Effects of sliding speed on the tribological behavior of AA 7075 petroleum casing in simulated drilling environment

https://doi.org/10.1016/j.triboint.2020.106194Get rights and content

Highlights

  • Effects of sliding speed on tribological behavior of AA 7075 oil casing are presented.

  • Best wear resistance of AA 7075 was observed at sliding speed of 0.314 m/s.

  • The performance of tribo oxides layers is the key point of wear mechanism transition.

  • Tribo oxides layer are formed and removed rapidly at a higher sliding speed.

Abstract

This work investigated the effects of sliding speed on tribological behavior of AA 7075 petroleum casing in simulated drilling environment by pin-on-disc wear test. The main wear mechanism of AA 7075 disc at low sliding speed (0.0628 m/s and 0.157 m/s) was abrasive wear and oxidative wear at middle sliding speed (0.314 m/s). As sliding speed increases to higher sliding speed (0.471 m/s and 0.628 m/s), adhesive delamination wear dominated the wear process. The tribo oxides layer can efficiently protected the alloy substrate only at sliding speed of 0.314 m/s. At higher sliding speeds, tribo oxides layer were removed quickly once it was formed due to its internal fractures of tribo oxides and lower bonging strength with substrate.

Introduction

As energy demand increases, drilling operation in petroleum industry is extended into more-hostile environments, such as extra deep reservoirs with HTHP (high temperature and high pressure) [1], acid reservoirs which contain H2S and CO2 [2] and complex reservoirs which are buried in geological fault [3]. Drilling into these reservoirs, conventional casing materials such as N80 steel can no longer meet the requirements of corrosion and fatigue resistance [4,5]. Besides, the increased casing weight with well depth brings huge construction difficulty [6]. Due to the exceptional strength-to-weight ratio [7], excellent fatigue performance [8] and corrosion resistance [9], AA (aluminum alloys) 7075 was used as material for petroleum casing manufacturing recent years [10,11]. However, it has also been reported that the wear rate of light alloy tends to be higher than steel for the same tribological conditions [12]. The wear of AA 7075 casing induced by its contact with harder drill string (steel) is still non-negligible in oil and gas field application [13].

Recent years, wear behaviors of AA 7075 has been extensively studied under different conditions by many scholars. Lu et al. investigated the influence of temperature on friction behavior of AA 7075 by ball-on-plate sliding test and found that ploughing friction is the main wear mechanism at temperature below 150 °C while adhesive peeling off dominates plate surfaces when higher than 300 °C [14]. Shen et al. conducted a series of dual-rotary fretting wear tests of AA 7075 alloy in oil and water. Results showed that abrasive wear, delamination and oxidative wear dominated the wear process in water, while abrasive wear took the lead in oil [15]. Avcu investigated the wear behaviour of ECAP (Equal channel angular pressing) processed AA 7075 and pointed out that the COF (coefficient of friction) and wear rate of the AA7075 alloy increased with ECAP despite of the increased hardness [16]. Venkataraman and Sundararajan carried out pin-on-disc wear tests to study the relationship between the mechanically mixed layer (MML) and tribological performance of AA 7075. It was concluded that the presence of a stable MML provided the best wear resistance despite of the increased friction coefficient [17]. Baradeswaran et al. evaluated the effect of graphite particulates on the friction and wear behavior of AA 7075 through pin-on-disc wear tests under dry sliding condition. They found that the significant improvement of tribological behavior of AA 7075 was ascribed to the addition of the graphite particulates, which acted as a solid lubricant [18]. Baydoğan et al. studied the influence of retrogression and reaging (RRA) treatment on tribological properties of AA 7075 T6 under dry sliding conditions and found that when compared to the T6 temper, retrogression can obviously improve the wear resistance of AA 7075 while the corrosive wear resistance decreased after RRA treatment [19]. Despite these studies, the wear behavior of AA 7075 in petroleum industry has not attracted enough attention. Scientific experimental data on wear behavior of AA 7075 petroleum casing is still underreported.

Casing wear is mainly caused by the contact between rotating drill string and inner wall of casing [20]. The tribological behavior of casing is dependent not only on its material properties but also on the wear conditions, such as lubricated conditions and drilling parameters. For lubricated conditions, oil-based drilling fluid was proved to exhibit better lubrication performance than water based drilling fluid [21]. Current studies mainly focused on the influence of additives on lubrication performance of drilling fluid [[22], [23], [24], [25]]. As for the influence of drilling parameters on the tribological behavior of casing, rotation speed of drill string is the only controllable factor that influences casing wear [26]. As far as the authors are concerned, the effect of rotation speed on casing wear has rarely been studied, especially for AA7075 petroleum casing. It is of great importance to study the effect of sliding speed on tribological behavior of AA7075 petroleum casing not only from an engineering view but also a scientific view. On the one hand, it offers an opportunity to investigate the tribological performance of AA 7075. On the other hand, it offers a theoretical guidance for drilling engineers to safely use the AA 7075 petroleum casing, which is essential for reducing casing collapse and drilling accident induced by severe casing wear.

The objective of this study is to investigate the effects of sliding speed on tribological behavior of AA 7075 petroleum casing by pin-on-disc wear test. The wear and friction behaviors were represented by wear rate and friction coefficient. An in-depth study on the tribological behavior has been presented based on the morphology and element analysis of worn surfaces. We hope the results of this study can provides important reference for drilling engineers to reduce wear of AA 7075 casing.

Section snippets

Experimental materials

To simulate drilling environment, it is necessary to ensure the consistency of contact conditions of experiment and reality. For 88.9 mm drill string and 244.5 mm petroleum casing, their contact can be approximatively regarded as surface contact [26,27], thus, pin-on-disc contact geometry were employed to conduct all wear tests. AA 7075 alloy in T6 condition was used to manufacture discs and, 40CrNiMo steel (drill string material) was used to manufacture pins. Conventional oil-based drilling

Wear rate of the disc

Fig. 3 shows the wear depth distribution and wear rate of discs under different sliding speeds. The relationship of wear depth under different sliding speeds is summarized as follows: D0.628(65 μm)>D0.471(42 μm)>D0.0628(35 μm)>D0.157(32 μm)> D0.314(18 μm). The maximum wear depth at the highest sliding speed (0.628 m/s) is almost 2 times larger than that of low speed (0.0628 m/s and 0.157 m/s). At a middle sliding speed (0.314 m/s), the maximum wear depth is shown to be the smallest, which is

Discussion

Fig. 11 shows the change of drilling fluid temperature with time under different sliding speed. Due to the limitations of experimental conditions, it's not possible to measure the true temperature of the contact surface. The change of contact surface temperature can be described qualitatively through the analysis of variation of drilling fluid temperature. It is clearly seen that the drilling fluid temperature rises as time went by. At a higher sliding speed, the drilling fluid temperature

Conclusion

The effects of sliding speeds on tribological behavior of AA 7075 petroleum casing was studied in the present study. The main conclusion based on the results can be drawn as follows:

  • (1)

    The wear rate of AA 7075 petroleum casing decreases first and then increases as sliding speed increases from 0.0628 m/s to 0.628 m/s. While the mean friction coefficient decreases with the increasing sliding speed and its reduction rate decreased. The variation of wear and friction behavior were closely correlated

CRediT authorship contribution statement

Liangjie Mao: Conceptualization, Methodology, Investigation, Writing - original draft. Mingjie Cai: Writing - original draft, Data curation, Investigation. Qingyou Liu: Writing - review & editing. Yufa He: Writing - review & editing.

Declaration of competing interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgement

Authors thanks to the financial support of the National Key Research and Development Program of China (2018YFC0310202-01), Sichuan Science and Technology Project (2019YFS0045) and National Key Basic Research Program (973) “Well completion and test optimization in deep water oil and gas wells”(2015CB251205).

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