Assessment of Methane Emissions from Oil and Gas Production Pads using Mobile Measurements

A new mobile methane
emissions inspection approach, Other Test
Method (OTM) 33A, was used to quantify short-term emission rates from
210 oil and gas production pads during eight two-week field studies
in Texas, Colorado, and Wyoming from 2010 to 2013. Emission rates
were log-normally distributed with geometric means and 95% confidence
intervals (CIs) of 0.33 (0.23, 0.48), 0.14 (0.11, 0.19), and 0.59
(0.47, 0.74) g/s in the Barnett, Denver-Julesburg, and Pinedale basins,
respectively. This study focused on sites with emission rates above
0.01 g/s and included short-term (i.e., condensate tank flashing)
and maintenance-related emissions. The results fell within the upper
ranges of the distributions observed in recent onsite direct measurement
studies. Considering data across all basins, a multivariate linear
regression was used to assess the relationship of methane emissions
to well age, gas production, and hydrocarbon liquids (oil or condensate)
production. Methane emissions were positively correlated with gas
production, but only approximately 10% of the variation in emission
rates was explained by variation in production levels. The weak correlation
between emission and production rates may indicate that maintenance-related
stochastic variables and design of production and control equipment
are factors determining emissions.