Tank Vapors – If you think measuring above ground storage tank vents is boring, think again! Keeping emissions in check is no joke, folks

Quite often, we work with producers who are looking to eliminate emissions from above ground storage tanks, among other sources.  As it is difficult to accurately identify the volume of gases emitted, we have put together a review of tactics and strategies to overcome this obstacle and get a more accurate reading.

NOTE: There are approximately 12,000 production tanks in operation in Alberta. 88% are at oil batteries.

Oil Single-well batteries without separators were found to vent persistently at 50 m3/day to 500 m3/day (CERIN 2023).

A study published in the Elementa Journal describing the methane venting from uncontrolled storage tanks at conventional oil wells offer valuable insights and recommendations aimed at enhancing the precision of tank vent measurements and greenhouse gas (GHG) reporting.

The study highlights the importance of using GIS data cautiously for estimating gas venting volumes. It recommends only using data from wells with separators, where vented gas likely occurs due to liquid flashing in tanks. For wells that directly send gas and oil to storage tanks, measurements are necessary to accurately assess gas venting. Furthermore, continuous venting after well shutdown indicates that there may not be a consistent relationship between vent volumes and oil production, challenging the use of Gas-Oil-Ratio (GOR) estimates. While regulations in Alberta limit the use of GOR for estimating venting, there is no clear guidance on how to distinguish between different well scenarios. To address this, selective continuous or time-averaged measurements can provide valuable insights (Zavala-Araiza, 2018).

To accurately measure tank venting, a longer minimum measurement time is needed. In Alberta, the recommended minimum has increased from 1 hour to 24 hours. This is consistent with the time required for GOR measurements in Alberta and Utah, and for storage tank emissions in Texas. This extension ensures that measurements are precise within 10% at least 95% of the time (Festa-Bianchet, 2023). Additionally, it is important to note, a 24hour measurement will not necessarily provide peak flows, which are important for sizing methane abatement equipment (i.e. Enclosed Combustor, VRU’s).

Alternatively, should direct measurement approaches be employed, careful consideration must be given to the specific methodologies and instrumentation utilized (CERIN, 2023). One such direct measurement, the Fox Thermal mass meter showed good results when measuring tanks vapors.

Efforts are being undertaken at Southern Alberta Institute of Technology (SAIT) to develop a user interface that producers and regulatory bodies can use to determine accurate estimation of methane from oil tanks (CERIN, 2023). Modelling of tanks has identified some key constraints and considerations for inputs. This technology if not finalized but will be a convenient solution when completed.

Aerial measurement is also used to collect methane emission information from many sites quickly.  When using this methodology it is important to understand that aerial survey, like one completed by Bridger Photonic, can only detect methane when it is present. Meaning, when the plane fly’s over the site it will only detect methane if it happens to be venting at that time (Johnson, 2021).

In essence, the findings underscore the importance of refining measurement techniques and duration protocols to enhance accuracy and reliability in assessing tank venting and GHG emissions.

 

-Joseph R. Roscioli, Scott C. Herndon, Tara I. Yacovitch, W. Berk Knighton, Daniel Zavala-Araiza, Matthew R. Johnson & David R. Tyner (2018) Characterization of methane emissions from five cold heavy oil production with sands (CHOPS) facilities, Journal of the Air & Waste Management Association, 68:7, 671-684

-Festa-Bianchet, SA, et al. 2023. Methane venting from uncontrolled production storage tanks at conventional oil wells—Temporal variability, root causes, and implications for measurement. Elem Sci Anth, 11: 1.

-Mathew Johnson, David Tyner, Alexander Szekeres, 2021. ‘Blinded evaluation of airborne methane sources detection using Bridger Photonics LiDAR’. Elsevier

CERIN Canadian Emissions Reduction Innovation Network. 2023 ‘Accurate Methane Emissions Measurement and quantification from petroleum storage tanks – computational model.

CERIN Canadian Emissions Reduction Innovation Network.2023 ‘Methods for Estimating Emissions from Tanks.