JACQUEMET Nicolas

The oil industry is considering geological sequestration of carbon dioxide (CO2) and hydrogen sulphide (H2S) as a solution to store these gases permanently. It consists of injecting them into deep geological reservoirs via wells. These wells, made of steel tubes surrounded by a cement liner, can be degraded and constitute leakage paths. Various experiments have simulated the aging of these two materials. A specific experimental and analytical protocol was set up. The numerical simulation of cement aging was also addressed. Cement and steel are altered in contact with various fluid phases at 500 bar-120°C and 500 bar-200°C: a brine, a brine loaded with H2S-CO2, a mixture of brine + supercritical phase with H2S-CO2 and a supercritical phase with H2S-CO2 in the absence of liquid water. In these three cases, two decoupled reactions are observed: carbonation of cement by CO2 and sulfidation of steel by H2S. It appears that carbonation is maximal and sulfidation is minimal in the supercritical phase in the absence of liquid water. The textural and porosity properties of the cement are little or not affected by all treatments at 120°C. Porosity is even reduced in the presence of H2S-CO2. However, at 200°C, these properties are affected by the presence of liquid water in the medium. At this temperature, only the aging of the cement in the supercritical phase without liquid water improves its properties. Under all the conditions tested, steel is always corroded, and is therefore the most vulnerable material in the wells.