شهریار عصفوری

In this study geochemical behavior of CO2-natural brine-carbonate rock was investigated. At first, in order to assess the effect of gas on the brine. CO2 at atmospheric pressure was injected into brine without core sample in order to assess the effect of gas on the brine. Results show that pH of the system decreases due to injection and any precipitation was not observed at the end of experiment. In another set of experiments at different temperature and pressure (50-70? and 73.5-1100psi respectively) CO2 was injected into brine and rock in a stainless steel cylinder. Dissolution of rock and increasing in the amount of dominant rock cations were caused as a result of CO2 injection. In order to investigate changes in core samples due to probable reactions, physical properties of rock such as porosity and permeability, were measured before and after experiment. Comparing properties before and after experiments shows that secondary precipitation blocks the throat of porous rock and decrease permeability. Nonetheless porosity of some samples increase and others decreases. Since these reactions change the structure of reservoir rock they can decrease or improve reservoir permeability. Using geochemical reactions could help in estimating permeability changes. These results are extremely effective in estimating the injection rate and pressure of CO2 injection. Also, decreasing the amount of injected CO2 as a result of dissolution/precipitation reactions causes safe storage of this gas.