Abstract
To improve the economics and viability of accessing deep georesources, we propose a combined thermo–mechanical drilling (CTMD) method, employing a heat source to facilitate the mechanical removal of rock, with the aim of increasing drilling performance and thereby reducing the overall costs, especially for deep wells in hard rocks. In this work, we employ a novel experiment setup to investigate the main parameters of interest during the interaction of a cutter with the rock material, and we test untreated and thermally treated sandstone and granite, to understand the underlying rock removal mechanism and the resulting drilling performance improvements achievable with the new approach. We find that the rock removal process can be divided into three main regimes: first, a wear-dominated regime, followed by a compression-based progression of the tool at large penetrations, and a final tool fall-back regime for increasing scratch distances. We calculate the compressive rock strengths from our tests to validate the above regime hypothesis, and they are in good agreement with literature data, explaining the strength reduction after treatment of the material by extensive induced thermal cracking of the rock. We evaluate the new method’s drilling performance and confirm that thermal cracks in the rock can considerably enhance subsequent mechanical rock removal rates and related drilling performance by one order of magnitude in granite, while mainly reducing the wear rates of the cutting tools in sandstone.
Highlights
The construction of wells, for example to extract oil, gas or heat from underground reservoirs requires substantial financial investments, which are mainly related to the involved drilling operations (Tester et al 2006; Akin and Karpuz 2008; Petty et al 2009; Lukawski et al 2014; Diaz et al 2017)
To improve the economics and viability of accessing deep georesources, we propose a combined thermo–mechanical drilling (CTMD) method, employing a heat source to facilitate the mechanical removal of rock, with the aim of increasing drilling performance and thereby reducing the overall costs, especially for deep wells in hard rocks
Tool penetration we present the experiment findings concerning the penetration of the cutting tool along the scratch distance
Summary
The construction of wells, for example to extract oil, gas or heat from underground reservoirs requires substantial financial investments, which are mainly related to the involved drilling operations (Tester et al 2006; Akin and Karpuz 2008; Petty et al 2009; Lukawski et al 2014; Diaz et al 2017). The current trend of accessing deeper underground resources poses challenges for the overall project economics, as the costs increase exponentially with well depth (Fitzgerald 2013; Abdo and Haneef 2013; Hu et al 2013) This is especially unfavourable for enhanced geothermal systems (EGSs) (Barbier 2002; Stefánsson 2002; Tester et al 2006; Yost et al 2015), which are. Of hard (basement) rocks, results in poor drilling performances, in terms of high drill bit wear rates and low rates of rock penetration This results in significant non-productive time, expensive tool replacements and poor process efficiencies, which drive up the overall project costs (Fay 1993; Wise et al 2002; Diaz et al 2017; Blankenship et al 2005; Raymond et al 2012). Recent drilling research has focused on implementing innovative solutions to improve the overall drilling process in hard rocks (Teodoriu 2011; Anders et al 2015; Kant et al 2017; Rudolf von Rohr et al 2017; Kant et al 2018; Reinsch et al 2018; Beentjes et al 2019)
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