1. The influence of H2S and CO2on the triaxial behavior of Class G cement paste under elevated temperature and pressure
- Author
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Neves, Anderson Viana, Lima, Victor Nogueira, Lima, Igor Nogueira, Letichevsky, Sonia, de Avillez, Roberto Ribeiro, and de Andrade Silva, Flávio
- Abstract
Cementing is one of the most crucial operations in an oil well since it fixes the casing and prevents fluid migration across permeable zones. However, the material used in this process, Class G cement, faces exposure to various agents during and after its curing process, particularly at greater depths where temperatures and pressures are elevated. Exposure of this cement to elements like brine, H2S gas, and CO2gas tends to compromise the material's durability and the well's integrity. Consequently, exposure to these agents leads to modifications in the cement paste's physical, chemical, and mechanical properties. Thus, investigations into the influence of these agents are crucial to ensure the integrity of the cement sheath. In this study, Class G cement pastes were exposed for three months in an autoclave under elevated pressure (20 MPa) and temperature (88 °C) in a brine-saturated environment with either H2S or CO2at different stages. The research investigated mechanical behavior through uniaxial and triaxial compression tests, physical properties through porosity and micro-computerized tomography tests, and chemical properties through X-ray diffraction and pH tests. The study demonstrates that confining pressure significantly affects the deformation of samples exposed to brine+H2S and brine+CO2, causing plastic deformations at confining pressures above 20 MPa even before applying deviatoric stresses. Exposure to acidic gases also leads to a 27% reduction in compressive strength for brine+H2S and a 45% reduction for brine+CO2, affecting the elastic moduli due to potential micro-defects originating from the curing process and chemical reactions induced by the presence of the acidic gases.
- Published
- 2024
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