Evaluation of a PID wireless sensor network for monitoring VOCs near oil and gas wells

In this research, field and lab-scale tests were performed to evaluate the potential for wireless sensor networks (WSNs) to monitor composite total non-methane hydrocarbon (TNMH) concentrations near oil and gas production sites. A WSN was set up using photo-ionization detectors (PIDs) and telemetry equipment. The PIDs measure the TNMH levels by ionizing the compounds with a UV light and quantifying the ions produced with an electric field and an amplifying circuit. Field tests were performed at three different sites. The highest composite TNMH concentrations, greater than 110 ppmv (isobutylene equivalent), were measured at approximately 30 feet downwind from an unlit flare. The highest TNMH concentration measured off of an active well pad was 813 ppbv (isobutylene equivalent) at the fence line downwind of a frac pond. At a private ranch surrounded by active well pads, TNMH readings greater than the PID detection limit of ~1 ppbv were rarely detected. The field tests also demonstrated the feasibility of using a photovoltaic solar panel to provide power to PID sensors, as well as for acquiring continuous remote real-time PID readings. To compare the PID sensor TNMH readings with speciated VOC measurements, the air above a liquid condensate sample was analyzed in the lab using both a PID sensor and gas chromatography-mass spectrometry (GC-MS) analyses. As one example, a very strong correlation (r2 = 0.915) existed between the time-averaged PID TNMH readings and the time-averaged toluene concentrations. PID reading correlations with hexane and benzene were lower, probably due to the high vapor pressure of these compounds, which resulted in their being preferentially stripped from the condensate sample. Overall, this research demonstrated that wireless PID networks have significant potential for providing low-cost continuous real-time detection of VOC emissions at oil and gas production sites