Microwave system development for wireless communications and liquid level determination inside metallic pipes for oil and gas wells

Abstract

A classic wireless propagation system between a transmitter and a receiver is well defined in the literature. One propagation scenario not very well researched is within enclosed environments such as pipes, tunnels, or mines. To explore such topics, the research in this thesis examined the theoretical modelling, design, implementation, and test of two different RF/microwave systems for applications within oil and gas wells. In particular, one system developed communications within a circular metallic pipeline, and the other was the liquid level determination of the crude by considering electromagnetic propagation within coaxial pipelines. The transceivers for those systems were placed into conventional circular and coaxial metallic pipes prevalent within real-world oil and gas well systems. Project work collaborated with The Oil and Gas Innovation Centre (OGIC) and Innerpath Technologies Ltd., both situated within Aberdeen, UK.

An original feasibility study was first developed where the well was modelled as a circular aluminium pipe and then considered an overmoded pipeline when treated like a microwave waveguide for the communication system. This is not conventional as typical microwave waveguide systems try to ensure unimodal operation over the required frequency range. Regardless, pipe testing was completed by considering commercially available oil and gas well pipelines, and as the transceivers, half-wave dipoles operating at 2.5 GHz were employed. Due to this excitation technique and the enclosed environment, parameters such as the propagating mode, the directivity, and the realized effective gain of the antennas also needed to be studied for this scenario. This brought new findings to the antennas and propagation research communities. Additionally, a numerical transmission path loss (TPL) model was developed and verified using full-wave simulations and lab measurements. Sensory data, including temperature and pressure within the pipe, were then transmitted using N210 universal software radio peripheral (USRP) modems by National Instruments and coded using orthogonal frequency-division multiplexing (OFDM). Since this initial study was experimentally verified and successful, a more advanced transceiver and mechanical antenna housing was designed and measured, which is even more realistic for industrial oil and gas well pipelines. In particular, compact PCB-based end- re antennas were designed for signal propagation within a circular pipeline considering corroded carbon steel. A specific link budget was also developed for this S-band transmission system and measured successfully using a 36 meter carbon steel pipeline, which could have been easily extended to more than 150 meters. Also, based on the measured system data, the receiver sensitivity was -77 dBm and 15 dB in terms of the signal-to-noise ratio (SNR). Additionally, some digitized images and live videos were successfully transmitted and monitored in real-time using the N210 USRP modems. The employed antenna and its protective RFi mechanical housing were also designed to be positioned within a mandrel for protection from possible gaseousflow and the filling material within the pipeline. Such a system could be adopted for industry-standard oil and gas wells. In terms of the RF/microwave liquid level determination system, the position of the crude was determined by measuring the time delay between the original signal and the reflected one from the liquid layer positioned at the bottom of the well. To conform to standard pipeline dimensions, the propagating mode was selected as a superposition of the TE21 and the TE31 modes, which again is not standard. Theory, full-wave simulations, and measurements verified the wave velocity for the generator signal and the propagation within the guide. Then, the transmission signals were selected as Gaussian and rectangular pulses. A dedicated link budget was also developed for the 2.4 GHz microwave system and measured successfully in the lab using a carbon steel pipeline. Based on these initial experiments, the maximum investigation depth for the proposed system can be 250 meters when the stimulating power is 1 kW. All these electromagnetic transmission studies realizing antenna-driven propagation were supported by theory, full-wave simulations, as well as system-level measurements, which approached high levels of technical readiness.