Evaluating Natural Gas Emissions from Pneumatic Controllers from Upstream Oil and Gas Facilities in West Virginia

In April of 2018, an optical gas imaging (OGI) and full flow sampler (FFS) emissions measurement study of pneumatic controllers (PCs) at 15 oil and natural gas production sites in West Virginia was conducted. A total of 391 PC systems supporting 66 working wells were found. All were classified as snap-acting intermittent venting PCs (IPCs) that should ideally exhibit regular actuation cycles with cessation of supply gas emissions (low closed bleed rate) between actuation events. Using a PC-specific OGI inspection protocol with an assumed detection threshold band maximum of 2.0 standard ft 3 h -1 (scfh), 251 low actuation frequency IPCs passed OGI inspection indicating closed bleed rates likely below this level. A total of 140 liquid level IPCs were found with 132 of these servicing gas/liquid separation processing units (GPUs). These more frequently actuating and larger volume IPC systems exhibited OGI detectible continuous emissions in most cases. Time-resolved FFS measurements of methane (CH 4 ) emissions from liquid level IPC exhaust vents defined three basic categories, two of which were nonoptimal and were associated with higher emissions indicative IPC maintenance or process issues. Forty one percent of the liquid level IPC pilot exhaust vents exhibited normalized CH 4 mean emissions rates more than the 13.5 scfh whole gas IPC emission factor (EF) and possessed nonoptimal temporal emission profiles. The highest single IPC pilot vent emission was from a malfunctioning unit with a continuous CH 4 mean emission rate of 129 scfh. An analysis of FFS emission measurements compared to liquids production per IPC unit employed indicated that production sites operating at higher-than-normal liquid throughput rates had a higher potential for anomalous IPC operations and higher emissions. Due to combined liquid level IPC exhaust vents and other factors, OGI detection of potential maintenance issues was more difficult in these cases compared to low actuation frequency IPCs. Site engineering best practices that facilitate OGI diagnostics of liquid level IPCs during routine leak detection and repair (LDAR) surveys are described