Development of a laboratory-scale numerical model to simulate the mechanical behaviour of deep saline reservoir rocks under varying salinity conditions in uniaxial and triaxial test environments

作者：Rathnaweera T D; Ranjith P G^*; Perera M S A; De Silva V R S

来源：Measurement, 2017, 101: 126-137.

DOI：10.1016/j.measurement.2017.01.015

• Laboratory-scale model
• Salinity
• Stiffness degradation
• Uniaxial
• Triaxial

maintenance of the long-term mechanical stability of the reservoir rock mass is essential in CO2 sequestration in deep saline aquifers. However, it cannot be confirmed without predicting the worst-case scenarios in saline aquifers, including high salinity conditions and the complexities caused by surrounding factors such as reservoir depth. Laboratory experiments to identify all such situations are difficult due to the advanced facilities required, and the associated cost and time. Therefore, numerical models play an important role in extending laboratory measurements for such complex and extreme situations. Although numerous numerical studies have been performed to date on field-scale conditions in saline aquifers, less consideration has been given to simulating laboratory data, which is important for up-scaling the data to field conditions. This study therefore aims to develop a laboratory-scale numerical model to simulate the mechanical behaviour of brine-saturated reservoir rock under triaxial stress laboratory conditions. The model validation was performed by measuring uniaxial and triaxial laboratory test data under 10-25 MPa confining pressures and the model was then used to investigate the influence of pore fluid salinity percentage on reservoir rock strength by considering various possible salinity levels (5%, 10%, 15%, 20%, 25% and 30% NaCl) and the influence of depth using a range of confining pressures from 10 to 100 MPa.
The proposed numerical model based on the stiffness degradation mechanism of reservoir rock can accurately simulate salinity-dependent stress-strain behaviour under any stress environment (uniaxial/triaxial). According to the model, both pore fluid salinity and confining stress add additional strength to the reservoir rock mass due to NaCl crystallization and pore shrinkage. Importantly, the model clearly shbws a reduction of the effect of pore fluid salinity on reservoir rock strength characteristics with increasing reservoir depth or confinement, mostly due to the more significant effective stress at such extreme depths. This provides an important finding on CO2 sequestration in saline aquifers: salinity-dependent strength alteration is not very important for extremely deep aquifers compared to shallow aquifers. Although this model has the capability to simulate the failure of reservoir rock under extreme pressure conditions, the simulation results show a small fluctuation near the post-peak stage due to the complexity of the damage mechanism caused by strain localization.

• 出版日期2017-4