Measuring Emissions That Matter: Strategies for Dealing with Offsite Emissions

The problem with offsite emissions

In areas of high density oil & gas, mixed-use industrial, and agricultural development, it can be difficult to determine the source of a greenhouse gas emission. If an emission from an offsite source is attributed to an operators site it can lead to:

• Difficult land owner relations due to odor complaints

• Employee and contractor HSE concerns due to H2S, VOCs, or other hazardous emissions

• Operations and maintenance crews searching for emission sources that either do not exist or that originated from somewhere else

• Incorrect quantification of site-level emissions due to inclusion of offsite sources

There are two components to understanding the source of emissions using continuous monitoring.

The first step is to collect a suitably rich set of wind data - specifically, wind speed and direction. The data does not lie. In deployments of Qube's Axon devices to our customers' sites, we have observed meaningful variance in wind data collected by devices that are less than 100m (300 ft) from each other (Figure 1).

Figure 1 - Variation in wind speed and direction on the same site

Some continuous monitoring solutions deploy a single anemometer to sites, collecting a single source of wind speed and direction which results in a simplified representation of the wind vectors on a site.  In figure 2, two possible emission sources are illustrated with red and blue circles. If a single wind data point is measured, it can be difficult to determine if the source is the red circle or the blue circle. When multiple wind measurements are collected, a more representative vector field can be modeled which improves confidence that an emission originated at the red circle.

Figure 2 - Tracking possible emissions sources

In both panes, the red and blue circles are possible emission sources. The left pane shows a simplified wind vector array that results from a single wind measurement. The right pane shows how the vector field can change with more measured data.

It is easy to imagine a situation where field operators & contractors are asked to confirm a leak identified by a continuous emissions monitoring system using an Optical Gas Imaging (OGI) camera and struggle to find an emission source where a wind vector array localizes to incorrect equipment on site or incorrectly classifies an emission as originating onsite. Chasing false positive emissions costs companies time and money. By collecting additional wind data, field operators and contractors can more efficiently confirm and repair leaks.

The second component to understanding offsite emissions is incorporating measured gas concentrations, wind speed, and wind directions into software algorithms. The focus of this post is on the filtering of emissions - so we will leave detailed discussion about localizing and site-rate calculations for another day.

By comparing gas concentration to the wind direction, carefully designed software algorithms are able to determine if gas arrived at the sensor from an onsite or offsite source. For example, in Figure 3 we see how measuring wind direction at multiple locations allows for the determination of whether a particular emission likely originated onsite (red arrows) or if it originated at an offsite source (gray arrows).

Figure 3 - Measuring the angle of wind

Red arrows indicate onsite emission sources blown to blue and yellow sensors. Gray arrows indicate offsite emissions sources that were detected at the red and green sensors. By measuring the angle of the wind, Qube can confidently determine if a detected emission originated onsite or offsite.

A common land owner relations problem that oil and gas companies face is odor complaints from adjacent land owners and residents. These complaints are particularly prevalent in areas of high density oil development where multiple oil and gas operators have drilled wells and constructed production facilities. Land owners and residents can be quick to blame immediately adjacent production facilities for any unpleasant odors that the wind blows to their residence. Continuous monitoring devices can help companies improve land owner relations by providing valuable air quality data that can be directly used in land owner communications. If a leak is determined to have originated offsite, this can be communicated to a landowner.

Additionally, implementing continuous monitoring for gases such as VOCs and H2S can help companies be aware of potential HSE issues related to employees and contractors exposure to these harmful gases. Knowing and identifying an emissions source is the first step. VOC and H2S exposure should be minimized with properly operated equipment, however, operating can conditions change, equipment may fail outside of expected maintenance windows, and adjacent production facilities may not be operated to the same standard.

Qube’s Continuous Monitoring Solution

The Qube Solution combines on-site Axon devices with cloud analytics and dashboards to effectively detect, quantify, and manage offsite emissions sources.

Each Axon device is fitted with individual anemometers (wind speed and direction) allowing for the creation of a more sophisticated wind vector mesh and providing greater certainty to the origin of a particular emission. Field measured gas concentrations, wind speed & direction, temperature, humidity, and barometric pressure are fed from Axon devices into Qube’s dashboards, allowing customers to filter emissions as originating onsite or offsite, localize emissions to equipment groupings, and compute site-wide emission rates. Offsite emissions are omitted from total site-rate calculations.

By deploying continuous emissions measurement systems such as Qube's Axon devices to their production facilities, leading oil & gas operators are able to:

• Measure what matters by filtering out offsite emissions from site-specific emissions quantifications.

• Deploy maintenance crews with confidence that an alert generated by the Qube platform is a result of an onsite source. No more chasing false positive detections.

• Improve stakeholder relations by collecting definitive data regarding emissions from your facility.

Learn more about Qube’s Continuous Monitoring Solution