Rock fluid interactions during seawater injection in carbonates: An experimental evaluation on dolomitization and anhydrite precipitation

Carbonates are expected to be reactive during the injection of fluids as a secondary recovery method in an oilfield reservoir. Desulphated seawater is usually chosen to reduce scaling potential for barium and strontium sulfates at the producer wells. However, desulfation presents some operational difficulties, often limiting the platform injection’s capacity. The chemical interactions between seawater and carbonate reservoirs affect produced water composition and must be considered for scaling predictions. Reactive transport models had shown that dolomitization increases anhydrite precipitation, reducing sulphate concentration in the produced water. This paper studied the reaction between calcite and three different fluids: seawater, seawater without sulphate and seawater without magnesium. All tests were performed in the presence of CO₂ and using a semi-batch reactor. The focus was to analyze the effects of possible dolomitization on sulfate concentration in reservoir conditions. As the scale potential is strongly related to the sulphate concentration, the previous knowledge of this behaviour plays a key role at the water quality decision. Experimental results confirmed simulation predictions.