SPALL-APP – Untersuchung der Anwendbarkeit eines kombinierten thermomechanischen Bohrsystems für tiefe geothermische Ressourcen

• Research unit: SFOE
• Project number: SI/501658

Key words (English)

Thermo-Mechanical Drilling Method, Rock-Bit-Flame Interaction, Geothermal Energy, Implementation Possibilities, Enhanced Drilling Performance, Triaxial Testing

Short description (German)

Ein kombiniertes thermomechanisches Bohrverfahren ist ein neuartiger Ansatz zur Steigerung der Leistung von Bohrungen für die Tiefengeothermie. Ein heisser Fluidstrahl wird verwendet, um das Material zu schwächen und erleichtert daher das nachfolgende Entfernen des Gestein durch konventionelle Bohrmeissel. Im vorgeschlagenen Forschungsprojekt sollen folgende Ziele verfolgt werden: Untersuchung der optimalen Betriebsbedingungen eines thermo-mechanischen Bohrverfahrens, Implementierung der Technik im Feld und Optimierung des Prozesses.

Short description (English)

A combined thermo-mechanical drilling method is a novel approach to increase the performance of deep geothermal drilling. A hot jet is used to weaken the material and therefore facilitating the subsequent abrasive removal performed by conventional drilling cutters. The following goals are pursued: optimal conditions of the thermo-mechanical drilling approach, an implementation of the technique in the field and a further optimization of the process.

Final report (English)

Deep geothermal resources can play a key role in future energy supply systems. However, drilling of deep wells, to access these deep geo-resources in hard crystalline rocks, poses major challenges for conventional drilling technologies (e.g., rotary drilling). The poor performances of conventional drilling methods in hard rocks, in terms of wearing of the drill bits and low penetration rates, yield significant non-productive time, frequent drill bit replacements and low process efficiency, which in turn hinder the economic viability of accessing deep energy resources. Hence, with the aim of improving the economics of the drilling process to access deep energy resources, in this work we investigated novel drilling technologies, namely thermal spallation drilling and Combined Thermo-Mechanical Drilling (CTMD). The latter technology is based on the concept of providing thermal assistance to conventional mechanical drilling. In this way, the flame jet can induce: (a) the thermal spallation onset, when the rock exhibits the required properties for thermal spallation of the rock; or (b) the thermal weakening of the rock material (flame-assisted rotary drilling), which is characterized by a more efficient removal process, performed by the drilling cutters. In this work, we investigated the viability of the concept, first through laboratory experiments, then by implementing the technology prototype into a real-scale drill rig and testing the technology in the field. Lastly, numerical simulations were performed to investigate further the thermal spallation mechanism of the rock.

Related documents

• Final Report [PDF] 252 kB