Research On Dispersion Of Nanomaterials In Brine And Their Application In Oil Well Working Fluids

With the continuous development of nanomaterials and nanotechnology,the application of nanomaterials in oil&gas exploitation filed has gotten a lot of attention.Such as nano-displacement,nano-plugging,nano-lubricants for water-based drilling fluids,and nano synergists for fracturing fluids have great application prospects.However,nanomaterials have not yet been practicely applied in oil and gas exploration.Because of the high surface energy of nanomaterials,nanoparticles are prone to agglomeration,especially in the complex environment of oil and gas fields.The application of nanomaterials in this field is mostly achieved by adding them to water-based working fluids.However,water-based working fluids are often exposed to environments with high-salt,high-temperature,and various pH,all of which can cause the sedimentation of nanoparticles.Severe agglomeration and flocculation make nanomaterials to lose positive nanoeffects,thus limiting the practical application of nanomaterials in oil and gas exploration.Therefore,the prerequisite for the application of nanomaterials in the field of oil and gas exploitation is to ensure the stable dispersion of nanomaterials in the system.Studies have shown that the most influential factors in the dispersion of nanomaterials are the electrolytes.The exisistence of electrolytes will compress the double layer on the surface of nanomaterials and weaken the electrostatic repulsion of nanomaterials in water,leading to instability of nanomaterials in aquoues.Therefore,solving the problem of stable dispersion of nanomaterials in electrolytes and high concentration electrolytes is the primary problem that should be achieved in nanomaterials in this field.In this dissertation,we propose to improve the nanomaterials through the surface modification of nanomaterials,grafting anionic polymers on the surface of nanomaterials and providing the electrostatic repulsion and steric repulsion,which makes nanomaterials stable in high concentrated electrolyte solutions.In the paper,two methods are used to graft anionic polymers onto the surface of nanomaterials.One method is to coat anionic polymers on the surface of nanomaterials(multi-walled carbon nanotubes)by free radical polymerization,and the other is to pass the surface-initiated atoms.Surface-initiated atom transfer radical polymerization(SI-ATRP)method grafts anionic polyelectrolyte brushes on the surface of nanomaterials.For the first time,anionic polymer brushes were grafted onto the nanometer surface by surface-initiated atom transfer radical polymerization SI-ATRP polymerization method to improve the stability of nanomaterials in brine.The surface modification of nanomaterials of different dimensions(nano-silica,multi-walled carbon nanotubes,graphene oxide)was realized in the article,and the anionic polymer(Poly 3-sulfonic acid propyl methacrylate potassium salt)was successfully grafted on the surface of nano-silica,multi-walled carbon nanotubes,and graphene oxide.The structure and morphology of the modified nanomaterials was characterized,and its dispersibility in salt water was further studied,as well as the stability under high temperature and alkaline conditions.The main research content is as follows:(1)The anionic polymer polystyrene sulfonate(PSS)was covalently coated on the surface of multi-walled carbon nanotubes(MWCNTs)by radical polym erization.FTIR,X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)of modified multi-walled carbon nanotubes(PSS/MWCNTs)The structure and morphology of the sample were analyzed,and the molecular weight and distribution of the polymer coated on the surface of the multi-walled carbon nanotubes were measured by gel permeation chromatography.Furthermore,surface potential analysis and particle size analysis were used to evaluate the dispersion of PSS/MWCNTs in brine.The results show that PSS/MWCNTs can stably disperse in 15 wt%sodium chloride and API brine for up to 30 days.However,stable dispersion in higher electrolyte concentrations cannot be satisfied.(2)Surface-initiated Atom Transfer Radical Polymerization(SI-ATRP)was used in this paper to successfully introduce anionic polyelectrolytes(Poly-Sulfur)on the surface of different nanomaterials(nano-silica,multi-walled carbon nanotubes,graphene oxide).Acid Propyl Methacrylate Potassium Salt)First,three different nanomaterials were surface-modified,using infrared(FTIR),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA),scanning electron microscopy(SEM),and Transmission electron microscopy(TEM)was used to analyze the structure,morphology and dispersion of the modified nanomaterials.Gel permeation chromatography was used to analyze the molecular weight of the anionic polymer chains grafted on the surface of the three nanomaterials.distributed.The results show that the modified nanomaterials obtained by this method can be stably dispersed in saturated brine and API brine.Among them,SiO2-g-SPMA can be stably dispersed for 30 days,MWCNTs-g-SPMA-2 can be stably dispersed for up to 60 days,GO-g-SPMA can be stably dispersed for up to 10 days,and some GO-g-SPMAs are stable at 30.No settlement occurred afterwards.(3)In combination with surface potential analysis and particle size analysis,the stable dispersion of three modified nanomaterials under weak alkaline conditions(pH 8-11)and high temperature was studied.The results show that the modified SiO2-g-SPMA,MWCNTs-g-SPMA-2 and GO-g-SPMA materials can all be dispersed stably in the weak alkaline(pH=8-11).The saturated brine dispersions of the three nanomaterials can stably disperse up to 24 h at 170?,and the maximum temperature for stable dispersion in API brine is 80?.(4)Ultra-low permeability mud cakes were successfully prepared in this paper,and the average permeability of mud cakes obtained was 4.69×10-4 mD.The three nanomaterials modified by SI-ATRP method above were used as nano-plugging agent.The structure shows that all three nano-materials effectively plugged the pores and decreased permeability of mud cakes.With 0.5 wt%SiO2-g-SPMA,reduction rate of permeability was about 78.25%;And 0.3 wt%MWCNTs-g-SPMA-2 was added,reduction rate of permeability was about 50.96%;with 0.3 wt%GO-g-SPMA,reduction rate of permeability was 45.42%.After mixing 0.1 wt%SiO2-g-SPMA and 0.1 wt%GO-g-SPMA,reduction rate of permeability Kr(%)increased to 83.58%.Finally,the micro-morphologies of the mud cake with the plugging agent and without the plugging agent were investigated.It was observed that most of the micro-sacle and nano-sacle pores were effectively plugged,the smaller size of nano-plugging agent could pass through the throat of mud and exsite in filtrate.By the micromorphology analysis,the above three nanomaterials can be observed in the filtrate,that further demonstrated the stable dispersion of the modified nanomaterials in the system and effectively blocking micro and nanoscale pores.