Influence of oil-water ratio on the wear of Cr13 casing lubricated with drilling fluid

Abstract This work studies the influence of oil-water ratio on the wear behavior of casing lubricated with drilling fluid using a pin-on-disc tribometer. The disc samples and pin samples are made of Cr13 steel and G105 steel, respectively. Three-dimensional profiles, SEM images and cross-sectional images were used to observe the wear morphology. The XRD and polarization curves analyses were employed to analyze the wear mechanisms under different oil-water ratios. Results showed that the addition of diesel oil into drilling fluid can significantly reduce casing wear. The wear rate and mean friction coefficient decrease first as oil-water ratio increases from 0 to 3 and then increase when oil-water ratio continues to increases from 3 to 5. Exorbitant oil content prevents the loss of friction heat, resulting rapid rise in drilling fluid temperature and significant improvement of Cl− activity. Therefore, the corrosion rate is increased and the corrosive wear dominates the wear process as oil-water ratio increases from 3 to 5. The main wear mechanism of casing lubricated with drilling fluid is abrasive-corrosive wear, and the dominant wear type is abrasive wear when the oil-water ratio is 0–2 while corrosive wear when the oil-water ratio is 3–5. During drilling, on the premise of meeting drilling requirements, controlling the oil-water ratio of drilling fluid to about 3 can effectively reduce the wear of Cr13 steel casing.