Study On Enhancing The Migration Of The Remediation Agents In Low Permeability Formation By Using Weak Gel

In the repair process of low-permeability lens contaminated sites,the remediation agent will flow around when it encounters the lens,so the utilization rate of the remediation agent is low.When repaired by extraction processing,the contaminants in the lens will cause tailing,which may cause the contaminants in the low permeability zone is difficult to removed effectively.The contrast of hydraulic conductivity is the ratio of the permeability of the high permeability background zone and the permeability of low permeability zone in the heterogeneous formation.It is an important factor affecting the migration of the remediation agents and contaminants in the lens.This paper proposes a weak gel technology,which blocks the large pores of the medium by weak gel,changing the contrasts of hydraulic conductivity of the heterogeneous formation for enhancing the migration rate of the remediation agent in the lens and improving the utilization rate of the remediation agent.In this paper,the influence of contrasts of hydraulic conductivity on the migration of remediation agents and contaminants in the lens and the preparation conditions of weak gel materials are studied.The simulation test is carried out to verify the effect of weak gel on the the contrast of hydraulic conductivity of heterogeneous aquifer and its ability to enhance the migration of remediation agents in low-permeability lens.The main conclusions are as follows:?1?The difficulty of the remediation agent enteringin the lens depends not only on the permeability of the lens'medium but also on the permeability of the background medium and the contrast of hydraulic conductivity of the two media.At the same time and similar contrast of hydraulic conductivity,the spreading rate of the remediation agent in the lens body with the background medium being coarse sand is larger than that of the background medium being grave,because remediation agents are more likely to cause flow around the lens with the background medium being gravel.?2?Results showed that the remediation agent migration speed got slower as the contrast of hydraulic conductivity increased,and when the background medium is the gravel,the time of remediation agent's spreading rate getting 100%in the lens increased from 8 to 360 hours when the contrasts of hydraulic conductivity increased from 3 to 52 at a natural groundwater flow rate of 0.5m/d,and when the background media is the coarse sand,the time of remediation agent's spreading rate getting 100%increased from 14 to 336 hours when the contrast of hydraulic conductivity increased from 5 to 130.The quantitative relationship above the spreading rate of the remediation agent and the contrast of hydraulic conductivity and the injection time is expressed as:Z₁=(109.623/K²_bl+1.035/K_bl+0.447)t when the background media is the gravel and Z₂=(92.208/K²_bl+17.247/K_bl+0.327)t when the background media is the coarse sand.According to this model,a theoretical basis is provided for the injection time node of the remediation agent.?3?In the process of the simulated extraction process,the flushing rate of the contaminant decreases with the increase of the contrast of hydraulic conductivity;When the background medium is gravel,the time of contaminant's flushing rate getting 100%increased from 13 to 480 hours when the contrast of hydraulic conductivity increased from 3 to 52,and when the background medium is the coarse sand,the time of contaminant's flushing rate getting 100%increased from 17 to 552hours when the contrast of hydraulic conductivity increased from 5 to 130.The function of flushing rate of the contaminant and contrast of hydraulic conductivity with the time could be expressed as:Z₁'=(54.999/K²_bl+6.605/K_bl+0.098)t,when the background media is the gravel and Z₂'=(78.875/K²_bl+16.374/K_bl+0.017)t when the background medium is the coarse sand.According to this model,a theoretical basis is provided for the time node of the extraction process.And when the time and the contrast of hydraulic conductivity are same,the flushing rate of the contaminant in the lens when the background medium is coarse sand is larger than that the background medium is gravel.Comparing the two processes of contaminant entering the lens and removing out of the lens,it can be found that the entering and removal process of the contaminant in the heterogeneous aquifer is irreversible in terms of time.Under the same conditions,the entry rate of the contaminant was always lager than the removal rate.when the background medium is gravel,the time difference increased gradually from 5 to 120 hours with the increase of the contrast of hydraulic conductivity,and when the background medium is coarse sand,the time difference increased gradually from 3 to 216 hours,which means the tailing effect becoming more and more obvious with the increase of the contrast of hydraulic conductivity.?4?In order to solve the problem of remediation of polluted low-permeability lens,the method of using weak gel in the field of oil exploitation to improve the oil exploitation rate is applied.The permeability of the background medium is reduced by the injection of weak gel to change the contrast of hydraulic conductivity of the heterogeneous formation to improve the sweep rate of the repair agent in the lens.The environmentally friendly non-toxic Polyacrylamide-aluminum citrate weak gel was chosen in this paper.During the production of weak gel,the viscosity and gelation speed of weak gel were positively correlated with the molecular weight and the reaction temperature and the concentration of polyacrylamide and the concentration of aluminum citrate crosslinker.However,if the reaction temperature is too high and the concentration of the crosslinking agent is too high,the weak gel will be excessively crosslinked and broken.Synthetic stable weak gel requires that molecular weight of HPAM is more than 15 million,concentration of HPAM is not less than 1400mg/L,reaction temperature is between 60?and80?.The low concentration of common groundwater K⁺,Na⁺,Ca²⁺,Mg²⁺cations promoted the formation of weak gel,but with the increase of concentration,it has a destructive effect on the stability of weak gel.The degree of influence of the cation on the strength of the weak gel is Ca²⁺>Mg²⁺>K⁺>Na⁺.?5?After the weak gel was injected,the permeability coefficient of the gravel medium decreased from 5.75×10^-1cm/s to 1.12×10^-44 cm/s.The contrast of hydraulic conductivity decreased from 7 to 1×10^-33 after the 600mL weak gel being injected into the gravel-coarse heterogeneous combination,and the time for the remediation agent's spread rate reaching 100%decreased from 18 hours to 5 hours.The contrast of hydraulic conductivity decreased from 13 to 2×10^-33 after the 1000mL weak gel being injected into the heterogeneous combination of gravel-medium sand,and the time for the remediation agent's spread rate reaching 100%decreased from 42 hours to 2hours.The migration rate in the lens is increased by 4 to 23 times.After the end of the remediation agent injection,the viscosity of the weak gel decreases gradually and it can be rushed out by the groundwater.Then the heterogeneous formation returns to the initial state.