Study On Innocuous Treatment Technology Of Oil Cuttings In Diesel-based Drilling Fluid

Diesel-based drilling fluid has been widely used in drilling,because of its good lubricity,wellbore stability and little damage to oil and gas reservoirs.However,there is a large amount of aged diesel oil in the oil drilling cuttings,which is difficult to degrade in the natural environment and harmful to the environment.Recycling this part of diesel is not only reduce environmental pollution,but also reuse the base oil.In this paper,combined with existing drilling cuttings treatment methods,the combination of solvent leaching and microbial treatment was optimized to deal with oil cuttings.Diesel oil was recovered by the leaching method,and diesel oil that was difficult to be recovered was degraded by microorganisms.After co-processing,oil cuttings can be treated harmlessly and as resources.The diesel-based drilling fluid oily cuttings from Sichuan shale gas wells were taken as the research object,which were difficult to treatment,because of 10.97%oil content,small particle size and complex components.A kind of efficient leaching agent was developed through leaching experiment,and the mixture ratio of each solvent was n-heptane:methyl acetate:petroleum ether=5.7:3.8:0.5.Through calculation,the Hansen solubility parameter of composite solvent was close to petroleum pollutants.Through single factor optimization experiments,the optimal conditions for leaching experiment were determined as follows:solid-liquid ratio of 1:5,stirring rate of 400 r·min^-1,leaching time of 20 min.At room temperature,the removal rate of petroleum pollutants in drilling cuttings reached 68.97%.After distillation,leaching agent recovery rate was 87%and properties of recovered composite solvent remain unchanged,which can be recycled for many times.The performance of recovered diesel reached the National III standard and can be used to prepare oil-based drilling fluids to realize resource utilization.After solvent leaching treatment,there was still part of diesel oil in that was difficult to recover,and oily cuttings cannot meet the national secondary emission standards.Therefore,oily cuttings were further treated by microbial degradation method.Five biodegrading bacteria with 0#diesel oil as only carbon source were isolated from oily cuttings.The dominant strain W2 was identified by studying degradation ability of bacteria.The physiological&biochemical characteristics and molecular identification showed that strain W2 was bacillus lichoriformis.Through single factor shaker culture experiments,the optimal growth conditions of strain were determined:the inoculation amount of 5%was inoculated in inorganic salt medium with（NH₄）₂SO₄ as nitrogen source,K₂HPO₄ as phosphorus source,p H 7.0,and placed in shaking table at 37℃for 6 days.After solvent leaching and microbial degradation,the oil content of drill cuttings decreased to 0.47%.The surface tension of strain W2 decreased from 70.1 m N·m^-1 to 29.7 m N·m^-1 in fermentation broth,which indicated that strain W2 exerted its ability to degrade diesel oil by producing surface active substances.These surface active substance produced by strain W2 was purified and qualitatively analyzed by extraction and TLC.Results showed that surface active substance was glycolipid surfactant and yield was 1.49 g·L^-1 after 2days under optimal growth conditions.After co-processing of solvent leaching and microbial degradation,oil content of drill cuttings decreased from 10.97%to 0.47%,which reached the direct discharge standard.Moreover,the drill cuttings leaching solution was clear,with extremely low chroma and turbidity,and the content of other heavy metal ions were also lower than the national secondary standard,showing good environmental performance.