Research On The Breeding And Repaired Rechnology Of Oil Drilling Cuttings Degradation Functional Bacteria

Shale gas is an unconventional natural gas produced from extremely low porosity and extracted from a rich organic dark shale formation system.It is characterized by cleanliness,high efficiency and abundant reserves.Since 2010,China has been vigorously developing the exploration work of shale gas.It has been proven that the reserve of shale gas is the world's largest,and the output is also ranked third in the world.At the same time,shale gas mining has also brought about a series of drilling waste management problems.To meet the technical needs of mining,different drilling fluids are widely used,including water-based drilling fluids,oil drilling fluid.This results in a large amount of oil-based mud and oil-containing cuttings.In face of the problem which need be solved urgently,the incineration method solidified landfill and thermal analysis method are the main techniques to deal with the drilling cuttings of oil-based mud and oil-containing cuttings.To this end,this study,from the perspective of harmless,reduced and resourced treatment of drilling waste of microbial technology for oil-containing cuttings harmless treatment.In this study,the physical and chemical properties and composition analysis of water-based cuttings and oil cuttings,in a shale gas field in southwest by China are analyzed to determine the pollutant and the pollution degree.The crude oil extracted from the oil cuttings is used to screen the microorganisms with degradation function,and the physiological,biochemical and molecular identification is carried out.Using a single environmental factor as a variable,study the degradation performance of microorganisms and obtain the best degradation conditions;Under the optimum degradation conditions,the oil drill cuttings were treated with the degrading functional bacteria to verify the degradation performance.Finally,by adding biomass materials to enhance the degradation performance of microorganisms,a small field test was conducted to investigate the feasibility of the technical means.The results of this study are as follows:(1)The water-based drill cuttings produced in the shale gas field are grayish brown mud cake after pressure filtration,while the oil drill cuttings are black after pretreatment by pyrolysis technology,giving off strong oily sludge flavor.After determination,the pH value of water-based drill cuttings is 8.47,the water content is 4.12%,the organic matter content is 3.21%,and the oil content is 2680 mg/kg;The pH value of oil cuttings is 7.94,alkaline,with water content of 6.69%,organic matter content of 5.74%,and oil content of 13,879 mg/kg.According to the "Soil environmental quality,Risk control standard for soil construction of development land",the oil content of water-based drill cuttings exceeds the risk screening value for soil contamination of development land Class I by 2.24 times;As a hazardous waste,oil content of oil-based drill cuttings is more than 2 times higher than Class II standard for risk intervention value for soil contamination of development land,which needs to be controlled strictly and proposed certain remediation measures.(2)Three strains of degrading bacteria,named ZX-2,ZX-3 and ZX-5,were finally screened from oil-based drill cuttings.The three kinds of bacteria are gram-negative bacteria.Through observation of colony morphology,physiological and biochemical identification and 16 S rDNA identification,ZX-2 and ZX-3 belong to Pseudomonas aeruginosa and ZX-5 belongs to Alcaligenes faecalis.(3)In the crude oil degradation experiment,the screened three strains of functional bacteria can degrade crude oil to the greatest extent under the conditions of 10% inoculum,pH range of 7~8 and salt concentration of 0.5%.By providing a highconcentration salt environment,the tolerance of the three strains of degrading bacteria to salt was investigated.When the salt concentration is more than 7%,the degrading bacteria can hardly survive,and certain activity can be ensured under the condition of 3% salt concentration,thus basically meeting the tolerance requirement for high salt concentration of drill cuttings.The degradation efficiency of single strain on oil-based drill cuttings for 15 days is normal,with ZX-2,ZX-3 and ZX-5 being 24.8%,37.61% and 34.58% respectively.Three strains of degrading functional bacteria were mixed equally and used to degrade oil drill cuttings under the optimal degradation conditions.After 15 days of treatment,the degradation rate reached 52.1%.(4)In order to strengthen the degradation capability of microorganisms on oil drill cuttings,the remediation process was strengthened by adding 10% by mass of cow dung organic fertilizer or decomposed sludge during the degradation of oil drill cuttings;The laboratory experiment was enlarged and the field experiment was carried out.After 126 days of treatment,the degradation rate of petroleum was 64.5% and 64.8% respectively in two groups of experiments with cow dung organic fertilizer and decomposed sludge.GC-MS was used to detect the changes of organic components in the experimental group added with cow dung organic fertilizer before and after degradation,which indicated to some extent that microorganisms utilized some organic substances such as straight-chain alkanes and aromatic hydrocarbons in drill cuttings.