Study On Oil Displacement Mechanism Of Molybdenum Disulfide Nanosheets

With the in-depth study of the exploration of oil and gas,the development of unconventional oil and gas resources has made great progress.Unconventional oil and gas resources are mainly concentrated in low-permeability,extra-low and ultra-low permeability reservoirs.The core pores of the reservoir are small and unevenly distributed,and the flow resistance of fluid in the pores is large,making it difficult to exploit.Nanomaterials are widely used in tertiary oil recovery because of their small size and high recovery efficiency.Compared with other nanomaterials,nanosheets can form surfaceto-surface contact,have higher interfacial activity and higher oil displacement efficiency.However,the understanding of its oil displacement mechanism is still unclear,so it is particularly important to carry out research on the oil displacement mechanism of nanosheets.In this paper,molybdenum disulfide nanosheets with a thickness of about 25 nm were first prepared by hydrothermal synthesis,and then modified with four surfactants to obtain modified molybdenum disulfide nanosheets.In this paper,the dispersion stability of nanosheets is characterized by measuring the change of the permeability of nanosheets dispersions with time under different salinity.The experimental results show that the dispersion stability and salt resistance of the modified nanosheets are improved.The nanosheets modified with sodium alkyl sulfate(SDS)perform the best.The oil-water interfacial tension of toluene and 0.01wt% unmodified nanosheet dispersion,and toluene and 0.01wt% modified nanosheet dispersion are measured by interfacial tensiometer.The results show that the ability of nanosheets to reduce the oil-water interfacial tension is still weak after modification.The nanosheets can spontaneously aggregate at the oil-water interface,generate a concentration gradient and form a climbing membrane under the Marangoni effect.The core flooding experiment proves that the climbing height of the climbing membrane is higher,the oil displacement efficiency is better.The ability of nanosheets to change wettability is evaluated by measuring the contact angle of glass sheets after the treatment of nanosheets.The research results show that the nanosheets modified by SDS have the strongest ability to change the wettability,which could change the contact angle of the glass sheet from 110° to 87.6°.Cyclohexane is added to 0.005wt% nanosheet dispersion and emulsification is performed to record the water separation rate of the emulsion.The results show that the modified nanosheets had an emulsification effect and the stability of the emulsion was enhanced.Lastly,through micro-flooding experiments and core-flooding experiments,it is observed that the modified nanosheets activated the remaining oil.Combined with the properties of the nanosheets,it is inferred that the nanosheets activated the remaining oil through emulsification,solubilization,wedge-shaped infiltration and change of wettability.The higher the concentration of nanosheets,the higher the climbing height of the formed climbing film,and the better the effect of enhancing oil recovery;it can still improve oil recovery at low permeability.In this paper,the performances of nanosheets are investigated by a variety of evaluation methods,combined with the comprehensive analysis of micro-flooding and core flooding experiments to reveal the oil displacement mechanism of molybdenum disulfide nanosheets,which provided guidance for the synthesis of molybdenum disulfide nanosheets for oil flooding.