On the Investigation of Carbon Dioxide Medium for VLC based Downhole Telemetry System

Data transmission between the downhole and surface called the downhole telemetry system is a critical part of monitoring and extraction processes in the oil and gas industry. Numerous real-time data transmission techniques for downhole telemetry systems have been implemented, however, growing demands of higher bandwidth and data rate for downhole communications made it necessary to find a new, reliable, and low-cost communication system. In this area, visible light communications (VLC) with a huge available spectrum providing high bandwidth and data rate are indispensable opportunities for downhole telemetry systems. This paper addresses the issues related to the VLC usage in downhole gas pipeline telemetry/monitoring systems. To emulate real field conditions, a carbon steel coated and carbon dioxide-filled gas pipeline is created with a circulating pump and a pressure gauge, and the VLC setup is established. The performance of a VLC system employing an asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) modulation technique with 128-FFT and guard band is practically tested by taking channel estimation and synchronization into account. Moreover, the channel impulse response of the carbon dioxide-filled gas pipeline is presented along with a proposed path-loss model. The BER against SNR performance of the proposed downhole telemetry system is investigated for carbon dioxide gas at atmospheric pressure. Furthermore, the effect of the circulating pump and different colors of led on system performance is presented. Measurement results of the free-space air medium are also included as a benchmark.