Dans de nombreuses régions du monde, d’immenses réserves gazéifères dites non conventionnelles sont piégées dans des roches faiblement perméables qui ne peuvent pas être exploitées par des méthodes de forage classiques. Bien que très controversée, la seule méthode d’exploitation de ces gisements repose actuellement sur la technique de fracturation hydraulique. Pour ces raisons, une collaboration de recherche a débuté en 2007 entre la société TOTAL et le Laboratoire de Génie Electrique de l’université de Pau (récemment devenu le laboratoire SIAME), visant à étudier l’opportunité d’utiliser la fracturation électrique comme solution alternative à la fracturation hydraulique. Cette méthode repose sur un procédé dynamique de fracturation de la roche par application d’une onde de pression créée suite à l’initiation d’un arc électrique dans un liquide. Ce travail, financé par TOTAL dans le cadre d’une bourse CIFRE, s’inscrit dans la continuité de travaux déjà engagés sur cette thématique et vise particulièrement à approfondir les connaissances concernant le cœur du procédé de fracturation : la décharge électrique dans l’eau et la caractérisation de l’onde de pression résultante. Dans cette optique, l’importance du circuit et des paramètres électriques de l’arc a été démontrée en termes d’injection de courant et de transfert de puissance. Une formule empirique permettant de prévoir la valeur de la pression dynamique a, par conséquent, été établie. Afin d’optimiser le rendement électro-acoustique, une étude spécifique a été menée sur l’effet du mode de rupture diélectrique du fluide. Ces travaux ont également permis de proposer des solutions concernant le contrôle de la dynamique de l’onde de pression. Enfin, les effets des propriétés thermodynamiques du fluide sur sa rigidité diélectrique, sur la consommation d’énergie, ainsi que sur la propagation de l’onde de pression ont été analysés afin d’établir une série de conclusions permettant d’optimiser le procédé. / Numerous parts of the world contain huge unconventional gas reserves which are located in low permeability rocks, and consequently, cannot be produced by classical drilling techniques. Besides its numerous detractors, the only currently available method to exploit these reservoirs relies on hydraulic fracturing. For these reasons, a research collaboration was started in 2007 between the Total Company and the Electrical Engineering Laboratory of Pau university (recently renamed SIAME Laboratory). The main goal was to study the potential concerning the use of the electrical fracturing technique as an alternative to hydraulic fracturing. This method is based on a dynamic rock fracturing process through the applying of a pressure wave enhanced by the generation of an electrical arc into a liquid. This work, which is financed by TOTAL through a CIFRE funding, follows the track initiated on this topic and mainly intends to improve the knowledge concerning the critical part of the fracturing process: the electrical discharge in water and the resulting pressure wave characterization. In this purpose, the importance of the circuit and of the arc electrical parameters was demonstrated in terms of current injection and power transfer. An empirical formula used to predict the dynamic pressure value has consequently been established. In order to optimize the electro acoustic efficiency, a specific study was performed on the liquid dielectric breakdown modus. This work allowed us to suggest new solutions concerning the dynamic pressure wave control. Finally, the fluid thermodynamic properties effects on its dielectric strength, on the energy consumption, and on the pressure wave propagation were analyzed in order to draw conclusions for the process optimization.

This diploma thesis is focused on the plasma surface treatment of historical glass from the 18th and 19th centuries by low temperature electrical discharges in solutions of sodium chloride and potassium carbonate and finding the most suitable settings of conditions for the surface cleaning. Stainless steel electrode and a specially designed electrode system with wolfram wire in the quartz glass capillary were used for the generation of discharge using an audio frequency power supply. Each line of samples was made from one piece of historical glass that was cut to smaller pieces. All cleaned samples were photographed before and after the cleaning so the possible changes of the cleaned area could be visually compared. Then the samples were analysed by LA-ICP-MS (line scanning of surface), where was analysed the cleaned area of samples, and values were compared to the analysis of the reference sample that was not cleaned. Examined isotopes of elements were selected on the basis of the supposed composition of glass, corrosion products, and soil at the place of discovery. Analyses were standardized by NIST 610. Acquired values were transferred to oxides. The most important oxides (Na2O, MgO, SiO2, P2O5 a K2O) were chosen for deciding the most effective cleaning settings. It was decided that the most effective setting for cleaning was the one where the biggest difference of values between sample and reference occurred. Four series of these solutions were compiled and one parameter was changed for each of them. Solutions and their conductivity, frequency of the power supply, and time of cleaning were chosen as changing values. Three samples of different times of cleaning were cleaned without interruption. The time of cleaning was split into intervals of 30 seconds of cleaning and 1 minute of non-action for another two samples of this series. In this way we were trying to find out if the following surface analysis will be influenced by the diffusion of the particles into the sample, or not. The frequency of power supply was recorded and its dissipated power was calculated for each measurement. Emission spectra of a series of different solution conductivity were measured before cleaning of samples. Measurement of OES was made with the ignition of discharge so the active species of plasma were shown in spectra. These species are probably participating in the cleaning process of glass. Emission spectra were also measured after cleaning to find out if values of active species were changed or unknown spectral lines appeared. These lines should be from dirt and corrosion products that were cleaned from the surface of the glass. It was found out that the most effective cleaning of sample 1 (series where the conductivity of the NaCl solution was changed) was done in a solution of conductivity 900 S/cm. The most effective cleaning of sample 4 and sample 7 (series where the conductivity of the K2CO3 solution was changed) was done in a solution of conductivity 600 S/cm. The most effective cleaning of sample 6 (series where the frequency was changed) was done at frequency = (15200 ± 30) Hz. The most effective cleaning of sample 5 (series of different cleaning times) lasted seven minutes without time delay. The future research it should be appropriate to try a combination of these most effective cleaning settings on the surface of more samples, so the finding of this thesis will be confirmed.