Research On The Variation Of Pore Throat During CO₂ Injection In Tight Sandstone Oil Reservoir

Recently,the technology of CO₂ injection in tight sandstone reservoir to improve oil recovery has become a hot topic.However,when CO₂ is injected into the formation,a series of complex chemical reactions will occur with formation water and rocks,which will affect the physical properties of reservoir rocks and the size distribution of pore throat.Focusing on this problem,The CO₂-formation water-rock reaction in tight sandstone reservoir is studied experimentally.We injected CO₂ into the saturated formation water tight sandstone core,and the core analysis method based on Nuclear Magnetic Resonance?NMR?was used to summarize and analyze the variation rules of pore throat before and after CO₂injection.A total of 4 groups of comparison experiments were designed,respectively comparing the reaction time,injection pressure,temperature and injection mode,and comparing the formation water ion concentration before and after the reaction.It was found that:After the injection of CO₂,the precipitates generated by the reaction may block the larger pores.When the temperature and pressure were changed,the total pore volume increased.At the same time,carbonate minerals and feldspar minerals were dissolved in the reaction process,and Na⁺,K⁺,Ca²⁺and Mg²⁺ions in the produced solution were increased to varying degrees.The migration and aggregation that occurred were likely to cause blockage of narrow pores and throat.According to the changes of porosity and permeability,this process will affect the permeability of the fluid in the reservoir rock and also affect the porosity to some extent.The influencing factors are closely related to temperature and pressure.This paper preliminarily explores the microcosmic mechanism of pore throat changes in reservoirs,and the obtained experimental data and results are of certain reference value to the water-rock reactions and pore throat changes that may occur in tight sandstone reservoirs during the mining process.