A geospatial method to assess site suitability for static vehicle-based
measurements of methane plumes
Abstract
Vehicle-based methane-sensing systems are gaining popularity as tools
for monitoring site-level methane emissions from oil and gas (O&G)
sites. To measure emissions, vehicles equipped with methane sensors
intersect plumes along roads downwind of target sites and acquire
measurements in static (parked) or mobile modes. The downwind distance
between the emissions source and the measurement location is one of
several factors that must be considered in planning these types of
surveys. Here we present a method to estimate the suitability of O&G
facilities for vehicle-based measurements using downwind distances
recommended in OTM 33A and the tracer technique. We present two types of
analyses: (1) a historical analysis using weather reanalysis data and
(2) an operational analysis using forecast data. The method uses modeled
wind direction and geospatial data to identify O&G facilities that have
roads between 20 and 200 m downwind for OTM 33A and between 500 m and
3000 m downwind for the tracer technique. We apply the method to O&G
facilities in Alberta that will soon require annual or triannual LDAR
surveys. For the historical analysis we use ERA-Interim wind data and
calculate the vectorial average (resultant) of modeled winds for the
period 2009-2018. Of the 35047 O&G facilities examined, we find that
7% are, on average, suitable for OTM 33A and 69% are, on average,
suitable for the tracer technique, based solely on downwind distance. We
surmise that other factors like landcover, weather conditions (e.g.,
stability), and topography would likely reduce the candidate pool from
these estimates. We demonstrate the operational utility of the method by
examining a subset of 100 O&G facilities in southern Alberta and using
forecast wind direction from the Canadian High Resolution Deterministic
Prediction System (HRDPS), which has a 2.5 km grid spacing. We propose
that the method can be used as a screening tool to estimate site
suitability for static vehicle-based surveys and that it will likely
translate to mobile surveys once the effect of downwind distance is
clarified. Other factors can be incorporated in the method once test
results are available.