## 1 Introduction and Objectives  
Reduction of greenhouse gas concentration in the atmosphere has been in the focus of scientific research over the last decades. One of the possible approaches is to capture CO\({}_{2}\) from large industrial sources and to storage it in deep geological formations [1; 2; 3; 4]. During this process, the CO\({}_{2}\) is injected into a formation of high porosity and permeability (reservoir), which is overlaid by an impermeable formation (seal). Sedimentary rocks--both of siliciclastic and carbonate composition--are especially suitable reservoirs due to their textural and mineralogical characteristics. The high porosity and permeability of many sedimentary formations are decisive factors to consider for the feasibility of CO\({}_{2}\) injection on a large scale [5]. The CO\({}_{2}\) injection is intended in a dense phase or in supercritical conditions (SC CO\({}_{2}\): \(P>73.8\) bar, \(T>31.7\)\({}^{\circ}\)C), which results in a significant volume reduction of the gas [1; 6]. These conditions occur naturally in reservoirs under 800 m depth. Injecting CO\({}_{2}\) into geological formations provokes a series of physical and chemical changes, which can significantly modify the reservoir properties [7]. Geochemical changes arise from the interaction of the minerals of the host rock, the fluids that occupy the pore space of the rock and the injected fluid (i.e., SC CO\({}_{2}\)). A first step of this interaction is the acidification of the pore water due to the dissolution of CO\({}_{2}\), after which a series of precipitation and dissolution events may take place in the rock-brine-CO\({}_{2}\) system depending principally on the mineralogical composition of the rock [8; 9; 10]. In carbonates, the acidified brine tends to dissolve calcite (CaCO\({}_{3}\)). This dissolution increases the Ca ion concentration in the brine, which creates favourable conditions for the precipitation of other solid phases. For example, if the brine contains relevant concentrations of sulphate ions, precipitation of gypsum (Ca SO\({}_{4}\)) could be possible [11]. This is a plausible situation as high salinity of the brine is one of the requirements for CO\({}_{2}\) storage [1], being this condition an indicator of a confined reservoir structure. A large number of laboratory experiments (both static and dynamic) have addressed the described rock-brine-SC CO\({}_{2}\) interaction [4; 12; 13; 14; 15]. These studies concluded that the rock porosity and permeability increase after CO\({}_{2}\) injection due to the dissolution of carbonate minerals (e.g., CaCO\({}_{3}\)). Notwithstanding, in other studies [15; 16; 17; 18; 19; 20], the porosity-permeability of the rock was decreased by the precipitation of new mineral phases (e.g., MgCO\({}_{3}\), CaCO\({}_{4}\)) even though carbonate dissolution also took place. A recent review paper [21] concluded that often contradictory results were published in the literature and that the \"uncertainty regarding injectivity alteration caused by salt precipitation is very high\". According to [7], the dissolution-precipitation ratio is controlled by the SC CO\({}_{2}\) dissolution in the brine, in other words by the saturation ranges of liquid (brine) versus gas (CO\({}_{2}\)) phases. CO\({}_{2}\)-rock interactions in dry or near dry conditions have also been studied [3; 22; 23]. These conditions are likely to occur during the injection phase in the close vicinity of the injection point (i.e., well), where the SC CO\({}_{2}\) displaces the brine and fills the rock pore space. Theoretical and experimental studies of rock--CO\({}_{2}\) interactions in dry conditions [3; 20; 24] indicate the absence of chemical reactions and, consequently, negligible textural-mineralogical-chemical changes. During CO\({}_{2}\) injection into a geological formation, zones of different saturation ranges of liquid and gas phases are formed in function of the distance to the injection point.