Downhole gas pipe monitoring systems have an essential role in the extraction and monitoring processes of oil and gas. Since the most critical part of these systems is real-time data transmission, a novel transmission system is required to meet increasing bandwidth and capacity prerequisites. Therefore, visible light communication (VLC) becomes a significant emerging technology for downhole gas pipe monitoring systems in terms of high bandwidth and data rate. Following this direction, the VLC-based downhole gas pipe monitoring system is investigated by considering different modulation schemes and mediums. Specifically, a carbon steel-coated gas pipe channel is established with a transmitting light source and a photodetector to simulate the real field conditions of the VLC-based gas pipe monitoring system. Also, the well-known ACO-OFDM and OKK modulation schemes are employed and compared under real-world conditions. On the other hand, this study investigates for the first time the use of hydrogen gas medium, which is commonly employed to make lighter products from heavy petroleum fractions. Then, based on practical considerations, the performance of the VLC-based system is analyzed under different gases including nitrogen and hydrogen. Hence, for the performance metric, the bit-error rate is utilized and presented by considering the impact of internal pipe pressure and the circulating pump. As for the channel characterization of the hydrogen and nitrogen mediums, the channel impulse response is obtained and used to calculate the channel DC gain and path loss. Results demonstrate that the proposed VLC-based system achieves significant performance and is slightly affected by channel modifications.