Characterization of Cement’s Temporal Mechanical Properties Under Simulated Downhole Conditions

Abstract The evolution of cement mechanical properties is crucial for the performance of zonal isolation and determining the wait-on-cement period. To address this, a triaxial testing facility is developed that directly measures cement static elastic modulus and Poisson’s ratio of cement under in situ conditions. The accuracy of this facility was validated by measuring the bulk modulus of water. To obtain the temporal evolution of cement mechanical properties, an unloading-loading cycle every 30 mins was used from the beginning to the end of the experiment. An amplitude of 10 MPa during cyclic loading guarantees that the cement is in the elastic stage. The theory of poroelasticity was applied to estimate cement elastic modulus and Poisson’s ratio. A 7-day experiment was conducted under axial stress cycling between 40 MPa and 30 MPa, with a confining stressof 25 MPa. The Class G Cement, with a water-cement ratio of 0.4,began to gel after curing for 350 minutes (min), with rapid strength growthoccurring between 400 to 2000 min. After this period, the cement’s elastic modulus stabilized between 47 and 55 Gigapascal (GPa), and its Poisson’s ratio reached 0.35. These values are significantly higher than those obtained from the conventional triaxial compression tests. Overall, our work provides one way to evaluate cement in situ mechanical properties, which can be highly valuable for geothermal and deepwater drilling applications.