Tribological And Mechanism Research Of Series Lubrication Additives In Water-based Mud

Nowadays,with the rapid development of China’s economy,the demand for oil and gas resources has been risen sharply.The design of environmentally friendly and efficient drilling fluid is of great significant to increase oil and gas development and enhance exploration efficiency.The application of traditional water-based lubricant additives in the field of oil drilling has many limitations,and the understanding of the basic theory of the effect of lubricating additives in water-based mud conditions need to be improved.Aiming at these problems,this paper studied the tribological properties and mechanisms of water-based lubricant additives under steel-steel friction.The main conclusions of this paper are as follows:（1）Using fatty acid glycerides as lubricating additives for water-based mud,the effect of fatty acid structure and concentration of glycerides on the tribological properties of water-based mud under steel-steel friction pair were studied.It was found that fatty acid glycerides with longer alkane molecular chain（carbon chain length of 18）,unsaturation,and more hydroxyl（monoglycerides）were beneficial to the lubricating effect of water-based mud,and the main wear mechanism was abrasive wear caused by bentonite particles.（2）Ionic liquids were selected as the lubricating additives for water-based mud.The effect of type of the anions,concentration,and applied load on the tribological properties of water-based mud were studied.It was found that the friction reduction of ionic liquid was attributed to the formation of absorption film and tribofilm on the steel surface.In addition,[OMIM]Br had better friction reduction and anti-wear effect at high concentrations;the effect of types of anions（BF₄^-,NTf₂^-,Ibu^-,and PF₆^-）had little effect on the lubrication performance,and the main wear mechanism was fatigue wear.（3）Glycerides and ionic liquids were designed to encapsulated in the microcapsule shell material.The functional groups,particle size distribution,thermal weight loss,and physicochemical properties of glyceride filled microcapsules were confirmed by FTIR,DLS,TGA,and APT methods.The effect of concentrations and applied load of microcapsules on the tribological properties of water-based mud were studied.It was found that the friction reduction and anti-wear effects of glyceride microcapsules were decreased first and then increased with the increasing concentration;the friction reduction and anti-wear effects of[OMIM]Br microcapsules were better than that of[OMIM]BF₄microcapsules;additionally,microcapsules had different responses under different stress.（4）To further understand the friction reduction and anti-wear properties of microcapsules,the oleic acid and self-emulsifying ester were designed to encapsulated in the shell material of the microcapsules.The effect of concentration and size on the tribological properties of the water-based mud were studied.It was found that the coefficient of friction（COF）decreased from 0.16 to 0.06 under the lubrication of high concentration（8 wt%）oleic acid microcapsules,decreased by 62.5%;the effect of different sizes of microcapsules on the friction reduction effect was small,and the main wear mechanism was abrasive wear.The self-emulsifying ester microcapsules with small size（0.4μm）had strong bearing capacity under load,and the friction coefficient decreased from 0.058 to 0.046,decreased by 18.1%.The main wear mechanisms were adhesive wear and abrasive wear.（5）The change of friction reduction and anti-wear effects of different types of water-based lubricant additives were summarized,and it was found that there was a positive correlation between the friction reduction and anti-wear properties of microcapsules:COF=0.00185WSD-0.146.Glyceride filled microcapsules had the optimal friction reduction and anti-wear properties,with the friction coefficient distributed between 0.05-0.19,and the wear scar diameter distributed between 101-109μm.