Geomechanical modeling of salt cavern stability for carbon dioxide storage in the Maha arakham formation, northeastern Thailand

Abstract

In Thailand, CO2 emissions quadrupled over the past three decades since 1989, with the power generation sector as the main contributor by burning fossil fuels to produce electricity. Therefore, the power generating industry has come under scrutiny and been pressed by society to take responsibility. Carbon Capture and Storage (CCS) is one of the many methods to deal with CO2 emissions. Generally, CO2 is captured and stored in geological formations, e.g. rock salt deposits. Salt caverns have been intensively studied regarding their usage for CO2 storage because of their favourable characteristics. In this research, the Finite Element Method (FEM, ANSYS Student 2019 R2) was used to compute the optimum salt cavern shape that can be excavated by deep solution mining. Investigated shapes were spherical, teardrop, pear, bulb, and cylindrical shape. All of the caverns are designed to have a volume of ~520,000 m3, allowing for the storage of ~0.4 million tons of CO2 in its supercritical fluid state. The safety factor value and volume change were used as criteria to define which cavern shape is most suitable for CO2 storage. The area around drill hole K-89 in Ban Nong Plue, Borabue district, Maha Sarakham province, northeast Thailand, was chosen as location for CO2 storage because the sources of CO2 are in immediate vicinity of potential sinks. Input parameters used in the modeling process are cavern geometry, material properties (lithologies), and creep parameters of rock salt. The creep constitutive model used in this case study is the Norton creep power law which defines the steady-state stage of creep. The modeling steps follow the operation stages of CO2 storage, from the solution mining to the 500-year time span after cavern closure. The results indicate that the difference in the width in the upper part of the cavern (1/3 of the cavern height) influences the volume change. The smaller the width the lower the volume change, all caverns having the same height with the exception of the cylindrical cavern. Additionally, the results show that all the designed shapes have a safety factor value greater than 1, making them technically viable for being used as a Carbon Dioxide Storage in northeast Thailand. The optimum shape for storing CO2 in its supercritical fluid state, maximizing the cavern stability, is the teardrop shape with a safety factor value of 6.36, also exhibiting the lowest volume shrinkage (0.018%) of all investigated shapes.