Research On Percolation Mechanism And Application Of Conversion Of A Gas Condensate Reservoir Into Underground Storage

With the gradual increase of natural gas demand,more and more attention has been paid to the construction and related research of gas storage at home and abroad.Compared with foreign countries,the development of gas storage in our country is relatively late.The related research on the conversion of a gas condensate reservoir with edge water into underground storage is not deep enough.The effects of water on the phase of the gas condensate reservoir,reservoir heterogeneity on percolation and storage capacity,gas-oil diffusion and gas-gas diffusion on operation of gas storage when the formation pressure is lower than the dew point pressure are few.Therefore,this paper mainly studies the theory on percolation mechanism and application of the conversion of wen 96 gas condensate reservoir into underground storage.In order to study fluid phase,percolation mechanism and diffusion mechanism of gas injection and production of conversion of condensate gas reservoir into gas storage.The Wen 96 gas reservoir is taken as the study object.Firstly,the influence of reservoir fluid phase and water on the phase diagram of condensate gas reservoir has been studied.Secondly,stress sensitivity tests of multiple pressure buildup and dropdown,gas-water relative permeability of gas-water interaction,storage and flow capacity of multiple injection and production have been tested on the actual cores.The experimental test method of molecular diffusion of multi-component gases and actual crude oil in porous media has been established,gas-oil diffusion tests and hydrocarbon gas diffusion tests have been conducted in the sand packs.Thirdly,numerical simulation which simulated the process of converting the condensate gas reservoir into gas storage and considered influence of diffusion has been carried on numerical simulation software(Eclipse).The research results will play a positive role in further guiding the construction,storage capacity,parameter optimization design and emergency peak capacity of wen 96 underground gas storage.Main achievements are as follows:(1)Establish the experimental test method of molecular diffusion between multicomponent gas and actual crude oil in porous media,and dry gas-condensate oil diffusion coefficient has been measured.At the same time,the hydrocarbon gas diffusion coefficient in actual core was tested,and the effects of irreducible water saturation and physical property on the diffusion coefficient have been studied.(2)The numerical simulation study of gas-oil diffusion and gas-gas diffusion is carried out.The results show that the stronger the diffusion,the smaller the injection pressure,the greater the diffusion coefficient and the larger the storage capacity in the stage of gas storage.In the stage of gas production,the larger the diffusion coefficient is,the smaller the cumulative gas production is.Considering the diffusion,the larger the daily gas production is,the smaller the decline degree of reservoir pressure is.Considering the effect of diffusion,the emergency peak capability of gas storage is obviously weakened,and the requirement of emergency peak capability should be reached under higher formation pressure.(3)The effect of interlayer heterogeneity on percolation and storage capacity is studied by the core parallel experiment.The results show that the interlayer heterogeneity of gas storage reservoir makes fingering phenomenon very obvious.In the process of gas-water interaction,gas is more prone to import high permeability reservoir.This heterogeneity has little effect on the gas storage capacity.The percolation ability has a significant enhancement.(4)The influence of water on the fluid phase diagram of condensate gas reservoir has been studied.In the new phase diagram,the traditional oil-gas two-phase area is redivided into three-phase area including oil-gas-water three-phase area and oil-gas two-phase area.By studying the influence of different water content on the phase diagram,the phase diagram will be deformed seriously near the three-phase point when the water content of the condensate gas system is large.(5)The dynamic analysis of gas storage has carried out to verify the influence of interlayer interference and diffusion on the operation of gas storage.A systematic research,which includs the fluid phase,Percolation mechanism and diffusion mechanism of injection and production,numerical simulation of the operation of gas storage of conversion of condensate gas reservoir into gas storage,has been conducted in this paper.It has important theoretical and practical significance to the further study of this kind of gas storage.