| Popis: |
In the near future, the production of oilfields with high contents of associated sour gases will increase. Research on technologies to produce such fields are therefore of utmost importance. Due to the presence of corrosive gas, special attention has to be paid to the design of well materials (casing, cementing materials). However, published data on degradation mechanisms of cement-based materials exposed to H2S environments are very scarce. When placed in contact with acid fluid, portland cement will dissolve and become, at some time, fully degraded. In this case, the zonal isolation will be no more effective. New solutions are required to ensure long-term integrity of cementing materials. One potential solution is to incorporate chemicals in the cementitious matrix. The key idea is to incorporate additives that react preferentially with H2S and not with hydrated phases of the cement. The goal of this work was to assess this solution. The paper is dealing with cement formulations that incorporate mineral admixtures. These mineral admixtures have been chosen because of their high chemical affinity with hydrogen sulphide. We first give properties (density, compressive strength, rheological behaviour) of the novel formulations. Then we describe the static ageing tests performed in H2S-saturated brine at 120°C and 15 MPa. By combining different analytical techniques, the chemical evolution of the new formulations has been investigated. The results are dependent on the nature of the reactive mineral admixture. We show that, in some particular case, the incorporation of specific mineral admixtures leads to a strong damaging effect for the cement matrix. Consequently, for the design of H2S-resistant cement, these specific mineral admixtures should be discarded. The proposed solution (addition of reactive chemicals) is promising but requires more investigation in order to carefully control the reactivity of the different chemical species. |
