Edoardo Rossi Publications Content

Publications

PROCEEDINGS REFEREED

 1 Rossi, E., M. Kant, F. Amann, M.O. Saar, and P. Rudolf von Rohr The effects of flame-heating on rock strength: Towards a new drilling technology, Proceedings ARMA 2017, (in press). AbstractThe applicability of a combined thermo-mechanical drilling technique is investigated. The working principle of this method is based on the implementation of a heat source as a mean to either provoke thermal spallation on the surface or to weaken the rock material, when spallation is not possible. Thermal spallation drilling has already been proven to work in hard crystalline rocks, however, several difficulties hamper its application for deep resource exploitation. In order to prove the effectiveness of a combined thermo-mechanical drilling method, the forces required to export the treated sandstone material with a polycrystalline diamond compact (PDC) cutter are analyzed. The main differences between oven and flame treatments are studied by comparing the resulting strength after heat-treating the samples up to temperatures of $$650\, ^{\circ}C$$ and for heating rates ranging from $$0.17 \,^{\circ}C/s$$ to $$20 ^{\circ}C/s$$. For moderate temperatures ($$300-450 \,^{\circ}C$$) the unconfined compressive strength after flame treatments monotonously decreased, opposed to the hardening behavior observed after oven treatments. Thermally induced intra-granular cracking and oxidation patterns served as an estimation of the treated depth due to the flame heat treatment. Therefore, conclusions on preferred operating conditions of the drilling system are drawn based on the experimental results.

THESES

 1 Rossi, E. A Feasibility Study of a Combined Mechanical-Thermal Drilling System, MSc Thesis ETH Zurich, 81 pp., 2016. AbstractIn order to foster deep geothermal energy exploitation, a substantial reduction of the drilling costs is required. Spallation drilling is an alternative non-contact technique which would eliminate bit’s wearing related issues and increase the rate of perforation in hard crystalline rocks. However, its applicability is quite challenging and, furthermore, the spallation mechanisms do not work in soft rock formations. Therefore, a hybrid technique combining conventional mechanical and spallation drilling could be the sought breakthrough in the drilling research. Here, a flame-jet heats up the surface weakening the rock material which is then exported by PDC drill bits. An important advantage of this technique is the smoothening effect on the mechanical properties of the rock formation. Although literature presents a large amount of experimental studies about rock strength variation due to oven treatments, no investigations were found for the effects of flame thermal treatments. Therefore, an ad-hoc study is needed in order to precisely assess the consequences on the final strength of the material. Thus, in this work, the influences of temperature (until 650 ◦C), heating rate (from 0.17 to 40 ◦C/s) and confinement (until 150 Nm of tightening torque) on the material’s strength for Rohrschach sandstone and Grimsel granite are investigated. Material’s strength is measured by means of the scratch test and petrographic thin sections are used to vali- date the results. Data showed that the flame treatments lead to a monotonous decrease of strength with temperature, differently to the oven treatment where an initial increase of strength is observed. Regarding the final drilling application, two optimal operating conditions in terms of heating rate and maximum temperature are found. Besides, important variations of thermal diffusivity, conductivity and heat capacity with temperature are measured. The observed irreversible decay after the first heating cycle was justified by remarkable thermal cracking phenomena. Furthermore, an analytic approach based on Green’s functions has been developed in order to model the heat transfer phenomena for moving heat sources.

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PROCEEDINGS REFEREED

 1 Rossi, E., M. Kant, F. Amann, M.O. Saar, and P. Rudolf von Rohr The effects of flame-heating on rock strength: Towards a new drilling technology, Proceedings ARMA 2017, (in press). AbstractThe applicability of a combined thermo-mechanical drilling technique is investigated. The working principle of this method is based on the implementation of a heat source as a mean to either provoke thermal spallation on the surface or to weaken the rock material, when spallation is not possible. Thermal spallation drilling has already been proven to work in hard crystalline rocks, however, several difficulties hamper its application for deep resource exploitation. In order to prove the effectiveness of a combined thermo-mechanical drilling method, the forces required to export the treated sandstone material with a polycrystalline diamond compact (PDC) cutter are analyzed. The main differences between oven and flame treatments are studied by comparing the resulting strength after heat-treating the samples up to temperatures of $$650\, ^{\circ}C$$ and for heating rates ranging from $$0.17 \,^{\circ}C/s$$ to $$20 ^{\circ}C/s$$. For moderate temperatures ($$300-450 \,^{\circ}C$$) the unconfined compressive strength after flame treatments monotonously decreased, opposed to the hardening behavior observed after oven treatments. Thermally induced intra-granular cracking and oxidation patterns served as an estimation of the treated depth due to the flame heat treatment. Therefore, conclusions on preferred operating conditions of the drilling system are drawn based on the experimental results.

THESES

 1 Rossi, E. A Feasibility Study of a Combined Mechanical-Thermal Drilling System, MSc Thesis ETH Zurich, 81 pp., 2016. AbstractIn order to foster deep geothermal energy exploitation, a substantial reduction of the drilling costs is required. Spallation drilling is an alternative non-contact technique which would eliminate bit’s wearing related issues and increase the rate of perforation in hard crystalline rocks. However, its applicability is quite challenging and, furthermore, the spallation mechanisms do not work in soft rock formations. Therefore, a hybrid technique combining conventional mechanical and spallation drilling could be the sought breakthrough in the drilling research. Here, a flame-jet heats up the surface weakening the rock material which is then exported by PDC drill bits. An important advantage of this technique is the smoothening effect on the mechanical properties of the rock formation. Although literature presents a large amount of experimental studies about rock strength variation due to oven treatments, no investigations were found for the effects of flame thermal treatments. Therefore, an ad-hoc study is needed in order to precisely assess the consequences on the final strength of the material. Thus, in this work, the influences of temperature (until 650 ◦C), heating rate (from 0.17 to 40 ◦C/s) and confinement (until 150 Nm of tightening torque) on the material’s strength for Rohrschach sandstone and Grimsel granite are investigated. Material’s strength is measured by means of the scratch test and petrographic thin sections are used to vali- date the results. Data showed that the flame treatments lead to a monotonous decrease of strength with temperature, differently to the oven treatment where an initial increase of strength is observed. Regarding the final drilling application, two optimal operating conditions in terms of heating rate and maximum temperature are found. Besides, important variations of thermal diffusivity, conductivity and heat capacity with temperature are measured. The observed irreversible decay after the first heating cycle was justified by remarkable thermal cracking phenomena. Furthermore, an analytic approach based on Green’s functions has been developed in order to model the heat transfer phenomena for moving heat sources.