Abstract:

During the reaction between CO₂ and rocks, there is a synergistic/coupling effect among minerals because the rocks contain quartz, potassium feldspar, albite and other components, which promotes or inhibits the reaction process to a certain extent. The chlorite is an important clay mineral of sedimentary rocks. In order to clarify the chemical behavior and change process of the chlorite in the CO₂ aqueous solution, the state of chlorite reacting with CO₂ respectively for 7 and 30 days at 10 MPa and 60 ℃ are systematically evaluated by means of XRD（X-Ray Diffraction）, XRF（X-Ray Fluorescence）, ICP（Inductively Coupled Plasma）, and SEM（Scanning Electron Microscopy）, focusing on the comparison of the change of the solid elements, the crystal structure and the ion concentration in the reaction solution before and after chlorite powder reaction. Combined with the structural characteristics of chlorite, the mechanism of chlorite change is clarified. The results show that the concentrations of Ca²⁺, Mg²⁺ and Al³⁺ in the liquid phase firstly increase and then decrease after the reaction of the chlorite with CO₂. The concentration of Si⁴⁺ firstly increases and then is stabilized. The crystal planes corresponding to chlorite d（002） and d （004） peaks in the solid phase are destroyed after the reaction, and the mass ratio of Si and Al in the solid element increase from 4.82 to 5.39. Under the acidic conditions, hydroxyl groups in brucite flakes are easier to combine with H⁺ and release cations such as Fe²⁺, Mg²⁺, Al³⁺, etc. Because the brucite octahedron is more prone to ion exchange than silica tetrahedron and alumina octahedron, Mg, Al, Fe and other elements in brucite flakes are dissolved before Si and Al in silica tetrahedron and alumina octahedron.

Key words: chlorite, CO₂ flooding, XRD analysis, element analysis, ion concentration