Research On Resource Utilization And Ecological Effects Of Spent Drilling Fluids

The development of the oil and gas industry is related to the development of the national economy and is closely related to people's lives.However,the large amount of drilling waste generated during the oil and gas extraction process,which have potential impacts on the ecological environment.How to effectively deal with the spent drilling fluids is a long-term problem faced by energy production and ecological environmental protection.This paper studies the impact of spent drilling fluids disposed in-situ(pit landfill)on the ecological environment,and analyzes vegetation restoration,crop safety,and the soil environmental quality of wellsite,and combines the indoor experiments to explore the feasibility of spent drilling fluids for land application and bioconversion,and provides a reference for the reuse of spent drilling fluids.The main conclusions were as follows:(1)The spent drilling fluids disposed in-situ improves above-ground biomass,vegetation coverage and plant height.Compared with non-mud pit,above-ground biomass in the mud pit increased by 67.01%;the vegetation coverage and plant height in the mud pit increased by 62.35%and 36.01%,respectively.The differences of heavy metals contents in plants between inside and outside of the mud pool is not significant,and their content is within the normal content range of plants.(2)The spent drilling fluids disposed in-situ increases the crop yields.Compared with non-mud pit,the average yield of maize in the mud pit increased by 24.2%,black beans increased by 29.4%,sorghum increased by 10.4%,millet increased by 14.6%,buckwheat increased by 45.2%,potato increased by 25.8%,and alfalfa increased by16.2%.The spent drilling fluids disposed in-situ does not adversely affect the quality of the crops.The heavy metal contents of crops are all within the food pollution limits,and their single factor pollution index is less than 1,and the edible part of the crops is safety(3)The heavy metal contents of the soil in the mud pool are within the soil risk screening value,and the single pollution index value is less than 1.The Nemeiro comprehensive pollution index of the soil in the mud pool is less than 0.7,the degree of contamination is safe,and the level of contamination is clean.The spent drilling fluids disposed in-situ increases the alkalinization level of the soil by increasing the p H value and electrical conductivity.The spent drilling fluids disposed in-situ significantly increases the water content of the soil profile.The average soil moisture content in the mud pit increased by 57.7%compared with that in the non-mud pit.The spent drilling fluids disposed in-situ increases the alkalinization level of the soil by increasing the p H value and electrical conductivity.(4)Spent drilling fluids can be used as a potential resource on loessal soil or aeolian soil at appropriate rate.The inhibitory effect on the growth of plant is not obvious in the two soils at the treatment with 2%spent drilling fluids.On the contrary,low application rate of spent drilling fluids(?6%)can promote the growth of plant on the red soil.Red clay improves the genetic toxicity of spent drilling fluids by inducing more micronuclei(MN)and nuclear buds(NB)in root apical meristematic cells.Due to the differences in the types of the fluids used for drilling and the type of soil that needs to be improved,the assessment of potential environmental risks of spent drilling fluids for land use cannot only consider its physical and chemical properties,but also pay attention to its biological toxicity.(5)The spent drilling fluids reduces the germination percentage and germination rate of the seeds,delays the germination time of crop seeds,and reduces the mitotic index of root tip cells.There was no adverse effect on the germination and root elongation of corn,sorghum,pea and wheat seeds when the application rate of spent drilling fluids was 1%.The spent drilling fluids induces the accumulation of H₂O₂ and O₂^·-in crops,induces the peroxidation of cell membrane lipids,and damages the cell permeability;at the same time,it increases the content of proline,soluble protein,and the activity of SOD,POD,and CAT in crop tissues.The spent drilling fluids significantly reduce the biomass of crops,especially the impact on underground biomass.When the amount of waste drilling mud is 2%,it has no adverse effects on the growth of maize,sorghum and wheat.(6)The spent drilling fluids can be converted into nutrient-rich products through bioconversion.After 6 weeks vermicomposting process,the final product has higher relative recovery efficiency of TP and TK in these initial feed mixtures with low-concentration spent drilling fluids(?30%),and their fertilizer index is higher than the recommended value for compost products(3.5).The final products have low C/N,N-NH₄⁺/N-NO₃^-ratio and humification index,indicating that it has a higher maturity and a certain agronomic potential in these initial feed mixtures with low-concentration spent drilling fluids(?30%).Low-concentration of spent drilling fluids(?30%)in the initial feed mixtures did not adversely affect the growth and reproduction of earthworms.The biomass and mortality of earthworms in these treatments were not significantly different from that in the control treatment.The results of germination index(GI),mitosis index(MI)and chromosomal abnormality rate(CA)showed that the final product containing 20%spent drilling fluids has low phytotoxicity and genetic toxicity and can be used in agriculture.