Research On Evaluation Methods Of Land-based Utilization Of Low-oil Solids

In the process of oil and gas field exploitation,pollutants,including drilling debris,base oil,oily sludge,was processed with polysis,thermochemical cleaning,chemical extraction and other methods.However,after treatment,the pollutants contaminated with lower petroleum hydrocarbons are not yet been clearly defined in the landification.An evaluation of the petroleum-containing solids collected from Changning shale gas field in Sichuan and Liaohe oil field in Liaoning was constructed in this paper.The Principal Component Analysis(PCA)was applied to screen out the main evaluation indicators,and a combination of Analytic Hierarchy Process(AHP)and the Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)was applied,combined with Triangular fuzzy numbers(TFNs)and Simple additive weighting(SAW),followed a sensitivity analysis and experiment to verify the accuracy and precision.According to these,weighted of the petroleum-containing solid matters was calculated.At the same time,the petroleum-containing solid was used in indoor experimental research,and the landification of the solid was explored by investigating the growth of plants,the petroleum dissipation and the soil microbial propagation.(1)According to PCA,five indicators,including temperature,light intensity,water content,petroleum hydrocarbons and soil organic matter,was set as effective indicators.And an evaluation system with three-criteria and nine-index was established for the petroleum-containing solids.The criteria layer includes the physiological characteristics of plants(BI),natural conditions(B2)and soil environmental factors(B3).Among them,the physiological characteristics of plants are mainly plant survical rate(C1),germination rate(C2),growth rate(C3)and biomass(C4);natural conditions mainly include light intensity(C5),moisture(C6)and temperature(C7);soil environmental factors mainly refer to soil petroleum pollutant content(C8)and soil fertility(C9).(2)It was moisture(C6)and light intensity(C5)that accounted for a great weight for petroleum-containing solid in Changning shale gas field.And after sorting the indigenous plants,Alternanthera philoxeroides and tall fescue showed great potential.Under comprehensive conditions,the experiment shows that the evaluation system is feasible.The parameters of each index shown that the plants can grow better under 40%moisture,20?,60%(570-70?mol/m2/s)light intensity,and when in 1.0%contaminated soil,the petroleum dissipation can be the highest.After weighted calculation,the evaluation indexes of petroleum-containing solid in Changning shale gas field is 0.4601,andwas at the third level of the evaluation grade and belong to the category of mild influence.(3)It was moisture(C6)and temperature(C7)that accounted for a large weight,nearly 16%and 29%,in the evaluaton system for petroleum-containing solid collected from Liaohe oil field.And after ranking,tall fescue showed a higher score for the evaluation.By calculating the sensitivity coefficient of each index,it indicated that the evaluation system is feasible.The optium parameters of each index was found to be 40%moisture content,30?,and 60%(570-700?mol/m2/s)light intensity,and it can be great for plant growth and petroleum dissipation with the pollution concentration was 2.0%and 2.5%.According to the weights calculation,the evaluation index of the petroleum-containing solid in Liaohe oil field is 0.6426,it was at level 4 of the evaluation level and belongs to the category of moderate impact.(4)The plants selected from the evaluation system were combined with petroleum-degrading bacteria for the study of landification of low-oil solids in Changning,Sichuan.The results showed that the removal efficiency of petroleum hydrocarbon pollutants in soil was up to 61.3%,and the biomass of above-ground and underground parts of plants was 2.8 times and 1.6 times than treatment of plant solely.The addition of petroleum degrading bacteria can greatly promote the growth of soil microbial quantity,and the soil dehydrogenase activity and fluorescein diacetate activity increase in the first 30 days.At 120 days,a stable microbial community can be formed in the oil-containing solid phase,with Alphaproteobacteria and Gammproterobacteria as the main components.Therefore,this method can be used as an effective and feasible approach for land-based utilization of contaminated soil in shale gas production wells in the region,but it should also be considered that the competition between plants and microorganisms,indigenous bacteria and microorganisms,thus,the regular addition of bacteria canacquire long-term removal of petroleum hydrocarbon pollutants and improve soil structure.