CO₂ Stimulating Switching Solvent Treatment Oil-Based Drilling Cutting Technology Research

Shale gas(oil)mining industry releases a large amount of oil-based drilling cuttings every year,which brings harm to ecosystem and environment,Therefore,it is urgent to develop an environmental friendly and efficient technology to deal with the oil-based drilling cuttings that are not up to the standard.This paper analyzes the present situation and problems of oil-based drilling cuttings treatment technology at home and abroad,and puts forward that N,N-Dimethylaminoethyl,a CO₂ stimulated switching solvent,can be used for oil recovery and treatment of oil-based drilling cuttings.The research work has been carried out in the aspects of optimization of CO₂ switching solvent,process optimization of oil removal device,reaction mechanism of treating oil-based drilling cuttings with switching solvent,process analysis of oil removal device and design of pilot plant.According to the analysis of the properties of oil-based drilling cuttings,the oil content of the samples is up to 16.54wt%,and 11 heavy metals such as Ba,Ti,Sr,Pb and Ni are detected.N,N-Dimethylaminoethyl ester was selected as the research object in the market organic amine CO₂ switching solvent combined with the factors of oil removal effect and technical and economic cost.The process of removing oil from oil-based cuttings by N,N-Dimethylaminoethyl mainly consists of three unit processes:solvent extraction,protonation reaction and deprotonation reaction.In the extraction process,the best material mass ratio is oil-based drilling cuttings:switching solvent:water=4:2:1;the order of feeding is that oil-based drilling cuttings are fully mixed with switching solvent,and then water is added;the best mixing conditions are rotation speed of 400r/min,time of20min and reaction temperature of 50?.In the process of protonation,the flux of CO₂ is 3L/min·L^-1,and the solvent can be protonated completely in 25min at room temperature,and the recovered oil can be obtained.In the process of deprotonation,the flux of N₂(air)is 3L/min·L^-1,the reaction temperature is 50?and the effect of deprotonation is the best.It can remove CO₂ and recover solvent quickly and efficiently.The surface wettability of oil-based drilling cuttings and extracted residue was analyzed.The average time of water drop penetration decreased from 138s before extraction to 24s after extraction,and the hydrophilicity was significantly enhanced.The results of surface element analysis showed that the content of C and S elements on the surface of the residue decreased,while the content of Si element increased relatively,which confirmed that the increase of wettability of the surface of drilling cuttings was caused by the separation of organic matter from the surface of drilling cuttings,and revealed the mechanism of solvent extraction of petroleum.Under the optimum process parameters,the oil content of the oil-based cuttings with oil content of 16.54%was reduced to 1.70%,and the recovery of petroleum and switching solvents were 90.12%and 90.15%,respectively.FT-IR analysis showed that the structure of the recovered oil and the recovered switching solvent remained unchanged.The results show that the recovery of petroleum is84.24%-95.28%and the oil content of solid-phase residue is less than 5%,which proves the universality of the process.Based on the results of process analysis,the test process is designed and the equipment is selected.The test process consists of a solid-liquid extraction unit(mixing agitator),an oil-water separation unit(horizontal screw centrifuge),an extraction oil separation unit(loop reactor)and a switching solvent recovery unit(dissolved air flotation machine).