Integrity Evaluation Of Underground Hydrogen Storage Traps In Aquifers

Hydrogen,as a zero-carbon,secondary clean and efficient energy,can be used as an alternative energy source for oil and natural gas,reducing the dependence on fossil energy.The site selection and trap integrity evaluation of underground hydrogen storage tanks are the technical issues for promoting hydrogen energy“neck-stuck”.By investigating the current situation of underground hydrogen storage in foreign countries and the current situation of natural gas storage in domestic aquifers,the similarities and differences between aquifer hydrogen storage and natural gas storage are analyzed,and the ’ two-step method ’ of site selection evaluation under the condition of ’ less data ’ is proposed.Based on the analytic hierarchy process,the site selection evaluation system of aquifer underground hydrogen storage is established.Secondly,the research status of foreign hydrogen underground storage cap rocks is summarized,the key factors affecting the sealing of cap rocks are screened,and the static sealing evaluation system of cap rocks is established.The dynamic and static sealing laboratory tests are carried out for the actual drilling cores in the study area,and the dynamic and static sealing ability of cap rocks in the target area of the project is verified.Finally,based on the engineering background of Y water-bearing trap,combined with literature research,evaluation system,laboratory test and finite element numerical simulation,the change of disturbance stress field of hydrogen underground trap is studied,and the mechanical integrity of reservoir,cap rock and fault in trap under seepage-stress is comprehensively evaluated,which provides theoretical support for site selection and safety evaluation of underground hydrogen storage in aquifer.This thesis mainly draws the following conclusions :The results show that :(1)The analytic hierarchy process is used to construct the evaluation system of aquifer hydrogen storage site selection from three aspects : site selection technology,geological safety and economic factors.The established evaluation system of aquifer hydrogen storage site selection is applied to Y water-bearing trap.(2)The static sealing evaluation model of cap rock is established,which includes nine items such as sedimentary environment,mineral composition and formation water acidity and alkalinity.The application of cap rock of Y water-bearing trap shows that the static sealing of cap rock of Y water-bearing trap is good.The dynamic and static sealing test of actual core of cap rock proves that the cap rock of Y water-bearing trap has good sealing ability.(3)he stress field of trap is not evenly distributed,the stress field of reservoir and the interface between reservoir and cap rock is the most disturbed,and the pore pressure diffuses rapidly and changes little in the vertical range.The stress path factor changes greatly at the interface between reservoir and cap rock.The total horizontal stress and total vertical stress path factor are smaller than the analytical solution in the gas injection stage and gas production stage in the reservoir region.The shear stress field twists in the gas injection and gas production stage,and the stress path factor changes greatly.(4)The change of cap porosity is greater than that of permeability and elastic modulus,the increment of horizontal total stress is greater than that of shear stress and vertical total stress,and the change of cap physical and mechanical parameters has little effect on it.(5)According to the rock mechanics test of cap rock,the rock mechanics characteristics of cap rock are better,and the possibility of rock failure is less under the injection-mining condition.(6)Surface uplift occurs during hydrogen injection and production,and the maximum displacement is 23.4cm in the first year of gas injection,which is relatively large.Therefore,mechanical integrity analysis should be further carried out.(7)During the injection and production of Y water-bearing trap,no tensile and shear failure occurred in reservoir,cap and fault,and no instability occurred in key fault,no leakage of the trap occurred.