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Final Report
Annex 1: Screening and Guided Measurement Protocol
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Screening and Guided Measurement Protocol
Authors: Dan Zimmerle, Tim Vaughn, Clay Bell, Colorado State University
Laurie Williams, Fort Lewis College
STATUS: Final
Special Note
The attached document is the protocol utilized for the study, and was developed prior to field campaign.
With the exception of grammatical corrections, the protocol is included intact as it was utilized for the
field study, with two exceptions:
1) Notes have been added where significant deviations from the field plan occurred during
operations. These are discussed in more details in the main body of the report.
2) Some information has been redacted to protect confidential data of the industry study partners.
1.0 Overview
This document provides an overview of the facility screening plan to guide facility level measurements at
natural gas production and gathering facilities in the RPSEA target basin. The overall goal of the RPSEA
project is to reconcile aircraft mass balance and facility-based emissions estimates at the facility and sub-
basin level. Separate measurement protocols will be utilized for each O&G sector included in the study –
transmission compressor facilities (downwind measurements only); Gathering facilities (onsite and
downwind measurements); distribution facilities (onsite measurements); distribution and gathering
pipelines (onsite measurements); and production (onsite and downwind measurements). The Production
Module: Measurement Protocol provides an overview of the methane emission measurement collection
and conduct of field teams. The specific objective of the facility screening is to:
Guide subsequent measurements in order to characterize both the “body” and “long tail”
emission distributions.
We shall achieve the project objective by making measurements of methane emissions on a number of
partner facilities using source level measurement techniques and downwind methods. A fundamental aspect
of the project is to pair the two measurement techniques at multiple sites, allowing a comparison of the
measurement techniques and, potentially, a better estimate of measurement uncertainty. To the greatest
extent possible, measurements will also be conducted contemporaneously with aircraft overflights to assess
the impact of the spatial and temporal alignment between facility-based ground-level measurements and
aircraft measurement and mass balance methods, including some aerial sampling at a facility level, if
possible. Each team in the group will operate, measure and consolidate results independently for each
facility measured, maintaining the independence of the paired measurements.
Measurement of production and gathering facilities will follow the Production Module: Measurement
Protocol and Booster and Gathering Module: Measurement Protocol respectively. Site selection will be
guided by facility level screening performed following this protocol. Screening is intended to quickly
provide an approximation of the rate of methane emissions from a production well pad or gathering facility
(compressor station) using the inversion plume method. Bottom-up measurement teams will then be
directed by the screening results during subsequent days, allowing an increased number of sites with higher
emissions rates to be measured in order to better characterize the “long tail” (or “fat tail”) of the distribution.
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An approximately equal number of measurements will be taken from the upper third and lower two thirds
of screened facilities allowing the “body” of the distribution to also be well characterized. The resulting
measurements will be weighted in the analysis to avoid over-representing the large sources and potential
bias in the results.
Note: During the field campaign, pre-screening proved unsuccessful due to the weather and road access
issues, and the screening process was discontinued after the first week. See main report.
2.0 Clustered Sampling and Site Identification
To facilitate screening, a clustered sampling method is adopted. Clustered sampling allows the teams to
focus in a smaller geographic area reducing driving time between sites in order to increase the total number
of samples. The clustered sampling approach will also improve the coordination between onsite and
downwind teams during contemporaneous measurement.
A unique RPSEA Pad ID and RPSEA Station ID have been assigned to each known production site and
gathering station in the study region in advance of the field campaign. The unique IDs will be used for
communication and coordination between teams. Two clusters are assigned to each week of the campaign
as shown in Table 2-1. Figure 2-1 shows the outline of the clusters overlaid on the study area. Facility
locations in the clusters assigned to each week are shown in Figure 2-2, Figure 2-3 and Figure 2-4.
Table 2-1: Selected production clusters
Week Cluster IDs
A B
1 1 3
2 10 11
3 14 17
Figure 2-1: Selected clusters for measurement campaign
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Figure 2-2: Cluster 1 (blue polygon) & 3 (red polygon) assigned to week one of campaign. Marker
style represents facility type: star paddles for gathering stations, push pins for production wells.
Marker color represents operator: red is non-partner, white and blue are partner facilities.
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Figure 2-3: Clusters 10 (blue polygon) & 11 (red polygon) assigned to week two of campaign.
Marker style represents facility type: star paddles for gathering stations, push pins for production
wells. Marker color represents operator: red is non-partner, white and blue are partner facilities.
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Figure 2-4: Clusters 14 (blue polygon) & 17 (red polygon) assigned to week two of campaign.
Marker style represents facility type: star paddles for gathering stations, push pins for production
wells. Marker color represents operator: red is non-partner, white and blue are partner facilities.
3.0 Weekly Schedule
Screening will be performed Monday each week and used to guide the measurements during subsequent
days as illustrated in .
Non-partner facilities which are encountered on the screening route may be screened. These facilities may
be included in guided sampling to be measured from public road access using the OTM33A downwind
method, however non-partner facilities will not be measured by on-site teams.
Table 3-1. Screening may be performed Tuesday if weather prohibits screening Monday. Three mobile
emissions laboratories will perform screening; one operated by the University of Wyoming and two
operated by Aerodyne Research, Inc. One team will screen <redacted, company ID> production and
gathering facilities within cluster A while a separate team screens <redacted, company ID> facilities in
cluster B. The third team will screen <redacted, company ID> facilities in both clusters A & B. A company
escort will accompany each screening team enabling site access during screening. Additional screening
may be performed from public roads on Saturday and/or Sunday, however site access will not be possible
as company escorts will not be available.
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While downwind teams are screening, onsite teams will perform unguided measurement of production and
gathering facilities within the clusters assigned that week. Site selection during unguided measurement is
described further in section 7.0.
After screening, onsite and downwind teams will perform guided measurement of production and gathering
facilities for the remainder of the week. Site selection during guided measurement is described further in
section 8.1. <Weekly schedule by company redacted to protect company confidentiality. Screening is
allocated to partner companies in proportion to the size of their operations in the basin>. An escort will
accompany each measurement team to provide site access. Measurements may be taken on Saturday if
weather prohibits measurement during one or more weekdays and an escort is available. Teams will
coordinate to maximize the number of facilities at which contemporaneous onsite and downwind
measurements are made during the guided sampling period. Contemporaneous measurements and
coordination are described further in section 8.2.
Non-partner facilities which are encountered on the screening route may be screened. These facilities may
be included in guided sampling to be measured from public road access using the OTM33A downwind
method, however non-partner facilities will not be measured by on-site teams.
Table 3-1: Screening and measurement schedule. Identification of companies engaged on each
day has been redacted.
Team Protocol Sun Mon Tues Wed Thu Fri Sat
Aerodyne
Research
Inc. 1
Screen/
Tracer -
Screen
Cluster A
Scheduled assignments for study teams based on
proportion of size of partner company operations
-
Aerodyne
Research
Inc. 2
Screen/
Tracer -
Screen
Clusters A&
B
-
University
of Wyoming
Screen/
OTM33A -
Screen
Cluster B -
AECOM 1 Onsite - Onsite
facility
Measurement
-
AECOM 2 Onsite - -
SWN
LDAR Onsite - -
4.0 Site Accessibility Grades and Screening Route Determination
In advance of the field campaign sites within a cluster will be graded based on the downwind accessibility.
Grades will be assessed for each site for different wind directions. A route will be selected during the
evening preceding screening. The specific route will be chosen based on the anticipated wind conditions.
The list of sites within the cluster will be ordered by the grade for the predicted wind conditions to determine
a screening route which takes advantage of sites with high accessibility grades. As the wind conditions
change throughout the day, the site list may be re-ordered and the route adjusted. Sites with the highest
grades for the wind conditions will be the primary screening targets, however if wind conditions allow the
plume to be seen at sites with lower grades encountered in-route between primary targets these sites may
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be included. The route will be selected to include all gathering facilities within the cluster with downwind
access.
5.0 Screening Method
Screening will use the “inversion plume” method (Yacovitch, et. al.) to determine an estimate of the rate of
methane emissions from production and gathering sites on the screening route. 95% upper and lower
confidence bounds will be provided in addition to the estimate for each site. The screening team is permitted
to perform multiple passes by a single facility to improve uncertainties, or if wind conditions change to
allow an improved estimate to be made. As production sites are screened, the screening team will generate
a list of screened facilities within a cluster including the RPSEA Cluster ID, RPSEA Pad ID, number of
wells, latitude and longitude, estimated emissions rate, and 95 % upper and lower confidence bounds as
illustrated in Table 5-1. Sites which are attempted and determined as a “zero” or “unscreened” facility will
be documented in the table as described in section 6.0. A separate list will be developed for gathering
sites during the screening process as illustrated in Table 5-2.
When possible, screening will be performed from public roads. If obstructions exist between sites and
public roads which prohibit measurement, screening may be performed on the well pad or from private
access roads provided the vehicle is located far enough from potential leak locations for dispersion to be
considered Gaussian.
Table 5-1: Example table of screened production pads
RP
SE
A C
luster ID
RP
SE
A P
ad ID
No
. of W
ells
Latitu
de
Lo
ng
itud
e
Estim
ated E
missio
ns
(SC
FM
)
95
% U
pp
er Bo
un
d
(SC
FM
)
95
% L
ow
er Bo
und
(SC
FM
)
Su
ccessfully
Screen
ed
Attem
pted
“Zero
”
Attem
pted
“Un
screened
”
IR V
erification
(Plu
me/ N
oP
lum
e)
1 Pad 1 X XX.XX XX.XX XX.XX XX.XX XX.XX Y X - No Plume
1 Pad 2 X XX.XX XX.XX XX.XX XX.XX XX.XX Y - - -
1 Pad 3 X XX.XX XX.XX XX.XX XX.XX XX.XX N - X Plume
…
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Table 5-2: Example table of screened gathering facilities
RP
SE
A C
luster ID
RP
SE
A S
tation
ID
No
. of C
om
presso
rs
Latitu
de
Lo
ng
itud
e
Estim
ated E
missio
ns
(SC
FM
)
95
% U
pp
er Bo
un
d
(SC
FM
)
95
% L
ow
er Bo
und
(SC
FM
)
Su
ccessfully
Screen
ed
Attem
pted
“Zero
”
Attem
pted
“Un
screened
”
IR V
erification
(Plu
me/ N
oP
lum
e)
1 Station 1 X XX.XX XX.XX XX.XX XX.XX XX.XX X X - No Plume
1 Station 2 X XX.XX XX.XX XX.XX XX.XX XX.XX - - X Plume
1 Station 3 X XX.XX XX.XX XX.XX XX.XX XX.XX X - - -
…
6.0 Facilities with Near Background Concentration
Distinguishing facilities with near zero emissions from missed plumes presents a challenge and could
potentially bias the sample. The sample could be biased high if sites are truly “zero” emitters but omitted
from the list of screened facilities because the plume is not encountered during screening. The site would
not be considered in the subsequent random sample collected by measurement teams. Conversely the
sample could be biased low if a “non-zero” site is included as a “zero” in the list of screened facilities when
the plume was not actually encountered. However, this site could be selected during the subsequent random
sample reducing the opportunity for bias. To minimize the opportunity for bias, sites will be distinguished
as “zero” or “unscreened” using the following rules.
A site is considered “unscreened” and will not be included in the list of screened facilities if an attempt is
made to screen the facility however the methane concentration is near background levels and the screening
team is uncertain if the plume would be encountered at their location due to wind conditions, distance, or
obstructions between the site and screening vehicle.
A site may be considered screened successfully and included in the list of screened facilities as “zero” if
the concentration is near background, the screening vehicle is located directly downwind of the site, and
the space between the site and screening vehicle is free of obstructions. In this case only an upper limit
will be reported.
Additionally it is possible for the screening team to be located too close to a facility for the dispersion to be
considered Gaussian, in which case the inversion plume method would result in an estimate biased high.
In this case the facility will be considered “unscreened” if the screening team cannot repeat the measurement
further downwind.
In all cases the screening team will note that the site was visited and whether it was considered “unscreened”
or “zero”. When possible, the screening team will verify whether or not the plume is missed using an
optical gas imaging camera to ensure zero sites are not being mislabeled as “unscreened” potentially
resulting in a biased sample.
7.0 Coordination with Measurement Teams during Screening
Screening teams may not be able to start early in the morning before winds have developed. As a result,
onsite teams may be dispatched first as illustrated in Table 7-1. Onsite teams will be vectored to sites which
have a high probability of being screened as determined by the study coordination team using predicted
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wind directions and the routes proposed by the screening teams (Sites Gath A, Prod A-D in Table 7-1 are
selected this way). If screening had been performed from public roads on the Sunday prior, successfully
screened sites will be selected. In the afternoon onsite teams are vectored to <redacted, company ID> sites
which have been screened by ARI or UWyo. (Sites Gath B, Prod E-H in Table 7-1 are selected this way).
During screening no paired measurements are made.
Table 7-1: Coordination with measurement teams during screening
Time of Day 7 8 9 10 11 12 1 2 3 4 5
ARI 1 - - Screening
ARI 2 - - Screening
UWyo - - Screening
AECOM 1 Gath Site A - Gath Site B -
AECOM 2 - Prod Site A Prod Site C - Prod Site E Prod Site G -
SWN LDAR - Prod Site B Prod Site D - Prod Site F Prod Site H -
8.0 Analysis of Screening Results and Guided Measurement
Following the screening an evening “all hands” meeting will be held. The purpose of the meeting will be
to review screening results, perform site selection for subsequent measurements within the clusters, and
coordinate contemporaneous measurement of facilities. The meeting will be led by the CSU Coordination
Team. Prior to the meeting screening teams will provide the list of screened facilities in the form of Table
5-1and Table 5-2 to the Coordination Team. The onsite teams will provide a list of facilities measured
during un-guided measurement. Site selection will be made for the remaining samples within the clusters
as described in section 8.1.
8.1 Site Selection for Guided Measurement
The lists generated during screening will be combined to include screened facilities operated by both partner
companies, SWN and XTO Energy. One list will be generated for production and one list for gathering for
each cluster. Each cluster will then be sorted by the magnitude of the emissions estimate from screening.
The upper one third and lower two thirds of the list will be identified. Routes will then be selected for each
measurement team for each remaining sampling day. Daily routes may consider sites in both clusters
assigned to the week, provided the expected number of sites covered in each cluster is approximately equal
at the end of the week. The priority for selecting routes is:
1. Contain approximately equal number of sites from the upper third and lower two thirds of
screened sites;
2. Overlap downwind and onsite teams to maximize contemporaneous measurements.
3. Contain alternate sites in case wind conditions, access issues, or safety prevent
measurement of facilities earlier on the list.
4. Consider geography to reduce transit time between sites;
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At the discretion of the CSU Coordination Team measurement teams may be re-routed in order to obtain
improved coverage within each cluster, balance the number of samples from the upper third and the lower
two-thirds of screened facilities, or improve the coordination of contemporaneous measurements.
Each evening the study team will host a similar meeting at which the route and sampling targets for the
next day will be reviewed and updated.
8.2 Contemporaneous Measurements
Onsite and downwind measurements taken at a facility on the same day will be considered
contemporaneous provided no significant changes in equipment states occur between. The company escort
will assist the measurement team (onsite or downwind) to record the equipment states during their
measurement. Equipment states during onsite and downwind measurement of each facility will be
compared to determine if the operational configuration is the same and the measurements may be
considered contemporaneous.
Coordination between the onsite and downwind teams at production facilities is illustrated in Table 8-1 and
at gathering facilities in Table 8-2 and Table 8-3. In order to maximize contemporaneous measurements
the sites in the route developed in section 8.1 may be visited out of order by one or more teams. The CSU
observer will act as the liaison between teams and coordinate contemporaneous measurements. This will
require the teams be operating nearby and some flexibility in the daily schedule.
Table 8-1: Coordination of onsite and downwind teams for contemporaneous measurement of
production facilities
Time of Day 7 8 9 10 11 12 1 2 3 4 5
UWyo (OTM33A) - - Site 2 Site 1 - Site 5 - Site 6 -
AECOM (Onsite) - Site 1 Site 2 - Site 3
SWN (LDAR) - Site 4 - Site 5 - Site 6 - -
Table 8-2: Coordination of onsite and downwind teams for contemporaneous measurement of
large gathering facilities
Time of Day 7 8 9 10 11 12 1 2 3 4 5
ARI (Dual Tracer) - - - Site 1 Site 2 -
AECOM (Onsite) - Site 1 -
Table 8-3: Coordination of onsite and downwind teams for contemporaneous measurement of
small gathering facilities
Time of Day 7 8 9 10 11 12 1 2 3 4 5
ARI (Dual Tracer) - - - Site 1 Site 2 Site 3 -
AECOM (Onsite) - Site 1 - Site 2 -
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9.0 References
Mobile Laboratory Observations of Methane Emissions in the Barnett Shale Region Tara I. Yacovitch,
Scott C. Herndon, Gabrielle Pétron, Jonathan Kofler, David Lyon, Mark S. Zahniser, and Charles E.
Kolb Environmental Science & Technology 2015 49 (13), 7889-7895 DOI: 10.1021/es506352j