Brine with designed ionic composition has been shown by many authors as a technique that improves oil recovery, allowing an increase of up to 20% of the total oil saturation of carbonates rocks samples during laboratory experiments. The main objective of this research is the development of an experimental methodology to assess the impact of the dissolution of carbonate rocks due to brine with designed ionic composition in high pressure environments, such as the ones found in Brazilian pre-salt reservoirs. This work reports the temporal effects of dissolution of outcrop carbonate rocks while in contact with water of different total salinities (38 kppm, 16 kppm, 8 kppm and 2 kppm) at 10,000 psi and 110° C, in terms of changes in mass, porosity and permeability. The experimental setup was composed of: positive displacement pump (DBR System), fluid injection cylinder, sample carrier cell, transducer pressure and oven to maintain the temperature of the system. The aforementioned samples were cleaned and dried in order to proceed with basic petrophysical characterization (porosity, permeability and weight). Outcrop rocks were placed inside pressure vessels containing water at the specified salinity and held under pressure for determined periods of time (168 hrs). At time intervals, the rock specimens were taken for evaluation of mass, porosity and permeability. Five cycles were repeated for different water total salinities. Changes on porosity and permeability were evaluated by gas porosimeter and gas permeabilimeter, respectively. Mass of the outcrop rocks were determined using analytical scale. Experiments showed that modifying water salinity can induce the carbonate dissolution which may be related with an ionic exchange between the ions present on the rock surface and the ions in the brine. A non-thermodynamic equilibrium state is created which results in chemical interactions in the aqueous phases as well as interactions between water and rock in terms of precipitation/dissolution of rock minerals and/or changing the rock surface charge resulting in loss of mass and changes on porosity and permeability of the samples. The research innovative approach consisted in the development of an experimental methodology to evaluate the effect of brine with designed ionic composition on the dissolution of outcrop carbonate rocks at high pressure and temperature in static conditions.

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