Wear factors and mechanisms of L-80 steel casings

Casing wear in directional drilling is inevitable and may result in catastrophic failure of the casing column. It is thus essential to understand its mechanisms and quantify its extent by estimating the casing wear factor. In this research, actual field casing samples, drilling pipe joints and muds were considered. An in-house built testing facility was used to test several L-80 casing samples by considering three rotational speeds of the drill pipe tool joint (DP-TJ) (115, 154, and 207 rpm) and three side loads (1000 N, 1200 N and 1400 N). The influence of the water- and oil-based muds on the coefficient of friction, wear volume, wear factor and wear mechanisms were investigated. The results revealed that under water-based mud (WBM) lubrication casing wear volume and wear factors were more than twice that of oil-based mud (OBM) lubrication. Moreover, it was observed that as the side load increased under both OBM and WBM lubrication at a constant rpm, both wear volume and wear factor increased. However, increasing the rotational speed while maintaining the side load constant decreased the wear factor, owing to the localized softening effect caused by the high heat generation at the contact area and the possible hydrodynamic lubrication regime change at higher speeds. The analysis of the digital microscopic images taken at the wear region shows that abrasive mechanism was dominant in the case of OBM lubrication. On the other hand, both abrasive and adhesive wear mechanisms were present under WBM lubrication.