In this work, an advanced numerical geochemical method, reactive transport modeling (RTM), is applied to simulate the iron carbonate formation during and post-acid stimulation. The code Toughreact is used for the prediction of the dynamic processes of reservoir fluid composition, and porosity and permeability alteration during and after stimulation treatment. This allows an insight into the spatial and temporal distribution of iron carbonate precipitation. Results of an acid treatment scenario in a sweet carbonate reservoir demonstrate that iron carbonate formation is a corrosion induced scale issue. High concentration of iron can release from tubular due to corrosion during acid injection stage, especially for high temperature reservoirs. The injected acid influenced an area of about 5 meters radial distance from the wellbore. The acid selectively dissolves limestone while leaving the dolomite component largely undissolved. A significant increase in porosity was observed in area of about 1 meter from the well due to the dissolution of limestone. Iron carbonate will not deposit at the initial stage of acid injection due to low pH environment. A significant amount of iron carbonate scale was observed in the acid-influenced area due to mixing of spent acid with the formation water.
This paper presents the mechanisms of iron carbonate deposition during acid stimulation in sweet carbonate reservoirs. It will contribute to applying iron carbonate scale prevention strategy and optimizing acid treatment design.