Analysis of the wear of oil wells drill bits

Predicting the wear of drill bits is essential for all oil companies to maximise drilling efficiency and reduce loss in money and time. Typically, this problem has been dealt with by evaluating the specific energy of the drill bits at drilling formation intervals. Although this technique sometimes provides a good indication of the bit tooth wear, a number of phenomena such as bit balling and high vibration of the drill bit might give misleading results that affect the reliability of these techniques. Therefore, it is necessary to develop an effective predictive tool for the bit tooth wear rate by both experimental and theoretical approaches.
A case study is presented for the evaluation of the specific energy combined with dimensionless drilling parameters method as indicating tools for monitoring the wear of the roller-cone bits. The results were compared with the qualitative tooth wear index of the bits and an agreement was found for limited cases. The case study did not include the mechanical properties of the materials that form the bit, therefore a wear model was needed to combine the drilling parameters with the mechanical properties of the materials forming the bit under the phenomena of three body abrasion where the drill bits are in reality facing this effect. The new formula for quantifying the bit tooth wear is presented and compared with the qualitative bit tooth wear index, where close matching was obtained.
Experimental studies were carried out on polycrystalline diamond compact cutters from two manufacturers. The mechanical properties were determined by micro-indentation as well as nano-indentation testing on the diamond and the substrate layers of the cutters. Microstructural properties of the materials forming the PDC cutters found to be effective on the mechanical properties and consequently on the amount of wear. The volume of wear for the PDC cutters was determined experimentally using micro and nano-scratch tests of PDC cutters. The experimental wear was compared with the predicted wear based on current approaches in the literature. The results show that the wear of both layers of PDC cutters in this work can be predicted by the material mechanical properties and the applied load on the indenter. The analytical study based on various scanning electron microscopy techniques revealed that the main dominant wear mechanism for the substrate and the diamond layers is abrasive wear in the format of ploughing and cutting.