Determining the viability, risks, and optimal locations of sequestering carbon dioxide (CO2) in the subsurface requires detailed knowledge of the complex interactions among CO2, rock matrix, and pore fluids under reservoir pressure and temperature. Many physical and chemical processes are known to occur both during and after geologic CO2 injection, including digenetic chemical reactions and associated permeability changes. Together with hydrated CO2, cations from brines may form solid-state carbonate minerals, ostensibly providing permanent sequestration.
Reported here are findings and comparison of five large coreflooding experimental series preformed on quarried and reservoir carbonates (limestone and dolomite) with co-injected or alternating injections of CO2 and brine at reservoir conditions. Metal chlorides were added as tracer components in injection brines for three tests and appeared in quantities well above natural levels in deposited carbonates in one test. Core segment porosity and permeability are reported to indicate dissolution and deposition. Cores were sectioned and analyzed by chemical and back-scattered electron imaging (BSEI) and chemical titration for compositional changes. In two tests fluid samples taken at reservoir conditions and neutron computed tomography (CT) were used to monitor changes in in-situ fluid compositions and the development of the 3-D porosity structure of the flooded cores, respectively.