Semianalytical Solution for Plume Shape and Pressure Evolution During Injection in Deep Saline Formations

The injection of supercritical carbon dioxide ( in deep saline aquifers leads to the formation of a rich phase plume that tends to float over the resident brine. As pressure builds up, density will increase because of its high compressibility. Current analytical solutions do not account for compressibility and consider a volumetric injection rate that is uniformly distributed along the whole thickness of the aquifer, which is unrealistic. Furthermore, the slope of the pressure with respect to the logarithm of distance obtained from these solutions differs from that of numerical solutions. We develop a semianalytical solution for the plume geometry and fluid pressure evolution, accounting for compressibility and buoyancy effects in the injection well, so is not uniformly injected along the aquifer thickness. We formulate the problem in terms of a potential that facilitates solution in horizontal layers, with which we discretize the aquifer. Capillary pressure is considered at the interface between the rich phase and the aqueous phase. When a prescribed mass flow rate is injected, advances initially through the top portion of the aquifer. As is being injected, the plume advances not only laterally, but also vertically downwards. However, the plume does not necessarily occupy the whole thickness of the aquifer. We found that even in the cases in which the plume reaches the bottom of the aquifer, most of the injected enters the aquifer through the layers at the top. Both plume position and fluid pressure compare well with numerical simulations. This solution permits quick evaluations of the plume position and fluid pressure distribution when injecting supercritical in a deep saline aquifer.