APPLICATION OF THE GOUY-CHAPMAN THEORY TO ANALYZE THE DEFORMATION OF THE CAPROCK DURING THE INJECTION OF CO2 IN DEEP SALINE AQUIFERS

With the entry into force of the Kyoto Protocol, the geological sequestration of CO2 is one of the technologies that can considerably reduce emissions of the main greenhouse gases in the atmosphere. It consists of the injection of CO2 in supercritical condition within reserves covered by low-permeability formations (caprock) able to prevent the flow of lift of the injected fluid, which supercritical state is less dense than water and tends to float moving towards the surface. In a realistic situation of seizure in an industrial plant, the injection speed must be such as to permit the disposal of all the captured CO2, in this context it is essential to the evaluation of the maximum pressure to which it is possible to perform the injection without the generate rupture phenomena in materials, and do not cause deformation on the surface such as to compromise the integrity of the existing structures. Under these conditions, this work has focused on the possibility of being able to consider the behavior of the caprock, such as a layer of cohesive soil that absorbs and transfers the displacement due to the expansion of the aquifer subject to the action of the flow of CO2 at high pressure, but lower than the overburden of the geological formations overlying the caprock. Assuming a caprock saturated unconfined laterally, which drains over time overpressure neutral interstitial fluid present in the matrix of cohesive soils, it has been calculated at the rate derived from the elastic yielding of consolidation theory of Terzaghi [1925] and compared this value with the one obtained by applying a coefficient of "consolidation" built on Sridaran & Jayadeva [1982] through the theory of the "double layer". This theory also known as the Gouy-Chapman [1910] was applied to the prediction of the behavior of cohesive soils where it conducted a micro-mechanistic approach. From the design point of view, this study would simulate the possibility of combining in a single integrated system, the injection of CO2 in the aquifer-tank with the possible slopes for mechanical effect of geothermal fluids contained in the interstitial caprock, in order to control the effects attributable to deformations induced due to the injection of CO2 under pressure.