Wireless communication system in confined media : material characterization and antenna design

The growing use of wireless transmissions these past few years has lead the industry to consider these techniques with an increased interest. The advantages of using Wi-Fi transceivers to inter-connect industrial devices are numerous, in terms of infrastructure costs, versatility, and sometimes, reliability and data rate. Along with these efforts, Schlumberger has launched several actions to validate the use of wireless techniques in the oilfield business. The oilfield tools are collecting data during the drilling phase, that is stored in memories. When the tool is back at the surface, this data has to be transmitted to a computer. This operation is currently done through a slow cable connection. Performing this dump with a wireless communication system can help save time. The environmental conditions downhole are very stringent : high pressure, high temperature, important shocks and aggressive chemicals. As a consequence, oilfield tools adopt a circular geometry, and are made from specific materials, most of them being metallic, with seldom dielectrics. High-frequency permittivity measurements of the dielectric materials used in the oilfield business have been carried out. Materials suitable for high-frequency application have been selected. In this context, an antenna operating in the Wi-Fi band (2.4 - 2.5 GHz) has been designed. This antenna has to be buried in a small metallic hole, machined in the oilfield tool. The circular hole, considered as a waveguide section short-circuited at one end, exhibits a cutoff frequency that is above the band of interest. There are two important consequences : the "cavity" adds a capacitive load that helps to reduce the operating frequency, and attenuates the part of the energy radiated by the backside of the antenna. The whole system is contained in a circular metallic hole with a diameter equal to 29.8 mm and a depth of 10.8 mm. The efficiency is above 50% for the whole band, with a gain between 4 and 5 dB, and a 3dB angle around 110°. Finally, an oilfield platform is completely built with metallic beams for the rig, and metallic panels for the cabins. Thus, there is a lot of scattering and reflection. The signal coverage of Wi-Fi equipment has successfully been tested on a real rig. These results show that wireless communication system for oilfield applications are very serious candidate for next generation dump tools.Doctorat en sciences appliquées (FSA 3)--UCL, 200