Abstract Carbon capture and storage (CCS) has been proposed to mitigate the accumulation of CO2 in the atmosphere. Water alternating gas (WAG) technique is used in the industry to inject CO2 into underground formations either in sequestration or in EOR. CO2 dissolves in water, generating carbonic acid, which dissolves carbonate rock. The composition of the water is a critical factor that affects the rock permeability during sequestration. Sulfate content of the injected water can cause precipitation of calcium sulfate, which can negatively affect the rock permeability. This paper addresses potential formation damage due to sulfate precipitation during CO2 sequestration.
A core flood study was conducted using limestone cores. CO2 was injected at pressure greater than 1300 psi and temperatures (70 and 200°F). CO2 and brines were injected in WAG cycles under injection rates of 2 and 5 cm3/min. Seawater and formation brine were examined in this study. Core effluent samples were collected and concentrations of calcium and sulfate ions were measured to assess calcium sulfate precipitation. Core permeability was measured before and after the experiment.
The results show that temperature is the main parameter that affects sulfate precipitation during CO2 sequestration. Injection rate doesn't have a significant effect on the core permeability. At high salinity calcium sulfate precipitation occurs even with low sulfate concentration present.
Introduction CO2 sequestration is widely used to reduce the emission of CO2 into the atmosphere. CO2 can be sequestrated in deep saline aquifers, salt caverns, abundant gas storage faculties, depleted oil and gas reservoirs, enhanced oil recovery (EOR) projects, enhanced coal bed methane (ECBM), or unminable coal bed seams. Sleipner project in Norway is an example of CO2 sequestration in a saline aquifer. The total storage capacity planned for this project is 20 Mt CO2. Salt Creek and Weyburn in USA and Canada are two large CO2-EOR projects that have storage capacity of 27 and 20 Mt CO2, respectively. Yubari Project in Japan is a CO2- ECBM project that has a storage capacity of 200 t CO2. Salah project in Algeria is one of the most important CO2 sequestration projects in depleted hydrocarbon reservoirs in the Middle East. It has a storage capacity of 17 Mt CO2 (IPCC 2005).
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