Abstract
Changing the water-to-cement ratio is one of the major ways to develop cement slurry with different densities, which in turn will greatly affect the pore structure and mechanical properties of cement slurry. In the current study, the cement hydration model HYMOSTRUC3D was used to investigate the effects of water-to-cement (w/c) ratio (0.40, 0.44, 0.50) on the pore structure evolution and strength development of cement slurry. The microstructure of the cement stone was characterized via scanning electron microscope (SEM) and micro-computed tomography (micro-CT), and the mechanical strength of the cement stone was tested and analyzed via a mechanical tester. The simulated compressive strength and capillary porosity are in good agreement with the measured data, where the relative error between the simulated results and measured results are within 0.6~10.7% and 13.04~25.31%, respectively. The capillary porosity is proved as the main factor affecting the compressive strength of cement stone with different w/c ratios. Herein, the mathematical relationship between the measured capillary porosity and compressive strength could be well fitted via the mathematical prediction models of the Balshin function (R2 = 0.95), Ryshkewitch function (R2 = 0.94), Schiller function (R2 = 0.96), and the linear regression function (R2 = 0.95). Moreover, the linear regression function (y = −2.38x + 82.76) can be used to characterize and predict the quantitative relationship between the compressive strength and capillary porosity of cement stone. The findings in this study will provide a reference value in the fields of oil and gas cementing and building concrete.
Highlights
Cement slurry is typically utilized in filling the annular space between the pipe and rock formation, sealing casing columns, preventing formation series collusion, protecting production reservoirs, and stabilizing the oil and gas wells [1,2,3,4,5,6]
The compressive strength decreased with increasing w/c ratio and the cement content was of minor influence, while shrinkage and water absorption increased with the water–cement ratio and cement content
Li et al [13] established the relationship between compressive strength and total porosity of hardened cement paste with super low w/c ratios according to the Balshin function, Ryshkewitch function, and Schiller function
Summary
Cement slurry is typically utilized in filling the annular space between the pipe and rock formation, sealing casing columns, preventing formation series collusion, protecting production reservoirs, and stabilizing the oil and gas wells [1,2,3,4,5,6]. Li et al [13] established the relationship between compressive strength and total porosity of hardened cement paste with super low w/c ratios according to the Balshin function, Ryshkewitch function, and Schiller function. The HYMOSTRUC3D model was selected to simulate the hydration process and the microstructure development of cement slurry. The HYMOSTRUC3D and micro-CT models were selected to study the effects of the w/c ratio on pore structure evolution and strength development of cement slurry. With w/c ratios (0.40, 0.44, 0.50) and hydration times (1, 3, 7, 28, 140 days) were obtained from the cement slurry hydration kinetics model established on the HYMOSTRUC3D model [33], and the simulated results were compared with the measured results (mechanical tester and micro-CT). The findings of this study have certain application prospects in the fields of oil and gas cementing and building concrete
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