The Influence Of The Mechanical Response Of The Reservoir On CO₂ Geological Storage

CO₂ geological storage is one of the most effective means about reduction of CO₂ emission.CO₂ is injected into the deep stratum,the injection pressure and temperature changes will change the stress state of the rock in the injected area,make the effective stress decreases,and formation porosity and permeability change,which will affect the CO₂ migration and injection capacity and storage potential and caprock sealing ability and so on.Based on the reservoir of Liujiagou Formation in CCS demonstration area of Ordos Basin,the influence of the mechanical response of CO₂ geological storage is studied by means of indoor experiment-statistical analysis and numerical simulation.The main result of paper are as follows:1.The relationship between pore pressure and permeability of the reservoir rock was studied by systematic experiments,and on this basis,through the statistical analysis method,the mathematical model of the two is determined.The experimental results of the relationship between pore pressure and rock permeability show that the pore pressure increase,and the permeability increases with the increase of pore pressure,in the set pore pressure range?4MPa-18MPa?,the pore pressure increases make the deformation of the rock pore structure is elastic deformation,the mathematical model of the exponential relationship between permeability and pore pressure is determined during the different period of pore pressure loading and unloading.and the theoretical basis is established for considering the reservoir mechanics response of the CO₂ geological reservoir process.2.TOUGH2 is one of the most commonly used simulation software for CO₂ geological storage,it is internationally recognized.In order to make full use of its advantages,in this paper,the mathematical model of the fluid were analyzed in TOUGH2,and use pressure and temperature parameters of the mathematical model in TOUGH2 as the coupling nodes,The mathematical model of pore pressure and rock permeability is coupled into TOUGH2 simulation software by partial coupling method,which realizes the function of software to consider the influence of reservoir mechanical response in the simulation of carbon dioxide injection.3.Through the numerical simulation technology to systematically analyzed the influence of the mechanical response for reservoir environmental characteristics?pressure,temperature?,physical properties?porosity,permeability?and the elements of CO₂ geological storage?reservoir pressure field distribution and migration,injection rate,CO₂ storage?in the process of CO₂ injection.The following conclusions:The results show that considering the reservoir mechanics response can promote the diffusion of reservoir pressure outward,but the impact of reservoir temperature transfer is very small,for the design scheme which is the injection pressure is higher than the formation pressure 3MPa,CO₂ injection of 5 years,considering the mechanical response,the reservoir pressure is increased by about 0.06 MPa,in the vicinity of the injection wells,the porosity and permeability of the reservoir are increased by about 0.3% and 10%,and the CO₂ migration distance is increased by 8%,The CO₂ average injection rate and storage has increased by 6.8% It can be seen that the reservoir mechanics response has little effect on reservoir pressure and porosity for injection of 5 years,but it has a significant effect on reservoir permeability,CO₂ migration distance,CO₂ injection rate and storage.Comparison of the design scheme of different injection pressure,when the injection pressure from higher than formation pressure 1MPa to 5MPa,the mechanical response of the reservoir makes the largest amount of reservoir pressure from 0.01 MPa to 0.17 MPa,the biggest increase rate of porosity of the reservoir from 0.1% to 0.5%,the biggest increase rate of permeability of the reservoir from 3% to 17%,the increase rate of the CO₂ gas migration distance from 5% to 13%;the increase rate of the CO₂ average injection rate and storage from 2.8% to 11.6%.With the increase of injection pressure,it can be seen that the influence of the mechanical response for reservoir pressure,porosity and permeability,CO₂ migration distance,CO₂ injection rate and storage becomes stronger,in the set injection pressure range,the greater the injection pressure,the influence of the mechanical response is stronger,it is a positive gain relationship.The results show that it is necessary to consider the influence of reservoir mechanics response when evaluating the efficiency,potential and safety of CO₂ geological storage.The research of this aspect has practical significance.