MPa exhibited stable properties with limited risk of strength retrogression. Triaxial tests conducted at ambient temperature (25 °C) demonstrate that the well cement exhibited an increase of peak strength and plasticity with increasing confining pressure, particularly under dry conditions. Additionally, brittle to ductile transition is more readily achieved for dried samples. However, the simultaneous application of both high temperature and high confining pressure (150 °C/30 MPa) resulted in reduced yield stress of the well cement, possibly because the weakening effect of high temperature overpowers the strengthening effect of high confining pressure. The peak strength and yield stress of the well cement increased significantly with the reduction of water content. The plasticity of the well cement increased upon the removal of evaporable water, but decreased with the removal of nonevaporable C–S–H bound water.

Keywords

• Well cement
• High temperature
• Confining pressure
• Uniaxial compression
• Triaxial compression
• Mechanical behavior