This paper discusses the design of underground salt caverns, opened by solution mining, for CO2 sequestration in Brazil, considering the large thicknesses and continuity of rock salt overlying the pre-salt reservoirs. Rock salt has negligible porosity when compared to other geomaterials, which ensures sealing to most fluids and gases. It is also subject to the phenomenon of visco-plastic creep deformation and can tolerate high levels of strain without developing structural damage of its mineral skeleton. Another phenomenon is the process of self-healing, where cracks and faults are self-healed with time. Taking advantage of these properties, caverns developed by solution mining in salt domes may be used for storage of hydrocarbons and other products, for example CO2. Special attention is given to the geomechanical structural design of the caverns using computer codes developed for the simulation of excavations in salt rock formations, considering validated constitutive creep laws obtained by lab tests. The codes have being used in the design of several clusters of caverns for brine production, design of the underground conventional potash mine and in the design of the pre-salt oil wells, for the exploration and production of the pre-salt reservoirs. Despite being a technology already dominated worldwide, the use of underground storage of CO2 in salt caverns for offshore application in deep and ultra-deep water is unprecedented.
With the application of new technologies for processing and interpreting seismic data, PETROBRAS, in recent years, has achieved great success in the discovery of giant oil fields underlying thick layers of rock salt. The rock salt has negligible porosity when compared to other geomaterials, which ensures excellent sealing to most fluids and gases, even under high pressures. Rock salt is also subject to the phenomenon of visco-plastic creep deformation which develops in the time domain as the relaxation of the deviatoric or shear stresses, to the condition of steady-state equilibrium with constant creep strain rate and can tolerate high levels of strain without developing structural damage of its mineral skeleton. This phenomenon can be observed in nature in the sedimentary layers intercepted by salt domes or other structures associated with the natural movement of salt.