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Constitutive Modeling of Soft Sandstone Degradation under Cyclic Conditions Open Access


Other title
Bounding surface plasticity
Soft sandstone
Sand production
Type of item
Degree grantor
University of Alberta
Author or creator
Rahimi, Mojtaba
Supervisor and department
Nouri, Alireza (Department of Civil and Environmental Engineering)
Chan, Dave (Department of Civil and Environmental Engineering)
Examining committee member and department
Chan, Dave (Department of Civil and Environmental Engineering)
Adeeb, Samer (Department of Civil and Environmental Engineering)
Okuno, Ryosuke (Department of Civil and Environmental Engineering)
Deng, Lijun (Department of Civil and Environmental Engineering)
Nouri, Alireza (Department of Civil and Environmental Engineering)
Wan, Richard (Civil Engineering, The University of Calgary)
Department of Civil and Environmental Engineering
Petroleum Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The near wellbore region is subjected to cyclic loads due to repeated changes of the mean effective stress. These repeated loads result in plastic deformation and sanding problems which can occur in injection or production wells. The difficulty is more pronounced in weakly consolidated reservoirs since they are more prone to sanding. Therefore it is required to investigate the material response to cyclic loading. In this research, the mechanical behaviour of uncemented and cemented sands under monotonic and cyclic loading are studied. Emphasis is placed on the constitutive modeling. A critical state constitutive model which was developed at the University of Alberta for monotonic behavior of cohesionless sands was chosen as the base model. First with modification of the hardening law, plastic volumetric strain increment and unloading plastic modulus, the original model was modified to describe sand behavior under cyclic loading. The modified model was calibrated and validated against triaxial cyclic loading tests for Fuji River sand, Toyoura sand and Niigata sand. Comparison between the measured and predicted results suggests that the model can capture the main features of sands under cyclic loading. Second the original model was modified for cemented sands. Formulation of the yield function, elastic moduli, plastic modulus, flow rule and other components of the original model were modified. Having incorporated these changes, the radial mapping formulation of bounding surface plasticity was incorporated in the model. The modified model was assessed against monotonic triaxial tests. Third to simulate the mechanical behaviour of cemented sand/soft sandstone under cyclic loading, some further modifications were incorporated into the model. Destruction of the cementation bonds by plastic deformation was considered as the reason for the mechanical degradation of cemented sands. To model cyclic response, the unloading plastic and elastic moduli were formulated based on those of loading. The proposed model was evaluated against laboratory triaxial tests, and the model agreed with experimental observations. Fourth the application of the proposed constitutive model was ultimately extended to cases that are not under conventional triaxial conditions. This was performed by incorporating the inherent anisotropy and b-parameter into formulation of the proposed model.
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