Study On The Influence Of Typical Organic Pollutants In In-situ Oil Shale Exploitation By SCW On Ground Water Environment

The super-critical water method has the advantages of low process temperature,high overall oil yield,and economical greenness in the process of in-situ oil shale exploitation.There is still a lack of a large number of experimental studies and in-depth discussions on what impact it will have on the groundwater environment.Therefore,the study of the impact of typical organic pollutants in the in-situ mining of oil shale by the super-critical water method on the groundwater environment can be used for the subsequent prevention and control of groundwater environmental pollution and the site.Repair and provide guidance.This paper relies on the projects of the National Natural Science Foundation of China"Research on the Impact of Oil Shale In-Situ Mining on Groundwater Environment（41572216）"and"Research on the Mechanism of BTEX Release and Contaminated Aquifer During Oil Shale In-Situ Mining（20100331）",with Huadian Shale was taken as the research object.Using the super-critical water method in-situ mining technology（SCW method）to carry out experiments on the impact of super-critical water method in-situ mining oil shale on the underground environment,and compared and analyzed the output gas and oil shale under different experimental conditions.Residue mineral composition,functional group composition and pore changes,to find out the impact of the process of in-situ mining of oil shale super critical water on the physical and chemical and hydraulic properties of oil shale formations,and to reveal the impact of this technology on changes in the underground environment.The research on the impact of typical organic pollutants in oil shale on the groundwater environment by in-situ mining method has laid a foundation.Collect super-critical wastewater samples after in-situ mining of oil shale by super-critical water method at335°C,350°C,and 385°C to analyze the p H value,TOC value,typical organic pollutants（benzene series,nitrobenzene,polycyclic Aromatics-naphthalene,phenol）concentration,find out the release law of typical organic pollutants in the groundwater environment,use the reaction kinetic equation to fit and reveal the release process,use16S r RNA technology to measure the concentration of organic matter and aromatic hydrocarbons with high concentration The structure of microbial flora in super-critical wastewater reveals the response characteristics of microorganisms to the remediation of typical organic matter-contaminated groundwater environment after in-situ oil shale mining by super-critical water method.Select oil shale residue samples at 335°C,350°C,and 385°C corresponding to three different oil production rates of oil shale,and carry out experimental research on the constant temperature release of residues in the groundwater environment after in-situ mining of oil shale,and analyze the residues In the groundwater environment,the released p H value and the change law of the concentration of typical organic pollutants,using the release kinetic equation to fit and reveal the release characteristics,to find out the pollution of the oil shale residue after the in-situ mining of oil shale to the groundwater environment properties and long-term effects.16S r RNA sequencing was used to identify the characteristics and structural composition of the microbial flora in the released fluid,which provided a scientific basis for the remediation of groundwater environmental pollution after in-situ mining of oil shale.On the basis of the high oil yield of oil shale with catalyst added,in-situ oil shale exploitation experiment with super-critical water method with added catalyst CaCl₂ was carried out to find out the change rule of p H value and concentration of typical organic pollutants in the super-critical wastewater with added catalyst CaCl₂,to analyze the catalytic mechanism of catalyst CaCl₂ on the in-situ recovery of oil shale by super-critical water method.Using the TMVOC module of TOUGH 2.0 software,combined with the laboratory experimental data of in-situ oil shale extraction by the above-mentioned super-critical water method and the field data of the pilot demonstration project of in-situ oil shale extraction in Jilin University,and according to typical organic pollutants（benzene,PAHs-naphthalene）,three groundwater environment simulation scenarios with natural attenuation conditions,enhanced microbial degradation rate of 1 times,and enhanced microbial degradation rate of 2 times were set respectively,and numerical simulation work was carried out for the engineering application of oil shale in-situ exploitation of super-critical water,to analyze the impact of microorganisms on the groundwater environment under different simulation scenarios.The main conclusions obtained in this paper are as follows:（1）The effect of in-situ mining of super-critical water-oil shale on underground environmentThrough the in-situ oil shale exploitation experiment of super-critical water method under different conditions,combined with microscopic detection technology,the composition of the generated gas and the change characteristics of the physical,chemical and hydraulic properties of the oil shale were ascertained.The gases produced in the experiment are mainly methane,carbon dioxide,hydrogen,hydrogen sulfide and carbon monoxide.The content of methane,hydrogen and carbon dioxide increased significantly with the increase of temperature,but the content of carbon monoxide and hydrogen sulfide did not change significantly.Combined use of XRD,FT-IR,and BET microscopic detection techniques,the results show that feldspar in the residue mineral composition increased,pyrite decreased,kerogen C=C stretching disappeared,and a large amount of organic matter remained in the residue,and the specific surface area increased from 7.63 m²/g to It rises to 30.09m²/g,mainly with mesopores,indicating that the super-critical water method has a certain impact on the physical,chemical and hydraulic properties of oil shale.（2）Release characteristics of organic compounds in SCW wastewaterThrough in-situ mining oil shale experiments with super-critical water under different conditions,the p H value and release characteristics of organic matter in super-critical wastewater were ascertained,combined with molecular biological detection technology,the response characteristics of microbial flora were revealed.Under different experimental conditions,the p H value of the super-critical wastewater was neutral to acidic,and the TOC value,benzene series,nitrobenzene,and polycyclic aromatic hydrocarbons-naphthalene concentrations continued to increase with the extension of the experiment time,and the release of organic matter conformed to the pseudo-second-order kinetic model.The chemical reaction is mainly accompanied by ion exchange process.Due to the stable chemical structure of phenol,the concentration change is not obvious.Under different experimental conditions,the dominant bacterial groups in super-critical wastewater were petroleum hydrocarbon degraders and polycyclic aromatic hydrocarbon degraders,indicating that there are microbial degradative bacteria that can use organic pollutants as nutrient substrates in the environment.（3）Constant temperature release experiment of oil shale residue after in-situ miningThrough the constant temperature release experiment of the residue after in-situ mining by the super-critical water method,the p H value of the release liquid and the release characteristics of organic pollutants were found out,combined with molecular biological detection technology,the response characteristics of the microbial flora were revealed.The p H value of the oil shale raw rock release fluid increased to 10.15 and then showed a downward trend,and the concentration of organic pollutants released during the entire release period was small.In the residue release liquid,the p H value,benzene series,and nitrobenzene concentration decreased with time,and the concentration of polycyclic aromatic hydrocarbons-naphthalene increased exponentially.The genera are dominated by Burkholderia,Ralstonia,and Flavobacterium,accounting for 10.74%,9.62,and 9.15%respectively,indicating that there are efficient degrading bacteria that can degrade organic pollutants in the residue release liquid.（4）Release characteristics of typical organic pollutants in SCW wastewater with catalyst additionDetermine CaCl₂ as a catalyst,carry out in-situ oil shale mining experiment with super-critical water method with added catalyst,find out the release characteristics of typical organic pollutants in super-critical wastewater,and analyze the catalytic mechanism of CaCl₂ and its impact on groundwater environment.With the prolongation of heating time,the p H value of the wastewater is strongly acidic,and the release concentration of benzene series,nitrobenzene,and polycyclic aromatic hydrocarbons-naphthalene is suppressed.Calcium oxide is generated by decomposition,which changes the bond force of kerogen structure inside the oil shale and inhibits the formation of aromatic compounds.With the increase of CaCl₂ addition,the concentration of phenol increases gradually.It shows that the super-critical wastewater added with catalyst poses a certain threat to the groundwater environment.（5）Research on simulation of groundwater environment in in-situ mining of oil shale by super-critical water methodThrough laboratory experiments and field tests,combined with the natural attenuation characteristics of organic pollutants,the simulation scenarios of groundwater environment with different microbial remediation effects are determined,combined with numerical simulation methods,it is revealed that on the basis of microbial remediation,the in-situ mining of oil shale by the super-critical water method has a significant impact on the environment.Long-term effects on the groundwater environment.Under different simulation scenarios,the maximum pollution plume diffusion range of benzene and PAH-naphthalene can be reduced by 50%and 49%.The innovations of this paper are as follows:（1）Revealed the release characteristics and rules of typical organic pollutants in super-critical wastewater and oil shale residues at different mining temperatures and different mining times in the process of in-situ oil shale extraction by the super-critical water method,through the reaction kinetic equation of the release processthe fitting of,revealed the release mechanism of typical organic pollutants in the groundwater environment.（2）Analyzed the characteristics of microbial flora in super-critical wastewater and residue release fluid,found the dominant flora at the phylum level during the high temperature and high pressure experiment of oil shale,and revealed the degradation efficiency of microbial flora to typical organic pollutants and impact on the groundwater environment.（3）Fully considering the degradation of microorganisms,the TMVOC module in TOUGH 2.0 was used to construct a simulation model for the migration,transformation and degradation of organic pollutants in the groundwater environment,simulating the migration path and diffusion range of organic pollutants and the degradation law of organic pollutants by microorganisms,put forward the key technical points of the enhanced degradation type natural decay method.