Corrosion Mechanism on Oilwell Cement in Formation Water with High Content of CO₂&H₂S

Abstract

Usually, marine carbonate gas reservoirs contain formation water with high content of CO2&H2S, It is difficult to satisfy the requirement of cementing quality in the gas reseroirs exploration due to the corrosion effect of formation water on cement. In this thesis, corroding tests of cement in formation water, which derived from a development well in northeast Sichuan province, were based on the simulation environment condition of 90°C under 0.1 MPa, 5 MPa and 10Mpa. Performances of cement including mineral composition, microstructure and permeability before and after corrosion were measured by TG-DTA, SEM, XRD and gas permeability and porosity of dense rock core tester. The results show that main corrosion products of cement being corroded in formation water with high content of CO2&H2S are ettringite, CaCO3 and CaSO4, both strength reduction and gradual rising of permeability can occur as testing pressure increasing. Accordingly, the corrosion mechanism and the damage process of cement under formation water with high content of CO2&H2S are expounded in the end.