Simulation Of Brine-gas-sandstone Interactions During Carbon Dioxide Geological Storage

Geological storage of carbon dioxide （CO₂） is one of the most promisingmethods for reducing anthropogenic CO₂emissions into the atmosphere. However,the research in China is still in the preliminary stage. In this study, CO₂geologicalstorage mechanisms were studied through high-pressure reactor experiments andnumerical simulation by means of PHREEQC and TOUGHREACT. The mainconclusions include:1、 The experimental results （experimental conditions:3days,52℃） indicatedthat there was calcite precipitate observed in the system. The calcite was formed byCa²⁺from the dissolution of dolomite and gypsum and (CO₃^2-in the system, whichwas caused by the formation of calcite. The SEM results also showed that there wascalcium mineral precipitate and erosion phenomenon at the surface of rock core. Withincrease of pressure from2to8MPa, the concentration of Ca²⁺and Mg²⁺increasedbut the amount of concentration of SO₄^2-was not changed. The reason is that thedecreased pH enhanced the dissolution of dolomite but did not affect the dissolutionof gypsum. The increase of initial concentration of NaCl from0.02to0.5mol/Lresulted in slight concentration increase of Ca²⁺, Mg²⁺and SO₄^2-, which was resultedfrom dissolution of gypsum and dolomite. Since there is no formation of dawsoniteobserved by X-ray diffractometer, the concentration of Na+decrease after reactionshould be studied further.2、 Based on the equilibrium simulation results, there is no effects of changes ofCO₂partial pressure （lgPCO₂=-1.5～1）,temperature （30℃～90℃）and initial NaClconcentration （0～2mol/L） on minerals of feldspar and clay. However, the changes ofthese factors have greater effects on reactions of calcite and dolomite. 3、 According to the results of dynamic simulation of TOUGHREACT, thepressure （2～20MPa） and initial NaCl concentration （0.5～2mol/L）did have nosignificant effects on dissolution and precipitation of clay minerals. There was effectof pressure on dolomite and maximum precipitation of was found when the pressurewas in the range from2to20MPa. With the increase of initial NaCl concentrationfrom0to2mol/L, the dissolution rate of dolomite was enhanced, which is beneficialto precipitation of ankerite but not to precipitation of calcite and magnesite. The trendof ion concentration change obtained from high pressure experiments is consistentwith the simulation results of TOUGHREACT. Based on the geological conditions,the simulated results indicated that the CO₂mineral storage capacity in Es4is higherthan that in Es3and the storage capacity is positively related with the content offeldspar and carbonate in the rock.