Study On The Monitoring Techniques Of Soil Moisture And Surface Deformation In CO₂-EOR Areas Based On Spaceborne SAR

CO₂-Enhanced Oil Recovery?CO₂-EOR?project needs a multi-platform joint monitoring system to ensure the safety of CO₂ storage and reduce the risk of leakage.Synthetic Aperture Radar?SAR?technology can provide a global scan land monitoring service with all-weather,all-day,and continuous space coverage.However,the research on SAR technology is insufficient in CO₂-EOR storage areas.In view of this,the thesis focuses on the key technologies of soil moisture inversion and surface deformation monitoring in CO₂-EOR storage areas based on spaceborne SAR.The inversion model and monitoring method are improved according to the surface scattering characteristics of the storage areas.And then the techniques of soil moisture inversion and time series deformation monitoring for storage areas with complex terrain are developed.Affected by complex and varied topography,there is a deviation between the real incident angle received by the scatterer in the storage areas and the incident angle of radar parameters.Aiming at this matter,the modified model is established by the geometric relations of satellite heading angle,incident angle of SAR and the space position of the surface scatterer to correct the real incident angle received by the surface scatterer.The relationship among backscatter coefficient of VV polarization,soil moisture,incident angle of electromagnetic waves and surface roughness parameters is simulated by Advanced Integrated Equation Model?AIEM?for Sentinel-1A parameters at the bare land surface.The synthetic surface roughness parameter is eliminated by utilizing VV/VH microwave models.And a single-variable soil moisture inversion model is established based on dual-polarization radar backscattering coefficient characteristic.The surface micro-deformation monitoring is limited by the spatial distribution density of the stable scatterer,especially in CO₂-EOR storage areas.To address this,an improved algorithm is proposed based on temporarily coherent targets?TCT?which maintain high coherence of partial observation period and whose spatial distribution is rich in CO₂-EOR storage areas.To preserve the TCT which can be distinguished by dual-threshold method,the algorithm regroup the interferometric pair by coherence of SAR image.After mining,decomposing and separating the interferometric phase information by multi-differential process,and reduing the phase contribution of lowcoherence interference pairs by temporal coherence parameters,the deformation velocity of TCT is inversed in CO₂-EOR storage areas.To verifying and analyzing the soil moisture inversion model and the microdeformation monitoring algorithm,CO₂-EOR demonstration area of Yanchang Petroleum in Jingbian county is adopted as a monitoring application area.The results of leakage risk assessment show that: 1)It shows a high accuracy level of soil moisture inversion model by dual-polarized SAR images in storage areas with complex terrain.Compared with field measurements,soil moisture retrieved from the model displays a fine accuracy,with R2 reaching 0.9362.The root mean square relative error of the 43 verification points is 0.963%,of which the absolute error of 24 points is between-0.5⁰.5,accounting for 56%.2)Multitemporal analysis method of temporarily coherent targets can significantly increase the spatial distribution density of monitoring targets,as well as improve the monitoring ability of surface deformation in the storage areas.81/m₂ distribution density of monitoring target identified by TCT algorithm increases 376% compared to PSIn SAR.Through the comparison and analysis of the results between TCT and classic PSIn SAR,the results show that the monitoring deformation velocities of TCT and PS have strong consistency,while the root mean square error being 6.01mm/a and the standard deviation being 5.97mm/a.3)Both of the soil moisture spatial distribution and the surface deformation trend is regular,which indicates that not only CO₂ leakage didn't occurred but also the risk of CO₂ leakage is low in the storage areas.By the influence of global constraints and local conditions,the spatial distribution of surface soil moisture shows spatial correlation,which means soil moisture don't have a significant abrupt change compared with the surrounding areas.On the surface deformation side,there is no large-scale trend surface deformation in the storage areas,which illustrates that the CO₂ storage of the Qiaojiawa CO₂-EOR demonstration area is being safe.