Title:

Thermal Spallation Drilling an Alternative Drilling Technology for Deep Heat Mining - Performance Analysis, Cost Assessment and Design Aspects

Authors:

Michael A. KANT, Edoardo ROSSI, Dragana HÖSER, Philipp RUDOLF VON ROHR

Key Words:

spallation drilling, drilling velocity, costs, design, applicability

Conference:

Stanford Geothermal Workshop

Year:

2017

Session:

Drilling

Language:

English

Paper Number:

Kant2

File Size:

811 KB

View File:

Abstract:

In order to promote the development of geothermal energy production from deep resources, cost effective solutions to increase the drilling performance in hard rock formations have to be developed. Currently, the drilling costs account for up to 70% of the total investment for a deep geothermal project. Therefore, several emerging technologies are currently investigated by researchers around the world. One of these alternative technologies is the spallation technology, which is based on the effect of hard, crystalline rocks disintegrating into small fragments, if rapidly heated by a hot fluid jet. Spallation drilling features high penetration rates in hard rock formations, an efficient energy transport to the bit and significantly reduced wear-rates. Previous research has indicated that these benefits could lead to a significant decrease of the drilling-costs and therewith to a boost of the development of geothermal energy production from deep resources. The efficiency and the applicability of spallation drilling can be significantly increased with a profound knowledge of the process itself. Therefore, we present a novel model which is capable to estimate the possible drilling velocity and the involved costs of the spallation process. This model is based on an analytical approach and considers various influences as the applicable operating range where spallation can be used, the impact of various rock properties and the heat transfer characteristics of the hot fluid-jet. Besides the possibility to estimate drilling velocities, the experimentally validated model can also be used for the design of spallation drill bits with respect to an appropriate selection of flame temperatures, heat transfer coefficients and jet flow rates. This allows a performance analysis of the technology for drilling in various different rock formations.


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