Study On Sealing Property Of Subsurface Buried Cap In Supercritical CO₂ Brine Layer

In recent decades,the greenhouse effect is becoming more and more serious due to the increasing emission of carbon dioxide.At present,one of the most important and effective ways to deal with carbon dioxide is to implement the geological storage of carbon dioxide,which can not only improve the recovery rate but also reduce the pollution caused by carbon dioxide to the environment.Because of its wide distribution and large reserves,the underground brine layer becomes an important area for carbon dioxide storage.In this paper,the sealing property of underground buried cap layer of supercritical carbon dioxide brine layer is taken as the research object.Firstly,the changes of porosity and permeability of cap rocks and minerals in different periods are measured by experimental means,and the changes of compressive strength of cap rocks in different periods are analyzed.On this basis,a saline reservoir model under heterogeneous texture was established in the study area.Numerical simulation method was used to study the physical property changes of reservoir and cap rock at different CO₂ injection rates under the condition of real reservoir model,so as to determine the stability of cap rock.The results show that the core porosity and permeability increase after soaking.The increase of porosity leads to the decrease of compressive strength of cap rock sample.In the process of continuous CO₂ injection,CO₂ migrates to the bottom of cap bed under the action of displacement pressure and gravity,which destroys the original mechanical balance of cap bed.The dissolution effect of carbon dioxide aqueous solution on cap layer is increasing,and the fracture risk of cap layer is also increasing with the high local pressure in the injection process.When CO₂ injection is stopped,the reservoir cannot reach the new stability in a short time due to CO₂ injection,and the CO₂-water-rock reaction will continue to increase the porosity and permeability of the reservoir to varying degrees.As can be seen from the overall simulation results of 100 years,the cap layer is affected by carbon dioxide dissolution and the thickness about 20 meters,which has a certain impact on the sealing property of the cap layer.