| Title | Overcoming Drilling Challenges with Rotary Steerable Technology in Deep Geothermal Wells in the Molasse Basin of Southern Germany |
|---|---|
| Authors | Lentsch, David; Savvatis, Alexandros; Schubert, Achim; Schoebel, Wolfgang |
| Year | 2012 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Drilling optimization; drilling performance; rotary steerable systems; Southern German Molasse Basin; deep geothermal wells; wellbore instabilities; complex 3D-wellpaths |
| Abstract | Several geothermal wells have been drilled successfully in the Southern German Molasse Basin within the last years. Some of them have reached depths of 4500 m with a horizontal displacement of up to 3000 m. However, as the wellpaths have become deeper and more complex, drilling has emerged as extremely challenging and cost-intensive, which can be critical for geothermal projects due to the high cost pressure. Usually conventional steerable motor systems were used to drill directionally, but the drilling performance was not sufficient. Penetration rates while sliding were typically 50-60% less than those obtained when rotating. Lower than the optimum weight on bit (WOB) was often applied to maintain direction. Poor weight transition, motor stall outs, high bit wear and low penetration rates were getting progressively worse with depth. In addition, weak drilling performance could have been a major factor for severe tectonic breakout in time-sensitive shales causing over gauge hole, stuck pipe and inadequate cementation. In order to avoid these problems, rotary steerable systems (RSS) have been deployed in two recently drilled wells. The result was a step change in well delivery time and reduced drilling cost. Moreover, no borehole stability problems have been encountered since drilling with RSS. This paper presents a case study demonstrating that the change from conventional systems to RSS has been both, technically and commercially successful. |