Emissions Big Picture: Metering Closes the Accuracy Gap

In business, it’s long been said that what gets measured can be managed. Naturally, the oil industry is keen to measure, and manage, greenhouse gas emissions. If it can also profit from what would otherwise be a waste stream? All the better. But how should these gases be measured—whether they are released during completion flowback operations, through flaring of associated gas at an oil field, or via leaks? Meters are an obvious go-to method for directly measuring emissions at the point of release, but satellites are increasingly being used for the big-picture—or, ahem, 30,000-ft—view they can provide. The use of satellites to monitor emissions raises an important question: how accurate is that big-picture view? That is a question Petroleum Development Oman (PDO) wanted answered as it worked to reduce its flaring volumes, and an SLB customer needed to understand it with regard to estimated emissions from completion flowback operations. In 2020, the World Bank’s Global Flaring and Methane Reduction (GFMR) Partnership issued a global gas flaring tracker report that ranked Oman, which had committed to the World Bank’s Zero Routine Flaring Initiative in 2016, as the 10th highest flaring country in the world. In the 2023 report, Oman had reined in its flaring levels enough to improve its standing to 13th. PDO was reporting flaring data to the World Bank, but the data used in the reports differed from what PDO supplied, Najma Al Waily, energy and water policy advisor at PDO, said during a technical session at SPE’s Annual Technical Conference and Exhibition (ATCE) in Houston in October. That discrepancy triggered a study to validate flare volume measurements using metered flare volume data and comparing that data to flared gas volumes estimated by Visible Infrared Imaging Radiometer Suite (VIIRS) Nightfire, which is generated from satellite-based observations. The study, described in SPE 228079, analyzed data from four PDO facilities selected due to “noticeable” data discrepancies, which were attributed to limited data availability, data synchronization issues, metering quality concerns, and inadequate satellite readings due to low flow rates. “We looked into the variance between the satellite data and our measurements in 2022 and 2023,” she said. PDO monitors flow rates using Class 4 ultrasonic flowmeters and uses practices like comprehensive flare meter mapping, a flare measurement dashboard, monthly flare gap-to-potential huddles, monthly flare meter health huddles for operational reviews, valve replacement/repair, and flare reporting audits to help it reduce its flare volumes, the authors wrote. The PDO team analyzed flowmeter readings obtained at 1-minute intervals from the flare sites and assessed the accuracy of VIIRS Nightfire data using two satellite calibration methods of those same sites in a bid to understand whether the World Bank’s flaring data for PDO assets may have been overestimated, she said.