Mathematical And Physical Model Of Carbon Dioxide Geological Sequestration And Its Solution

Carbon dioxide capture and sequestration?CCS?technology is a promising approach to reduce carbon emission and to mitigate the greenhouse effect.The study of the migration of underground CO₂ and its effect on seismic response is of great importance to succefully implementing CO₂ geological sequestration.In this dissertation,reservoir simulation method,rock physics model and seismic modeling method are combined to systematically study the CO₂ geological problem.Based on mass conservation law and energy conservation law in porous media,a coupled mathematical model suitable for CO₂ sequestration modeling is obtained.Then the Biot model is re-established,and the wave field is decomposed and the Lame potential equations of the P-wave and S-wave are obtained.Based on these results,the effect of many rock physics parameters on the dispersion and attenuation properties of the rock saturated with water and CO₂ is studied.The numerical simulation results show that the porosity and saturation of CO₂ are the most important factors affecting the wave properties,and the change of porosity and saturation strongly affect the dispersion and attenuation of the fast P-wave,S-wave and slow P-wave.The velocity of the rock saturated with water and CO₂ is very sensitive to the changes of temperature and pressure at the critical point of CO₂.Second,based on the multi-component multi-phase flow model in porous media,the simulation of CO₂ radial flow and the simulation of CO₂ storage in 2D layerd model are preformed,and CO₂ saturation fluid pressure distrabution at different stages after sequestration are obtained.Through simulations using different relative permeability and capillary pressure functions,it can be found that the increase of relative permeability and capillary pressure is in favour of the horizontal flow of CO₂ and thus the distribution of CO₂ will be larger.Then,according to the reservoir simulation results and the Biot model with multi-phase flow,the seismic modeling research of CO₂ geological storage is performed.The synthetic seismograms at different stages of CO₂ storage are obtained using the SSM method for solving the wave equation in two phase media.The synthetic single-shot records and zero-offset resords show that the seismic response of the reservoir is strongly affected by the injected CO₂.In the synthetic zero-offset resords,the “push-down effect” is clearly observed and is consistent withmonitoring results of real CO₂ storage project,and relative permeability and capillary pressure have remarkable influence on seismic modeling results.Finally,reaervoir parameter inversion of real data is preformed using Biot model with multi-phase flow and the self-adaptive hybrid genetic algorithm,which is an inversion algorithm of better ability of anti-interference,local search and anti-premature.The inversion of core data confirms the validity of the algorithm and that the Biot model with multi-phase flow can well interprete the wave velocity property of the rock saturated with water and CO₂.The inversion study of the seismic modeling data of real CO₂ storage project shows the validity and effectiveness of reservoir parameter inversion using the Biot model with multi-phase flow and the self-adaptive hybrid genetic algorithm,it is expected to be widely used in the real seismic monitoring of CO₂ geological sequestration.