Emulsion And Organic Clay Dispersion Stability In Oil-based Drilling Fluid

Oil-based drilling fluid is an emulsion system formed by oil as continuous phase,water as disperse phase.Generally,appropriate amount of emulsifier,wetting agent,lipophilic colloid and other treatment agents are needed.Compared with water-based drilling fluid,oil-based drilling fluid has strong rejection capability and high temperature-resistant ability.In complex layer,it can eliminate drill pipe sticking and protect the hydrocarbon reservoir effectively,reducing occurrence of accidents.The oil-based drilling fluid is relatively stable,less protection treatment is needed.Therefore,the oil-based drilling fluid is suitable for deep well,especially the ultra-deep wells or geothermal wells.W/O drilling fluid is an unstable thermodynamics system.Additives added in the system effect its stability.And the cutting ability of organophilic montmorillonite dissolved in paraffin oil is weak.Based on the above background,the effects of emulsifier,wetting agent,organophilic montmorillonite and other additives on emulsion stability were studied.The viscosity of paraffin oil was increased effectively by in-situ modification of sepiolite.As a result,the rheological properties of sepiolite/paraffin oil system were less influenced by high temperature.Besides,the effects of additives such as emulsifier,wetting agent and modifier on the rheological properties of organophilic montmorillonite/paraffin dispersions were also determined,providing methods to enhance cutting ability of organophilic montmorillonite in paraffin oil.The whole paper contains two sections:1.The impact of oil-based drilling fluid additives on the stability of W/O emulsion.The main function groups of the four emulsifiers were analyzed by infrared spectroscopy.Results showed that the interfacial activity of emulsifier-1 and emulsifier-2 was weaker than emulsifier-3 and emulsifier-4,which agreed with the results obtained from interface tension meter.The microstructure of the water-in-oil emulsion was observed by polarizing microscope.Interface film is denser by mixing emulsifiers containing amide and hydroxyl group with fatty acid and alkyl sulfonic acid derivatives as a co-emulsifier.And the ability of the mixed emulsifier system to reduce oil-water interface tension is stronger,leading to smaller droplet size and higher stability.Results of dynamic interface tension showed that wetting agent could adsorb on oil-water interface.However,the temperature tolerance property of emulsions containing wetting agent is weak.Besides,according to laser confocal microscopy,organophilic montmorillonite could adsorb at the oil-water interface,strengthening interface film,as a result of emulsion stability.2.The influence of oil-based drilling fluid treatment agents on the rheological properties of organophilic montmorillonite dispersion system.The physicochemical properties of the organophilic montmorillonite were characterized by thermogravimetric analysis and HAAKE rheology.It was found that the system viscosity increased at higher modified agent concentration.Sepiolite was in situ modified by quaternary ammonium salt in paraffin oil.The system viscosity increased compared with commercial organophilic montmorillonite,and the rheological properties of the viscous paraffin oil were less affected by temperature.The organophilic montmorillonite dispersion system with different treatment agents was characterized by HAAKE rheology.It was found that surfactants such as wetting agents,emulsifiers and rheological modifiers could adsorbed on the surface of organic solid particles,changing the particle interactions,thus affecting the rheological properties of the system.Branched polymer could effectively reduce the organophilic montmorillonite/paraffin oil viscosity.However,emulsifier-1,emulsifier-3,calcium dodecyl benzene sulfonate and wetting agent in the Organic Clay/paraffin oil system have thickening effects.And the combination of wetting agent and cutting agent could improve the viscosity of the system more effectively.