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Excessive torque on tool surfaces resulting in friction and wear in the process of well drilling remains a big challenge for the oil and gas exploration industry. In this study, two kinds of glycerides are encapsulated and serve as lubrication additives to improve the tribological properties of water-based drilling mud. It is found that encapsulation improved the thermal stability of microcapsules. In addition, tribological experiments were carried out using a ball-on-disc tribometer. Results revealed that glyceryl monostearate (GMS)-filled microcapsules largely improved the tribological properties of drilling mud compared to empty microcapsules and glyceryl tristearate (GTS)-filled microcapsules and contributed a protective film on the worn surface formed by released lubricants. However, increasing the amount of lubricant additives failed to further improve the friction reduction performance. Moreover, a remarkable decrease in damage and wear cracks indicated excellent antiwear properties of GMS-filled microcapsules. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the tribology behavior of steel–steel contact under the lubrication of water-based drilling mud with different oleic acid-filled microcapsules as lubricant additives. Design/methodology/approach: A ball-on-disc tribometer was used to evaluate the lubrication properties of the steel–steel contact. The wear tracks of the worn surfaces were observed by a scanning electron microscope. Findings: Results show that the dependence of both friction and wear on the category of additives shares a consistent pattern. In contrast to oleic acid and empty microcapsules, oleic acid-filled microcapsules achieve the best tribological performance which is related to the lubricant effect of oleic acid and the isolation and rolling abilities of microcapsules. Practical implications: This study provides a helpful method of encapsulated lubricant additives to prolong lubrication performance for steel–steel contact. Originality/value: This study has applied microcapsules to improve the tribological properties of drilling mud. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0320/ [ABSTRACT FROM AUTHOR]

Lubrication properties of drilling mud determine the performance of drilling operations. In this research, five imidazolium cation–based and two phosphonium cation–based ionic liquids (ILs) were studied as additives to evaluate the lubrication performance of water-based drilling mud. Results show that ILs remarkably improve the lubricating properties of drilling mud, which is ascribed to the tribofilm formation on the rubbing surface. The friction coefficient of ILs highly depends on viscosity due to interfriction forces of the bentonite on the worn surface and adsorption of ILs in bentonites, consequently limiting the formation of a protective film. In addition, worn surfaces with several cracks and crushed particles were observed by scanning electron microscopy (SEM) micrographs, indicating that microcutting and three-body abrasive wear are dominant. [ABSTRACT FROM AUTHOR]

Film-forming properties of polymer in aqueous solution flowing through a nanogap have been investigated by using a thin film interferometry. The film properties of linear polymer in aqueous solution flowing through a confined nanogap depend on the ratio of water film thickness to averaged radius of polymer chains H0/RPolymer. It was found that the lubrication film thickness of linear polymer in aqueous solution decreases as the polymer molecular weight increasing when H0/RPolymer < 2 ∼ 3. A new lubrication map was proposed, which includes the lubrication regime of weak confinement influence, the lubrication regime of strong confinement influence (LRSCI), and the transition regime of confinement influence. It is very difficult to increase the lubrication film thickness using the higher molecule weight in the LRSCI regime. The lubrication mechanism inferred from our experimental results may help to better understand the dynamic film properties of linear polymer in aqueous solution flowing through a nanogap. [ABSTRACT FROM AUTHOR]

The influence of surface hydrophilicity on adsorbed water layer was investigated using a thin film interferometry and a microtribometer based on laser interferometers. Experimental results indicate that, in the mixed film lubrication from the boundary lubrication to the thin film lubrication, the hydrophilic surface promotes the forming of thinner water film and the higher friction. It is thought that a layer of water adjacent to the surface forms an ordered water layer whose characteristic determines the properties of adsorbed water layer in the contact area. [ABSTRACT FROM AUTHOR]

Abstract The tribological performances of proppant particle-shale rock contact determine the quality of hydraulic fracturing. In this work, the tribological property of quartz sand particle-shale rock contact was investigated. The friction of the contact is highly affected by lubricating media at the interface and water saturation state of the particles and the shale rock, which is related to water as a lubricant for the contact and sand particles softened by absorbing water, respectively. Under lubrication by guar gum aqueous solution, the friction of the contact was found to change with guar gum concentration while normal load and sliding speed exhibited little influence. Highlights • The friction of the contact is dependent on lubricating media at the interface. • The friction of the contact is related to water saturation state of samples. • The friction of the contact was found to change with guar gum concentration. • The friction of the contact is hardly affected by normal load and sliding speed. • The wear mechanism of shale rock is determined by guar gum concentration. [ABSTRACT FROM AUTHOR]

Over the past decades, hydraulic fracturing has been adopted extensively in the petroleum field to stimulate the growth of shale gas production. To better understand hydraulic fracturing, the frictional behavior of shale rock-silica contacts was investigated. Data from experiments show that friction coefficient of the contact gradually increases from 0.2 to somewhere in the range of 0.3–0.4, and then reaches steady state with increasing load, which is directly related to the transformation from the mixed to the boundary lubrication regime of guar gum aqueous solutions. Moreover, the friction coefficient of the contact has no trend with the increasing concentration of guar gum aqueous solution, which is attributed to rheological performances of guar gum in contacts. [ABSTRACT FROM AUTHOR]

In this study, a direct observation of the dynamic behaviors of wax-in-oil flow at the rough soft contact was conducted using the optical fluorescent technique. A contact area was produced between a sliding rigid glass plate and a stationary polyurethane elastomer ball. A mixture of wax in oil was used with 90 % silicon oil and 10 % paraffin wax by weight content. It was found that wax particles played an important role at the rough soft contact, which includes the accumulating process from the inlet region of the contact area and passes through at the central region. The behavior of the entrapped wax particles depends on the soft lubrication. Experimental results show that when the speed of sliding friction has a small value, the accumulation and passing through processes of wax particles occur more slowly at the soft contact interface. A major change occurs in the scratch-like lines when the sliding speed increases with rapid change of the conformity between the sliding soft surfaces. [ABSTRACT FROM AUTHOR]

A microbubble phenomenon induced by micro-oscillation in the grease lubricating film confined within a nanogap between a highly polished steel ball and a smooth glass disc has been observed with an interferometer. Experimental results show that when the micro-oscillation frequency is a constant value, the microbubble number increases with the micro-oscillation amplitude. When the micro-oscillation amplitude is a constant value, the microbubble number increases with the micro-oscillation frequency when the latter is lower than the critical value and decreases with the micro-oscillation frequency when it is higher than the critical value. Theoretical models and analyses have been used to discuss the bubble formation and describe the characteristics of bubble movement. [ABSTRACT FROM AUTHOR]

Aqueous lubrication is commonly regarded as friendly to the environment. We review current knowledge of the behaviors and mechanisms of aqueous lubrication. Major methods for investigating aqueous lubrication are addressed. We describe studies on both friction and film formation performance of various water-based lubricants. Additionally, we discuss possible underlying mechanisms of aqueous lubrication. Attention is also drawn to continuing topics of investigation and some unsolved problems. [ABSTRACT FROM AUTHOR]

Lubrication failure of polyalphaolefin (PAO) oil film at high slide/roll ratios of more than 1.9 has been experimentally investigated based on a ball-on-disc configuration. The central film thickness and the oil pool shape in the contact were determined by optical interferometry and fluorescence microscopy, respectively, and the traction coefficient and surface profiles of the tribopairs were measured using a tension-compression sensor and light surface profilometer, respectively. The results demonstrate that the central film in the contact was in the elastohydrodynamic lubrication regime at the initial stage under high slide/roll ratios. Variation in the traction coefficient and the presence of wear scars on the disc surface shows that the sliding speed played an important role in lubrication failure. We propose that a thermal effect explains the obtained results at high slide/roll ratios. The fluorescence technique combined with optical interferometry was also used to gain more understanding of lubrication properties under mixed slide/roll conditions. [ABSTRACT FROM AUTHOR]

Abstract: The tribological properties of three different films commonly used in microelectromechanical systems (MEMS) under the lubrication of ionic liquid (IL)/water mixtures with various concentrations in the running-in process have been investigated. Results show that coefficients of friction (COFs) and wear rates for low temperature silicon oxide (LTO)/Si3N4 vary in a similar way to the ones for poly-Si/Si3N4 under the lubrications of different IL/water mixtures. In contrast, the differences in COFs and wear rates are more significant in that the COFs and wear rates increase dramatically with the decrease in IL/water concentration in the case of self-mated Si3N4, while the differences in COFs and wear rates for the two other tribopairs are relatively small when the concentration is changed. The period of the running-in process reduces with the increase in IL/water concentration for all the tribopairs. Effective hydrodynamic lubrication can be found in the case of Si3N4/Si3N4 tribopair at higher IL/water concentrations without an evident running-in process, however, such a phenomenon cannot be observed for the other two tribopairs. Different wear mechanisms will also be analyzed in this paper. [Copyright &y& Elsevier]

Abstract: Relative optical intensity interference was used to measure the lubrication film thickness when four kinds of polyalphaolefin (PAO) were used as lubricants confined between a smooth sapphire disc surface and a rough steel ball surface. Maximum Hertz contact pressure up to 3GPa was applied in the central part of the contact region in mixed lubrication. It was found that the contact ratio (the ratio of real contact region to the whole nominal contact region) is related to the film thickness, the applied pressure, the surface roughness and the rolling speed, and so on. Contact ratio evidently reduces as lubrication film thickness or rolling speed increases. Quantitative relationship between the contact ratio and the influence factors was summarized based on the nonlinear fitting of experimental measurements. A formula was put forward to calculate the contact ratio at high pressure conditions according to the current experimental results. [Copyright &y& Elsevier]

Abstract: The oil-in-water emulsion has been widely used as lubricant in metal working such as metal rolling and cutting. The film formation ability of emulsion was considered as an important evaluation factor. Thus the film formation mechanism and characteristics of emulsion have been widely investigated. However, the mechanism is still dubious and film forming characteristics were seldom discussed under an oil volume percentage of 0.05%. In this paper, a lubricating film testing apparatus is used to investigate the film forming characteristics of oil-in-water emulsion between the surface of a steel ball and that of a glass disc coated with chromium. By carrying out experiments under extremely low oil volume percentages (0.005–2.5%), some new phenomena are found in our program. The film formation mechanism of oil-in-water emulsion is discussed based on the different film forming performances of emulsion with different oil volume percentages. New viewpoints on the film formation of emulsion are put forward in this paper. [Copyright &y& Elsevier]