| Title | Case Studies of PDC Bits in Deep Geothermal Drilling |
|---|---|
| Authors | Terence COUDERT, Adrian AMBRUS, Dapeng ZHAO, Hans LANGE, Alexandre KANE, Massimo LUCHINI, Corrie GRANT, Kjell HAUGVALDSTAD, Geoffrey MCELNAY |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | PDC drill bit, geothermal well, model-based ROP prediction, bit damage |
| Abstract | The vast majority of drill bits currently used in geothermal applications are of the roller cone (RC) type, while the preferred drill bit type in oil & gas wells is the PDC (Polycrystalline Diamond Compact). Geothermal drilling applications are usually characterized by hard (and at times abrasive) formations that represent a significant challenge for conventionally shaped cylindrical PDC cutters due to their tendency to sustain wear in such formations. The preference for RC bits in geothermal applications is due to their ability to drill just about any rock type in a predictable manner and at a relatively low cost. However, RC bits use rotating cones that only last a certain number of hours (revolutions) before the bit has to be pulled out of the well to be replaced. In recent years advances in PDC technology have enabled the manufacturing of novel cutter and bit designs for hard rock drilling. Through the research project INNO-Drill two well sections have been drilled in 2018 and 2019, in metamorphic rock formations in the Larderello region in Italy, using two distinct PDC drill bits provided by the industrial partners. The first drill bit had conventional PDC cutters and was used in the 12¼†section of the well (at 1416-1476 m depth). This section used a bottom-hole assembly instrumented with high frequency downhole sensors. The second drill bit, with conically shaped PDC inserts, was used in the 8½†section (at 2400m and at 3500m depth) of the well with surface data acquisition only. The results are presented through drill bit damage analyses, and post-processing of recorded data (rotary speed, weight on bit, torque on bit, downhole vibrations, rate of penetration) to assess and better predict the drilling performance. A physics-based model of the bit-rock interaction was used to facilitate drilling performance prediction and characterization of drill bit damage. The analyses indicate a good correlation between the calculated damage parameters and the bit condition observed after pulling out, while the model-based ROP predictions match the trends observed in the recorded data. |