Research On The Evolution Of Geostress During The Geological Storage Of CO₂ In Low Permeability Reservoir

Carbon dioxide geological storage(CSS)as an effective measure to reduce the greenhouse gas effect,while reducing carbon dioxide emissions will also cause geological effects such as changes in in-situ stress and formation deformation.If it is not properly controlled,it will also cause CO2 channeling and even leakage.In this paper,based on the CO2 flooding project in an actual oil field,the fracture of carbonate rock under three-dimensional compression is analyzed from the micro perspective by the combination of laboratory experiment,theoretical modeling and numerical simulation.At the same time,the interaction between seepage and stress is taken into account.Using the subroutine function of ABAQUS/CAE,the carbon dioxide in geological storage is studied by numerical simulation and the evolution of parameters such as in-situ stress,reservoir displacement,pore pressure and permeability is analyzed.The influence of different injection pressure and formation pressure on formation deformation,carbon dioxide channeling and the possibility of leakage of injected gas in the reservoir are analyzed,which provides theoretical reference for improving the efficiency of geological storage of carbon dioxide and the safety of engineering implementation.The thesis includes the following parts:① A series of macro parameters such as porosity,permeability and compressive strength of a group of carbonate rock samples from the actual oil field were measured through laboratory rock mechanics experiments.The results show that carbonate rocks have high density and strength characteristics,and are good places for CO2 storage.② Using PFC particle flow numerical simulation software,combined with discrete element theory,the effect of each meso parameter on macro mechanical parameters was studied in detail,and the typical 43#carbonate rock was selected,combined with its permeability,porosity,compressive strength,Based on the results of laboratory experiments such as internal friction angle,porosity and stress-strain curve,a set of meso-parameters that can correctly reflect the structure relationship of the rock sample are obtained.On this basis,the numerical simulation of carbonate rock under triaxial compression is completed,and the failure process and stress and strain distribution of carbonate rock during triaxial compression are analyzed from a meso point of view.The results show that under the condition of three-dimensional compression,the carbonate rock mainly occurs shear failure,and the macro shear zone mainly occurs at the top of the rock,which is also the area with the largest distribution of stress and strain.③The percolation mechanism involved in CO2 geological storage and the digital model of CO2 geological storage are expounded.A simple reservoir model is established to calculate the carbon dioxide sequestration considering the seepage stress coupling model and the general rigid model,and the calculation results of stress,displacement,pore pressure,porosity and permeability rate are compared.The results show that the reservoir permeability,permeability rate and porosity under the influence of coupling have higher stress sensitivity,especially under the effect of high pressure injection,this phenomenon will be more obvious,so it is necessary to consider the effect of coupling in the actual calculation of CO2 storage.④The numerical simulation of carbon dioxide sequestration based on seepage stress coupling is completed.Firstly,the relevant geological model of wuqiyougou oilfield is established by using Petrel,which is transformed into a finite element model and imported into Abaqus/CAE for calculation.After that,the in-situ stress balance of the reservoir geological model is carried out,the numerical simulation of gas injection and storage process is completed,and a series of relevant conclusions are drawn.Finally,the influence of injection pressure and formation pressure on the sealing result is analyzed.The results show that the physical characteristics of the reservoir will change during the storage process,which may lead to rock damage and CO2 leakage.The greater the injection pressure,the more obvious the change in reservoir permeability and the greater the deformation of the formation uplift.Therefore,the gas injection pressure should be reasonably controlled during the storage process.The formation deformation is negatively related to the initial pore pressure of the formation.As the formation pressure increases with the increase of the depth of the reservoir,when storing CO2,under the premise of economic conditions,ensuring the depth of the reservoir can effectively reduce the damage to the formation and ensure the safety of CO2 storage.