PROPOSED REGULATORY LANGUAGE REVISIONS 

July 29, 2011 

API is continuing to address topics discussed during the May 26 and June 6, 2011 meetings with 

EPA. Two items are included here: 

1) Proposed definition of a “tight reservoir”; and 

2) Proposed regulatory language providing an approach to extrapolate flow-back 

volumes for gas well workovers and completions across a sub-basin category. 

Definition of “Tight Reservoir” 

API proposes the following definition to clarify the meaning of a “Tight Reservoir”: 

For Subpart W, a tight reservoir is an unconventional reservoir, excluding CBM and shale 

formations, that cannot be produced at economic flow rates or recover economic volumes of 

oil or natural gas unless the well is stimulated by a hydraulic fracture treatment. 

Flow-back Volume Normalization 

During the May 26, 2011 meeting, EPA had outlined an approach to extrapolate measured or 

quantified flow-back volumes for gas well completions and workovers across all workovers 

and completions in the sub-basin category. The following provides proposed mark-ups to the 

regulatory language to incorporate this approach. Our revisions for the flow-back volume 

normalization approach are indicated in blue text. These are added to the revisions 

addressing the sub-basin category approach provided to EPA on June 22, 2011, shown in red 

text. 

API’s revisions include a modification to Equation W-10 that consists of removing the 

subtraction of the SG term. API is proposing to define the “flow-back volume” term in 

Equation W-10 by limiting it only to the time span during which gas is actually vented to the 

atmosphere or flared. These proposed revisions add clarity, simplify the calculation, and 

reflect the emissions characteristics of flow-back operations. Without the removal of the SG 

term, Equation W-10 has the potential to either lead to the calculation of a negative emissions 

value, or compare emissions values vented to the atmosphere to sales values that are 

produced against the back-pressure of a gathering or sales pipeline; these are two completely 

different operating scenarios. 

Please note that these proposed regulatory revisions do not yet address changes to 

Methodology 2 under §98.233(g). API is working to develop an alternative approach to 

Equations W-11 and W-12, but this is a difficult technical challenge. API intends to address 

this separately with EPA. 
 

 

 

 

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(g) Gas well venting during completions and workovers 

from hydraulic fracturing. Calculate CH4, CO2 and N2O (when 

flared) annual emissions from gas well venting during 

completions involving hydraulic fracturing in wells and well 

workovers using Equation W-10 of this section. Both CH4 and 

CO2 volumetric and mass emissions shall be calculated from 

volumetric total gas emissions using calculations in 

paragraphs (u) and (v) of this section. 

Ea,n = (T*FR ∑Flow-back Volumewell) – EnF - SG (Eq. W-10) 

Where: 

Ea,n = Annual volumetric total gas emissions in cubic 

feet at standard conditions from gas well venting 

during completions and workovers following hydraulic

fracturing.

Flow-back VolumeWell = Volume of flow-back gas from

completions and workovers for the time that gas is

vented to the atmosphere or a flare, in cubic feet

at standard conditions from Equation W-YY 

T = Cumulative amount of time in hours of all well 

completion venting in a field during the year 

reporting. 

FR = Average flow rate in cubic feet per hour, under actual

conditions, converted to standard conditions, as 

required in paragraph (g)(1) of this section. 

EnF = Volume of CO2 or N2 injected gas in cubic feet at 

standard conditions that was injected into the 

reservoir during an energized fracture job. If 

the fracture process did not inject gas into the 

reservoir, then EnF is 0. If injected gas is CO2 

then EnF is 0.
 

SG = Volume of natural gas in cubic feet at standard

conditions that was recovered into a sales 

pipeline. If no gas was recovered for sales, SG 

is 0.
 

(1) The average flow rate for gas well venting to the 
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atmosphere or to a flare during well completions and 

workovers from hydraulic fracturing shall be determined 

using either of the calculation methodologies described in 

this paragraph (g)(1) of this section. 

(i) Calculation Methodology 1. For one horizontal 

well completion and one vertical well completion in each gas 

producing sub-basin category fieldand for one horizontal 

well workover and one vertical well workover in each gas 

producing sub-basin categoryfield, a recording flow meter 

(digital or analog) shall be installed on the vent line, 

ahead of a flare if used, to measure the backflow venting 

event according to methods set forth in §98.234(b). 

(A) The average flow rate in standard cubic feet per 

hour of venting to the atmosphere or routed to a flare is 

determined from the flow recording over the period of 

backflow venting to the atmosphere or a flare. 

(B) The respective average flow rates for the 

horizontal and vertical wells are used to determine a volume 

factor (VF) to be applied to all horizontal and vertical gas 

well completions, respectively, in the producing sub-basin 

category fieldand to all horizontal and vertical well 

workovers, respectively, in the gas producing sub-basin 

category for the total number of hours of venting to the 

atmosphere or a flare of each of these wells as described in 

paragraph (g)(2) of this section. 
 

 

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(C) New flow rates for completions and workovers are 

measured every other calendar year for each reporting gas 

producing sub-basin categoryfield and gas producing geologic 

horizon in each gas producing field starting in the first 

calendar year of data collection. 

(D) Calculate total volumetric flow rate at standard 

conditions using calculations in paragraph (t) of this 

section. 

(ii) Calculation Methodology 2. For one horizontal 

gas well completion and one vertical gas well completion 

in each gas producing sub-basin categoryfield and for one 

horizontal well workover and one vertical well workover in 

each gas producing sub-basin categoryfield, record the 

well flowing pressure upstream (and downstream in subsonic 

flow) of a well choke according to methods set forth in 

§98.234(b) to calculate intermittent well flow rate of gas 

during venting to the atmosphere or a flare. Calculate 

emissions using Equation W-11 of this section for subsonic 

flow or Equation W-12 of this section for sonic flow: 
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(A) The average flow rate in standard cubic feet per 

hour of venting to the atmosphere or flaring across the 

choke is calculated for one horizontal well completion and 

one vertical well completion in each gas producing sub-basin 
 

 

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categoryfield and for one horizontal well workover and one 

vertical well workover in each gas producing sub-basin 

categoryfield by averaging the gas flow rates during venting 

to the atmosphere or routing to a flare.

(B) The horizontal and vertical respective flow rates are 

used to determine a volume factor (VF) to be applied to all 

horizontal and vertical well completions, respectively in the 

gas producing sub-basin categoryfield and to all horizontal 

and vertical well workovers, respectively, in the gas 

producing sub-basin categoryfield for the total number of 

hours of venting to the atmosphere or a flare of each of 

these wells as described in paragraph (g)(2) of this 

section. 

(C) Average flow rates for horizontal and vertical gas 

well completions and for horizontal and vertical gas well 

workovers in each sub-basin categoryfield shall be calculated 

once every two years for each reporting gas producing field 

and geologic horizon in each gas producing field starting in 

the first calendar year of data collection. 

(D) Calculate total volumetric flow rate at standard 

conditions using calculations in paragraph (t) of this 

section. 

(2) The average flow rates per hour determined in 

paragraph (g)(1) above shall be used to determine a flowback volume factor (VF) as follows. 

(A) Determine the average production rate per 
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hour for the first calendar month after well completion 

or well workover operations have ended and the well has 

been routed to normal production for well(s) measured or 

calculated in paragraphs (g)(1) above and all well 

completions or workovers. For wells routed to normal 

production late in a calendar year this period can extend 

into the following calendar year. Calculate this average 

hourly production rate as follows: 

PR= (Total Production in standard cubic feet) /total 

hours of production in the first calendar month) 

If a well, measured or calculated in paragraph 

(g)(1), is not put on production for a calendar month 

following completion/workover and flow-back it cannot be 

used for determination of an emission factor and another 

well must be measured or calculated as detailed in 

paragraph (g)(1) and used for determination of a volume 

factor. 

(B) Calculate a flow-back volume factor (in scf 

flow-back rate/hr per scf of production rate per /hr) as 

follows: 

VFFlow-back= FR /PR (Equation W-XX) 

Where: 

VFFlow-back = Flow-back volume factor, 

dimensionless 

FR= Average flow back rate of gas vented to the 

atmosphere or a flare in standard cubic feet per hour as 

determined in paragraph (g)(1)of this section. 
 

 

 

 

 

 

 

 

 

 

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PR = Average production rate in standard cubic feet 

per hour as determined in paragraph (g)(2) of this 

section. 

(C) Apply the flow-back volume factor from Equation 

W-XX to all well completions in the gas producing subbasin category and to all well workovers in the gas 

producing sub-basin category to determine volume of 

flow-back gas from well flow-back post fracture 

stimulation. Calculate the flow-back volume for each 

well completion and workover as follows: 

Flow-back Volumewell = VFFlow-back*PRwell*HRwell 

(Equation W-YY) 

Where: 

Flow-back Volumewell = standard cubic feet of gas 

vented to the atmosphere or a flare resulting from 

flow-back for the subject well. 

VFFlow-back= The flow-back volume factor calculated 

in paragraph (g)(2)(B) of this section (Equation W-XX) 

PRwell= The hourly production volume, in standard 

cubic feet per hour for each well as calculated in 

paragraph (g)(2)(A) of this section. 

HRwell = Total hours the subject well was flowedback vented to the atmosphere or a flare post fracture 

stimulation before being routed to production. 

If production of a well is delayed and the first 

calendar month of production is not available then use 

the average hourly flow rate of recent wells in the 
 

 

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same field during the first calendar month. This 

average hourly flow rate shall be determined from 

company records or engineering estimates. 

(23) The volume of CO2 or N2 injected into the well 

reservoir during energized hydraulic fractures will be 

measured using an appropriate meter as described in 

98.234(b) or using receipts of gas purchases that are 

used for the energized fracture job. 

(i) Calculate gas volume at standard conditions using 

calculations in paragraph (t) of this section. 

(ii) [Reserved] 

(3) The volume of recovered completion or workover gas 

sent to a sales line will be measured using existing company 

records. If data does not exist on sales gas, then an 

appropriate meter as described in 98.234(b) may be used. 

(i) Calculate gas volume at standard conditions using 

calculations in paragraph (t) of this section. 

(ii) [Reserved] 

(4) Both CH4 and CO2 volumetric and mass emissions 

shall be calculated from volumetric total emissions using 

calculations in paragraphs (u) and (v) of this section. 

(5) Determine if the well completion or workover from 

hydraulic fracturing recovered gas with purpose designed 

equipment that separates saleable gas from the backflow, 

and sent this gas to a sales line (e.g. reduced emissions 

completion). 
 

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(i) Use the factor SG in Equation W-10 of this 

section, to adjust the emissions estimated in paragraphs 

(g)(1) through (g)(4) of this section by the magnitude of 

emissions captured using reduced emission completions as 

determined by engineering estimate based on best available 

data. 

(ii) [Reserved] 

(56) Calculate annual emissions from gas well venting 

during well completions and workovers from hydraulic 

fracturing to flares as follows: 

(i) Use the total gas well venting volume during well 

completions and workovers as determined in paragraph (g) of 

this section. 

(ii) Use the calculation methodology of flare stacks 

in paragraph (n) of this section to determine gas well 

venting during well completions and workovers using 

hydraulic fracturing emissions from the flare. This 

adjustment to emissions from completions using flaring 

versus completions without flaring accounts for the 

conversion of CH4 to CO2 in the flare.