Bakken Pool 

Oil and Gas Production Facilities

Air Pollution Control

Permitting & Compliance Guidance

North Dakota Department of Health

Division of Air Quality

Effective Date May 2, 2011
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Table of Contents

1. ACRONYMS AND ABBREVIATIONS 4

2. BACKGROUND

A. Introduction 5

B. Unique Issues with Bakken Pool VOCs 6

C. Applicability 6

D. Potential to Emit Action Levels 7

E. Registration Only 8

F. Permit to Construct and Title V Operating Permit (Major Source) 8

G. Prevention of Significant Deterioration (PSD) 9

H. Potential to Emit 9

I. New Source Performance Standards (NSPS) and Maximum 

Achievable Control Technology (MACT) Applicability 9

J. Regulated Air Pollutant Sources 9

K. Control of Bakken Pool O&G Production Facility VOC Emissions 10

L. Greenhouse Gas Emissions 10

M. Multiple Well Pad Statement 10

3. FORM COMPLETION

A. Oil & Gas Facility Registration Process 10

B. Emission Calculation Workbook 11

C. Emission Calculation Workbook Instructions 11

4. EMISSION SOURCE DETAILS

A. Oil/Condensate Tanks 17

B. Calculating Tank Emissions 17

C. Bakken Pool Tank Vapor Emission Factor 17

D. Tank Emissions Control Threshold 18

E. Tank Emissions Control Requirements 18

F. Produced Water Tanks 18

G. Glycol Dehydrators 18

H. Calculating Glycol Dehydrator Emissions 18

I. Glycol Dehydrator Control Threshold 18

J. Glycol Dehydrator Control Requirements 18

K. Glycol Dehydrator Federal Regulations 19

L. Calculating Treater Gas Flare Emissions 19

M. Control Requirements for Treater Gas 20

N. Natural Gas Fired Heaters & Burners 20

O. Truck Loading 20

P. Truck Loading Control Requirements 21

Q. Reciprocating Internal Combustion Engines (RICE) 21

R. RICE Control Requirements 22

S. Federal Regulations for RICE 22

T. Pneumatic Pumps 22
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U. Pneumatic Pump Control Requirements 22

V. Pneumatic Controllers 23

W. Pneumatic Controller Control Requirements 23

5. EFFECTIVE DATE 23

APPENDICES

Appendix A – Oil & Gas Production Facility Registration Form 24

Appendix B – Oil & Gas Production Facility 

Emission Calculation Workbook Screenshots 27

Appendix C- NDDoH Acceptable Control Systems or Devices 38

Appendix D- Control Requirements for Tank Emissions 40

Appendix E – The Basis for the 0.6 Decline Factor 41
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1. ACRONYMS AND ABBREVIATIONS

AP-42 EPA Publication AP-42, Compilation of Air Pollutant Emission Factors (5th Edition)

Bakken Pool Oil from Bakken, Three Forks, and Sanish Formations

bbl barrel 

BOPD barrels of oil per day 

BTEX benzene/toluene/ethyl-benzene/xylenes 

Btu British thermal unit 

Btu/hr Btu per hour

CO carbon monoxide 

DRE destruction and removal efficiency

EF emission factor

EPA Environmental Protection Agency 

gpm gallons per minute 

H2S hydrogen sulfide 

HAP hazardous air pollutants 

hp horsepower 

lb pound 

lb/lb-mole pound per pound mole

LACT Lease Automatic Custody Transfer

MMBtu one million Btu

MMscf one million standard cubic feet (scf × 106) 

MMscfd = 1,000,000 scf per day 

Mscf one thousand standard cubic feet (scf × 1000) 

Mscfd = 1000 SCF per day

NDDoH North Dakota Department of Health

NESHAP National Emission Standards for Hazardous Air Pollutants 

NOx nitrogen oxides 

NSCR Non-Selective Catalytic Reduction

NSPS New Source Performance Standards 

O&G Oil and Gas

PSD Prevention of Significant Deterioration 

psig pounds per square inch gauge 

psia pounds per square inch absolute

PTE potential to emit

RICE reciprocating internal combustion engine

scf standard cubic foot 

scf/bbl standard cubic foot per barrel

SO2 sulfur dioxide 

S/W/B standing/working/breathing losses 

TEG tri-ethylene glycol 

Title V Title V of the Clean Air Act Amendments of 1990

TOC total organic compounds

TPY tons per year 

VOC volatile organic compounds
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2. BACKGROUND

A. Introduction

The creation of this guidance document (Guidance) was a coordinated effort between the North 

Dakota Department of Health (NDDoH) and the Bakken VOC Task Force, which is comprised 

of an Emission Factor Committee and an Emission Control Committee.

This Guidance provides an approach that may be used by Bakken Pool Oil and Gas (O&G)

production facility owners/operators to demonstrate compliance with the applicable North 

Dakota Air Pollution Control Rules (including, but not limited to the requirements established by 

Chapters 33-15-07 and 33-15-20, N.D. Admin. Code). This Guidance provides owners and 

operators of Bakken Pool O&G production facilities that have the potential to emit air pollutants 

below the major source thresholds (minor Bakken Pool O&G production facilities) with an 

alternative to obtaining North Dakota air pollution control permits. Owners and operators of 

minor Bakken Pool O&G production facilities may still choose to apply for facility-specific air 

pollution control permits. The NDDoH will consider those applications on a case-by-case basis.

It should be noted that emissions associated with the exploration and production of O&G

resources cannot be predicted with any degree of precision or accuracy until after it is 

determined the oil or gas well will actually produce and site specific production data are 

collected and known. Therefore, unlike other stationary sources for which projected emissions 

upon startup can be estimated in advance for purposes of pre-construction air permitting, 

emissions from O&G exploration and production facilities are only known post-construction and

completion. This situation is unique to O&G exploration and production facilities and, therefore, 

requires a practical regulatory response. To accommodate this reality, the NDDoH has tailored 

its O&G registration process and this Guidance to allow for the start-up of new exploration and

production facilities, and the modification of existing facilities, to occur prior to requiring the 

submittal of the appropriate O&G Registration Packet, provided the owners/operators of such 

facilities meet certain emission control requirements that have been established within this 

Guidance document. This represents a rational and practical regulatory response to operational 

realities posed by O&G exploration and production operations.

Control requirements have been established within this Guidance for tank emissions and 

emissions from dehydration units, treater flares and pneumatic pumps. Emissions from other 

sources such as pneumatic controllers, truck loading, etc. are also included in this Guidance.

Nothing in this Guidance is intended to relieve owners and operators of Bakken Pool O&G

production facilities of the responsibility to comply with all State and Federal environmental 

laws and rules. Owners and operators of Bakken Pool O&G production facilities with the 

potential to emit at or above major source thresholds must follow the normal permitting 

processes established in Chapters 33-15-14 and 33-15-15 of the North Dakota Air Pollution 

Control Rules.
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B. Unique Issues with Bakken Pool VOCs

Crude oil from the Bakken Pool (defined as wells in the Bakken, Sanish and Three Forks 

formations) typically contains a high amount of lighter end components which have the potential 

to produce increased volumes of flash emissions. Because of this, customary correlations such as 

API’s E&P Tanks and Vasquez-Beggs do not work well for estimating flash vapors in the 

Bakken, potentially overestimating and underestimating emissions.

Recognizing the need to predict tank emissions at Bakken Pool O&G production facilities, the 

NDDoH and industry collaborated and formed the Bakken VOC Task Force. The Task Force 

included the Emission Factor Committee and the Emission Control Committee.

The Emission Factor Committee’s goal was to gather direct measurement data collected by 

various owners/operators within the Bakken Pool and establish an emission factor that could be 

used to predict tank emissions from producing Bakken Pool formation wells.

The Emission Control Committee’s goal was to evaluate available emission control technologies

and to recommend the best emission control for different emission scenarios.

The findings of both Committees were used as a platform to create this Guidance for Bakken 

Pool O&G production facilities. The data from the Bakken VOC Task Force that was used to 

create the default values for Bakken Pool O&G production facilities were submitted and revised 

by NDDoH and are available for public review upon request. Use of the Bakken default values

to calculate VOC emissions is expected to result in a conservatively high estimate of VOC 

emissions. As an alternative to using the Bakken default values, site-specific data can be used to 

estimate emissions. In the vast majority of cases, the use of site-specific data instead of the 

Bakken default values is expected to result in lower calculated VOC emissions.

As mentioned above, Bakken Pool O&G production facilities are different from other O&G 

production facilities in North Dakota because of the higher potential for flash emissions. This 

Guidance was created to provide a consistent and more accurate approach for calculating 

emissions from the Bakken Pool O&G production facilities. While all producing wells in the 

State will need to have a registration form filed with NDDoH (see Appendix A) and emissions

calculations performed, it is not expected that non-Bakken Pool O&G production facilities will 

require emission controls for tank emissions to the same extent as Bakken Pool production 

facilities. 

Although the Guidance is applicable to Bakken Pool O&G production facilities, the Emission 

Calculation Workbook may also be used for non-Bakken Pool O&G production facilities; 

however, it should be noted that some of the default values in the Workbook are specific to 

Bakken Pool O&G production facilities. When applying the Workbook to non-Bakken Pool 

O&G production facilities, the user should review the Workbook to ensure that the values are 

appropriate for the production facility being evaluated. 
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C. Applicability

All Bakken Pool O&G production facilities (excluding those facilities on Tribal Land) within the 

State of North Dakota that emit regulated air contaminants into the atmosphere are subject to the 

requirements discussed in this Guidance and are required to submit either a new or an updated

O&G registration packet to NDDoH.

Each Bakken Pool O&G production facility owner or operator will receive a letter detailing 

instructions on well information submissions. The following summarizes the content of the 

submissions.

Existing Bakken Pool O&G production facilities are those where the first date of production 

occurred on or before June 1, 2011. Owners/operators that have previously submitted 

registration forms will be required to submit the worksheet detailing well information such as 

controls, calculations and dates. The NDDoH will supply a blank worksheet to perform the 

calculations that contains all required fields. Each owner/operator must submit the spreadsheet 

information to the NDDoH by December 1, 2011 (note that the worksheet is in lieu of a new 

registration).

All owners/operators of existing Bakken Pool O&G production facilities that have not previously 

filed a registration form must submit a new registration packet to NDDoH by no later December

1, 2011 or within 90 days after the first date of production, whichever is later. These registrations 

will include information on each well, including all prior controls, in the worksheet (supplied by 

the NDDoH).

New Bakken Pool production facilities are those where the first date of production occurs after 

June 1, 2011. The owner/operator of a new Bakken Pool O&G production facility must submit a 

registration packet to NDDoH within 90 days after the first date of production.

D. Potential to Emit (PTE) Action Levels

Based on the total facility-wide emissions, there are three different registration/permit action 

levels that will require varying submittals for Bakken Pool O&G production facilities, regardless 

of location. All new and previously unregistered Bakken Pool O&G production facilities must 

register with the NDDoH as provided in the Applicability section above. The owner/operator of 

previously registered Bakken Pool O&G production facilities need only submit a summary 

spreadsheet as outlined in the Applicability section above. The flowchart below can be used to 

determine the action/actions an owner/operator needs to take depending on the potential to emit 

of the Bakken Pool O&G production facility.
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Action Flowchart

E. Registration Only

If a Bakken Pool O&G production facility has a potential to emit (PTE) <100 TPY of any criteria 

pollutant, <25 TPY of combined HAP and <10 TPY of any single HAP, the owner/operator only 

needs to submit a completed registration packet for that facility within 90 days after the first date 

of production for new production facilities or by December 1, 2011 (whichever is later). No 

further action is required. See example forms in Appendices A and B.

F. Permit to Construct and Title V Operating Permit (Major Source)

If a Bakken Pool O&G production facility has a PTE >100 TPY of any criteria pollutant, >25 

TPY of combined HAP or >10 TPY of a single HAP, the facility is required to obtain a Permit to 

Construct and a Title V permit as required by Chapter 33-15-14. Although the O&G production 

facility is subject to permitting requirements, a registration packet is still required to be 

submitted within 90 days after the first date of production. These permitting requirements are 

beyond the scope of this Guidance, but more information on the permitting process can be 

obtained from the NDDoH website at: http://www.ndhealth.gov/AQ/AirPermitting.htm.

VOC, CO, NOx 

<100 TPY &

Combined HAP 

<25 TPY & Single 

HAP <10 TPY

 Submit 

Registration 

Packet within 90 

days after the first 

date of production 

(new well) or by 

12/1/11 (for 

existing wells)

 No further action

VOC, CO, NOx 

>100 TPY or

Combined HAP 

>25 TPY or Single 

HAP >10 TPY

 Submit 

Registration 

Packet within 90 

days after the first 

date of production 

(new well) or by 

12/1/11 (for 

existing wells)

 A Permit to 

Construct is 

required

 Submit Title V 

Application 

within 365 days

of the first date of 

production

VOC, CO, NOx 

>250 TPY

 Requires a PSD 

Application and 

Permit

 PSD is a preconstruction 

permit

 Contact the 

NDDoH for 

further guidance
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G. Prevention of Significant Deterioration (PSD)

A Bakken Pool O&G production facility that either emits, or has the PTE, >250 tons per year of 

any air contaminant regulated under North Dakota Century Code Chapter 23-25 (or >100,000 

tons per year of greenhouse gases), as determined by the NDDoH, must comply with the 

permitting requirements of Chapter 33-15-15 (Prevention of Significant Deterioration of Air 

Quality).

The PSD permit is a pre-construction permit. A facility cannot construct until a permit 

application has been filed and the permit has been issued. The PSD permitting process is a 

complicated, time-consuming process that is beyond the scope of this Guidance. More 

information on the PSD permitting process can be obtained from the NDDoH website at: 

http://www.ndhealth.gov/AQ/AirPermitting.htm.

H. Potential to Emit

The federal regulations define "potential to emit" as: “The maximum capacity of a stationary 

source to emit a pollutant under its physical and operational design. Any physical or operational 

limitation on the capacity of the source to emit a pollutant, including air pollution control 

equipment and restrictions on hours of operation or on the type or amount of fuel combusted, 

stored or processed, shall be treated as part of its design if the limitation or the effect it would 

have on emissions is federally enforceable.”

Chapter 33-15-07 of the North Dakota Air Pollution Control Rules states, “No person may cause 

or permit the emission of organic compounds gases, vapors.....unless these gases and vapors are 

burned by flares or an equally effective control device as approved by the Department. Chapter 

33-15-07 has been approved by the EPA as part of the North Dakota State Implementation Plan 

and as a result, is federally enforceable. Therefore, for an oil and gas production facility, the

PTE of VOCs and the associated HAPs is calculated post-controls. Please refer to Appendix C 

for approved control devices. This Guidance is intended to assist O&G owners/operators

demonstrate compliance with Chapter 33-15-07.

I. New Source Performance Standards (NSPS) and Maximum Available Control 

Technology (MACT) Applicability 

Equipment at Bakken Pool O&G production facilities may be subject to rules and regulations 

under 40 CFR Parts 60 and 63. These federal regulations are beyond the scope of this document. 

It is the owner/operator’s responsibility to determine if equipment is subject to these federal 

regulations. A summary of numerous Federal rules that may apply to Bakken Pool O&G

production facilities is located at: www.ndhealth.gov/AQ/OilAndGasWells.htm.
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J. Regulated Air Pollutant Sources 

When registering a Bakken Pool O&G production facility, all emission sources at that particular 

facility must be considered to determine source status (major or minor source). Generally, the 

following are the most common emission sources and the type of regulated air pollutants they 

may emit at a typical Bakken Pool O&G production facility:

 Oil/Condensate Tanks – VOC, HAP, H2S (NOx, CO, SO2 when controlled)

 Produced Water Tanks – VOC, HAP, H2S (NOx, CO, SO2 when controlled)

 Treater Flares – VOC, HAP, NOx, CO, H2S, SO2

 Heaters/Burners – VOC, HAP, NOx, CO, SO2

 Truck Loading – VOC, HAP

 RICE Engines – VOC, HAP, NOx, CO

 Pneumatic Pumps – VOC, HAP

 Pneumatic Controllers – VOC, HAP

 Fugitives – VOC, HAP

K. Control of Bakken Pool O&G Production Facility VOC Emissions

Based on historical information from Bakken Pool O&G production facilities, flashing emissions 

from the production tanks may be significant. Acceptable VOC emission control systems or 

devices are discussed in Appendix C. The control requirements for emissions from production 

tanks are outlined in Appendix D of this document.

L. Greenhouse Gas (GHG) Emissions

It is the responsibility of each owner/operator to determine the applicability of GHG emissions 

inventory reporting and permitting rules to their facilities and to comply with the rules. If 

multiple wells are drilled from a single pad, GHG emissions from all wells may need to be 

aggregated (see Multi Well Pad Statement below).

M. Multi Well Pad Statement

When multiple wells are drilled from a single pad, it may be necessary to aggregate all emission 

sources at the multiple well production facility and additional permitting requirements may apply 

(Title V, PSD, etc.), which are beyond the scope of this document. Questions regarding 

permitting requirements for multi-well production facilities should be addressed to Craig 

Thorstenson of the Division of Air Quality at 701-328-5188 or cthorstenson@nd.gov. 

3. FORM COMPLETION

A. Oil & Gas Facility Registration Process

Within 90 days after the first date of production or recompletion of any Bakken Pool O&G

production facility, the following documents (registration packet) must be submitted to the 

NDDoH for the facility:
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Registration Packet Contents

1) A completed Oil/Gas Registration Form (AP-114)

2) A gas analysis of any gas produced from the well

3) The first 2 pages (Input and Emission Summary) of a completed Oil and Gas Facility 

Emission Calculation Workbook

The Registration packet, (forms and examples found at: 

http://www.ndhealth.gov/AQ/OilAndGasWells.htm), which includes the above three items, must 

be sent to the following address:

North Dakota Department of Health

Division of Air Quality

918 E Divide Ave, 2nd Floor

Bismarck, ND 58501-1947

B. Emission Calculation Workbook

The Emission Calculation Workbook can be downloaded from the NDDoH O&G website in 

Excel format. The workbook will serve two functions: it will provide a simple way of calculating 

facility-wide emissions, as well as insuring that all owner/operators are calculating emissions in a 

consistent manner that meets the requirements of NDDoH.

The Oil & Gas Facility Emission Calculation Workbook contains the following 10 tabs:

 Input – The necessary data to perform the required calculations are entered here

(required to be submitted in Registration Packet).

 RICE Input – The necessary data to perform the required calculations for RICE are 

entered here (required to be submitted in Registration Packet).

 Emission Summary – The calculated emissions are summarized by source and pollutant

here (required to be submitted in Registration Packet).

 Oil/Condensate Tanks – The tank vapor emissions are calculated here.

 Treater Flare – The treater flare emissions are calculated here.

 Treater Burner – The treater burner emissions are calculated here.

 Truck Loading – The truck loading emissions are calculated here.

 RICE – The RICE emissions are calculated here.

 Pneumatic Pump – The pneumatic pump emissions are calculated here.

 Pneumatic Controllers –The pneumatic controller emissions are calculated here.

C. Emission Calculation Workbook Instructions

The Emission Calculation Workbook can be completed in three steps: Calculating production 

numbers, calculating glycol dehydrator emissions using GRI-GLYCalc (if applicable) and 

entering data into the Emission Calculation Workbook.
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Step 1

Thirty days after the first date of production or recompletion of a Bakken Pool O&G production 

facility, the average daily production for the facility needs to be calculated. Once calculated, this 

production data will need to be entered into the Emission Calculation Workbook in order to 

perform the required emission calculations.

Step 2

If the facility has a glycol dehydrator in operation, the NDDoH recommends using GRIGLYCalc V4 or higher to calculate the emissions. Other programs may be used upon approval 

from the NDDoH.

Step 3

Complete the entire Emission Calculation Workbook per the detailed instructions below:

Data Input

Facility and Registration Information: Lines 1-3

Line 1: Enter the name of the facility and the well number.

Line 2: Enter the first date of production or date of recompletion of the facility.

Line 3: Enter the date that the registration packet is submitted to the NDDoH.

Production Data: Lines 4-8

Line 4: New wells: enter the average daily production in BOPD, based on the first 30 days of 

production, excluding any days the well was not operating during that period of time. Existing 

wells: enter the average daily production in BOPD, based on the most recent 30 days of 

production, excluding any days the well was not operating during that period of time.

Line 5: New wells: enter the average daily production of gas in Mscf per day, based on the first 

30 days of production, excluding any days the well was not operating during that period of time.

Existing wells: enter the average daily production in Mscf, based on the most recent 30 days of 

production, excluding any days the well was not operating during that period of time.

Line 6: New wells: enter 0.6 on this line. This equates to an 80% decline in production from the 

well during the first year of production. If the expected decline rate is less than 80%, then the 

expected decline rate should be used. Existing wells: in most situations, a decline factor may not 

be used for an existing well; therefore, enter 1 on this line. The Department will accept a decline 

factor other than 0.6 or 1 in the following instance: an actual decline factor (based on well 

production) must be submitted for each well that is producing for less than one year before June 

1, 2011. Wells that have produced for more than one year before June 1, 2011 must use a 

decline factor of 1. See Appendix E for an explanation of the decline factor and how it relates to 

an 80% decline in production during the first year of production.
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Line 7: No input required. This is the projected first year average daily oil production rate 

(BOPD). This is automatically calculated by multiplying the average daily rate entered on Line 3

by the decline factor entered on Line 5.

Line 8: No input required. This is the projected first year average daily gas production rate 

(Mscfd). This is automatically calculated by multiplying the average daily rate entered on Line 4, 

by the decline factor entered on Line 5.

Oil/Condensate Tank Data: Lines 9-19

Line 9: Using the drop down box, select the appropriate flash gas method used for determining 

the tank vapor emission factor (scf/bbl).

 Default Bakken EF

 Site Specific Direct Measurement

 Representative Average (This average can be established from direct measurements from 

a minimum of six different wells within the same field and operating under similar 

parameters; however, it requires a case-by-case review and approval by the NDDoH prior 

to submitting the registration packet).

Line 10: Enter the scf/bbl EF based on the method chosen on Line 8.

 Default Bakken EF: If site specific data is not available, the default Bakken EF of 97.91 

scf/bbl should be used.

 Direct Measurement: If site specific direct measurements have been taken, enter the 

measured scf/bbl EF determined from taking the direct measurement.

 Representative average: Enter the representative average scf/bbl approved by the 

NDDoH.

Line 11: No input required. This is a calculated value determined by multiplying the adjusted 

BOPD value on Line 6, by the scf/bbl entered in Line 9.

Line 12: Enter the lower heating value (Btu/scf) of tank vapors. If site specific data is not 

available, use the Bakken default value of 2000.

Line 13: Enter the molecular weight of the tank vapors in pounds per pound-mole (lb/lb-mole). 

If site specific data is not available, use the Bakken default value of 45.19.

Line 14: Enter the VOC weight fraction of the tank vapor gas (C3+). If site specific data is not 

available, use the Bakken default value of 79.8%.

Line 15: Enter the HAP weight fraction of the tank vapor gas. If site specific data is not 

available, use the Bakken default value of 2.26%. A complete list of HAPs is located at 

http://www.epa.gov/ttn/atw/orig189.html.

Line 16: Enter the H2S weight percent of the tank vapors.
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Line 17: Enter the H2S mole percent of the tank vapors.

Line 18: Use the drop down menu to select the type of device used to destruct tank vapors from 

the following options:

 Vapor Recovery Unit or Oil Stabilizer

 Enclosed Smokeless Combustor

 Utility Flare or Other 98% DRE Device

 Ground Pit Flare or other 90% DRE device

Line 19: No input required. This is a fixed destruction efficiency based on the control type 

selected on Line 17.

 Vapor Recovery Unit or Oil Stabilizer = 99% DRE

 Enclosed Smokeless Combustor = 98% DRE

 Utility Flare or Other 98% DRE Device = 98% DRE

 Ground Pit Flare or other 90% DRE device = 90% DRE

Treater Gas Data: Lines 20-29

Line 20: Enter the site specific Btu/scf of the wellstream gas. 

Line 21: Enter the average molecular weight of the wellstream gas in lb/lb-mole. 

Line 22: If it is necessary to convert specific gravity to molecular weight, enter the specific 

gravity of the wellstream gas.

Line 23: This is the calculated molecular weight of the wellstream gas based on the specific 

gravity entered on Line 22. Enter this value on Line 21.

Line 24: Enter the VOC weight fraction of the wellstream gas (C3+). Note that this is the 

weight percent, not the mole percent of the gas.

Line 25: Enter the HAP weight fraction of the wellstream gas. Note that this is the weight 

percent, not the mole percent of the gas. A complete list of HAPs is located at 

http://www.epa.gov/ttn/atw/orig189.html. 

Line 26: Enter the H2S weight percent of the wellstream gas.

Line 27: Enter the H2S mole percent of the wellstream gas.

Line 28: Use the drop down menu to select the type of device used to destruct the wellstream gas 

from the following options:

 Enclosed Smokeless Combustor

 Utility Flare or other 98% DRE Device
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 Ground Pit Flare or other 90% DRE device

 Connected to Sales Line

Line 29: No input required. This is a fixed destruction efficiency based on the control type 

selected on Line 25.

 Enclosed Smokeless Combustor = 98% DRE

 Utility Flare or Other 98% DRE Device = 98% DRE

 Ground Pit Flare or other 90% DRE device = 90% DRE

 Connected to Sales Line = 100% DRE

Treater Burner(s) Data: Lines 30-31

Line 30: Enter the total burner rating for the treater burner(s) in Btu/hr. If there are multiple 

burners at the facility, enter the total heat input of all burners.

Line 31: The burner(s) is/are assumed to operate 8,760 hours per year. 

Truck Loading Data: Lines 32-38

Line 32: Use the drop down menu to choose the appropriate oil sales method. If oil is sold 

through a Lease Automatic Custody Transfer, no input values are required in Lines 30-35.

Line 33: Use the drop down list to choose the appropriate mode of operation. The saturation 

factor will automatically be selected based on mode of operation.

Line 34: Enter the molecular weight of tank vapors, lb/lb-mole. If no site specific data is 

available, please refer to Table 2 on the Truck Loading tab.

Line 35: Enter the true vapor pressure of liquid loaded, pounds per square inch absolute (psia).

If no site specific data is available, please refer to Table 2 on the Truck Loading tab.

Line 36: Temperature of bulk liquid loaded in degrees Fahrenheit. If no site specific data is 

available, use an estimated average annual temperature.

Line 37: Enter the load rate of liquid loaded in barrels per hour.

Line 38: Enter the time (in hours) it takes to loadout one load.

Pneumatic Pumps Data: Lines 39-43

Line 39: Enter the number of pneumatic pumps at the facility.

Line 40: Enter the hours each pump is in operation annually. For winter months only, enter 4380 

hours.

Line 41: Enter the pneumatic source consumption rate from manufacturer’s data (scf/min).
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Line 42: Use the drop down menu to choose the appropriate emission control type.

Line 43: No input required. Control efficiency is automatically calculated based on control type 

selected on Line 55.

Pneumatic Controllers Data: Lines 44-45

Line 44: Enter the number of pneumatic controllers at facility.

Line 45: Enter the average bleed rate of device (scf/hr).

Glycol Dehydrator Data: Lines 46-47

Line 46: Enter the TPY of VOC emissions calculated in GRI-GLYCalc V4 software. (If no 

glycol 

dehydrator is installed, enter 0).

Line 47: Enter the TPY of HAP emissions calculated in GRI-GLYCalc V4 software. (If no 

glycol dehydrator is installed, enter 0).

RICE Data Input: Lines 1-97

Line 1: Enter the number of engines to be installed at the production facility.

RICE Engine #1: Lines 2-9

Line 2: Engine is assumed to operate 8,760 hours per year.

Line 3: Enter the manufacturer’s maximum hp rating.

Line 4: Enter the manufacturer's emission factor, actual test results or AP-42 factor in grams per 

horsepower hour (g/hp-hr) for nitrogen oxides (NOx).

Line 5: Enter the manufacturer's emission factor, actual test results or AP-42 factor in g/hp-hr

for carbon monoxide (CO).

Line 6: Enter the manufacturer's emission factor, actual test results or AP-42 factor in g/hp-hr

for volatile organic compounds (VOC).

Line 7: Enter the NOx control efficiency of any applicable controls (NSCR catalyst, AFRC, etc.)

obtained from manufacturer data or actual test results.

Line 8: Enter the CO control efficiency of any applicable controls (NSCR catalyst, AFRC, etc.)

obtained from manufacturer data or actual test results.
17

Line 9: Enter the VOC control efficiency of any applicable controls (NSCR catalyst, AFRC, 

etc.) obtained from manufacturer data or actual test results.

Repeat the above input instructions for line 2 through 9 for each additional engine at the facility. 

4. EMISSION SOURCE DETAILS

A. Oil/Condensate Tanks

Vapors containing regulated pollutants are released from solution in hydrocarbon liquids as the 

liquids are transferred from higher to lower pressure, such as from a separator to an atmospheric 

storage tank. These vapors are called flashing losses.

Vapors escaping from hydrocarbon liquids while they are stored in atmospheric tanks are called 

standing/working/breathing (S/W/B) losses. Standing losses are essentially evaporation losses. 

Working losses are those caused by decreased tank vapor space occurring as the tank is filled. 

Breathing losses are those promoted by ambient changes such as increased air temperatures.

As used in this Guidance, the term, tank emissions include all S/W/B losses and flashing 

emissions together.

B. Calculating Tank Emissions

Tank emissions are calculated using the Oil & Gas Facility Emission Calculation Workbook. The 

workbook calculates the tank emissions by using either an actual direct measurement (scf/bbl)

taken by the owner/operator, a representative average or by using the default Bakken Pool 

emission factor of 97.91 scf/bbl described below. In addition to the scf/bbl value, the workbook 

uses the molecular weight, lower heating value of the fuel and the VOC and HAP weight 

fractions of the tank vapors to calculate the tank vapor emissions.

C. Bakken Pool Tank Vapor Emission Factor

In conjunction with the NDDoH, a VOC Emission Factor Committee was formed in 2010 to 

determine an emission factor that could be used for the Bakken Pool crude when calculating tank 

vapor emissions.

The VOC Emission Factor Committee consisted of representatives from various O&G

companies, as well as several environmental consultants. After reviewing the data from 89 direct 

measurements taken by several owner/operators within Mountrail County, the average emission 

factor of all measurements taken was 55.26 scf/bbl.

Many of the facilities could actually have emissions which are considerably higher than the 

average emission factor. Therefore, to better represent some of the higher emitting facilities and 

to avoid underestimating emissions, the 90th percentile (97.91 scf/bbl) will be utilized. If an 

owner/operator does not have direct measurement data to support a site specific emission factor, 

or an NDDoH pre-approved average scf/bbl emission factor established from direct 
18

measurements taken from a minimum of 6 different locations operating under similar parameters

(representative sample), the owner/operator must use the default value of 97.91 scf/bbl.

D. Tank Emissions Control Threshold

Tank emissions require control in accordance with Appendix D of this document. 

E. Tank Emissions Control Requirements

Emission control requirements for tank emissions are outlined in Appendix D of this document. 

Also see Appendix C for a list of acceptable control systems or devices.

F. Produced Water Tanks

At sites where tank emissions must be controlled by at least 90%, VOC and HAP emissions from 

all active produced water tanks shall be controlled by at least 90% within 60-days after the first 

date of production. See Appendix C for a list of acceptable control systems or devices.

G. Glycol Dehydrators

Glycol, usually tri-ethylene glycol (TEG), is used in dehydration units to absorb water from wet 

produced gas. “Lean” TEG contacts the wet gas and absorbs water. The TEG is then considered 

“rich.” As the rich TEG is passed through a reboiler and a flash separator (if installed) for 

regeneration, steam containing hydrocarbon vapors are released. These are then vented from the 

dehydration unit flash separator and/or reboiler still vent.

H. Calculating Glycol Dehydrator Emissions

The NDDoH recommends using GRI-GLYCalc V4.0 or higher to determine potential 

uncontrolled VOC and HAP emissions from the process vents of the dehydration unit associated 

with the projected (decline factor applied) first year average daily gas production rate. Other 

emission calculation programs may be used upon approval from the NDDoH. 

After running the program, print a copy of the report and include it with the Registration Packet 

submittal. The estimated VOC and HAP emission values also must be entered on Line 59 & Line 

60 on the Input Tab of the Emission Calculation Spreadsheet.

I. Glycol Dehydrator Control Threshold

Emissions that meet or exceed the following thresholds require the still vent vapors be routed to 

a control device: ≥ 5.0 TPY of any combination of HAPs, or ≥ 15.0 TPY any combination of 

VOCs.
19

J. Glycol Dehydrator Control Requirements

The following control systems or devices are accepted by the NDDoH for glycol dehydrator 

emissions:

1) An enclosed, smokeless combustion device or flare that is designed and operated to 

reduce the mass content of VOC and total HAP emissions in the vapors vented to the

device by at least 98% by weight.

2) Any other control device (e.g. condenser or ground pit flare) or configuration that can be 

demonstrated to reduce the mass content of total HAP and VOC in the process gases 

vented to the device or configuration by at least 90% by weight.

3) Glycol dehydrator emission controls may be removed after one year of operation 

provided emissions have declined to <15 TPY VOC and <5 TPY HAP. An updated GRIGLYCalc run with new calculations must be submitted to the NDDoH with a request for 

control removal. No controls may be removed prior to obtaining written approval from 

the NDDoH.

K. Glycol Dehydrator Federal Regulations

A Federal regulation (40 CFR 63, Subpart HH) may be applicable to glycol dehydrators located 

at Bakken Pool O&G production facilities. This regulation is beyond the scope of this document, 

but listed below is a brief summary of the regulation:

40 CFR 63, Subpart HH – National Emission Standards for Hazardous Air Pollutants from 

Oil and Gas Production Facilities

This federal regulation applies to all Bakken Pool O&G production facilities that are major and 

area sources of HAPs with the following exceptions:

1) A facility that exclusively processes, stores or transfers black oil.

2) A major source prior to the point of custody transfer with a facility-wide annual average 

natural gas throughput < 18.4 thousand cubic meters/day and a facility-wide annual 

hydrocarbon liquid throughput < 37,700 liters/day.

L. Calculating Treater Gas Flare Emissions

The treater flare emissions are calculated within the Oil & Gas Facility Emission Calculation 

Workbook using the following:

1) The projected first year average daily gas production rate. This is automatically 

calculated by multiplying the average daily rate entered on Line 1, by the decline factor 

entered on Line 3.

2) VOC & HAP weight fraction of gas

3) H2S mole percent of treater gas

4) Lower heating value of gas

5) Average molecular weight of gas
20

6) NOx & CO emissions are based on AP-42 emission factors for industrial flares.

M. Control Requirements for Treater Gas

Treater gas must be routed to a gas gathering pipeline as soon as practicable in accordance with 

the North Dakota Industrial Commission requirements. When a pipeline is not available, treater

gas is required to be routed to a control system or device. See Appendix C for a list of 

acceptable control systems or devices. That stated, the current opportunities to capture and 

transmit treater gas emissions necessitates the intermittent, or otherwise, use of combustion 

devices.

N. Natural Gas Fired Heaters & Burners

Some of the byproducts of natural gas combustion in process heaters, boilers, burners, etc. are 

regulated air pollutants. NOx, CO, VOC, HAP & SO2 emissions from process unit heaters are 

calculated within the Oil & Gas Facility Emission Calculation Workbook using the emission 

factors (EF) below from EPA AP-42, Tables 1.4-1, 1.4-2 and 1.4-3:

Table 1.4-1 Emission Factors from Natural Gas Combustion (Excerpt from AP-42, Tables 1.4-1, 

1.4-2 and 1.4-3)

Pollutant Natural Gas EF*

NOx 100 lb/MMscf

CO 84 lb/MMscf

VOC 5.5 lb/MMscf

HAPS 1.89 lb/MMscf

*Based on an average heating value of 1020 Btu/scf of natural gas. 

O. Truck Loading

When oil and condensate are loaded into tank trucks, the hydrocarbon vapors released from the 

tanker lines, as the truck is filling, contain regulated air pollutants. VOC emissions from loading 

oil or condensate into tank trucks are calculated within the Workbook by using the following 

formula with data from AP-42 tables.

LL = 12.46 × S × P × M/T

Where: LL = loading loss, pound per 1,000 gallons of liquid loaded (lb/1000 gal)

S = a saturation factor (See Table 5.2-1 below) 

P = true vapor pressure of liquid loaded (psia) 

M = molecular weight of tank vapors (lb/lb-mol) 

T = temperature of bulk liquid loaded (oR) (oR = oF + 460)

"S" values are obtained from Table 5.2-1. 

"M" and "P" values are obtained from Table 7.1-2.
21

Table 5.2-1 Saturation (S) Factors for Calculating Petroleum Liquid Loading Losses (Excerpt 

from AP-42, Table 5.2-1)

Cargo Carrier Mode of Operation* S Factor

Tank Truck and Rail Tank Cars Submerged loading of a clean cargo tank 0.50

Submerged loading: dedicated normal service 0.60

Submerged loading: dedicated vapor balance service 1.00

* Splash loading is not permitted in accordance with NDAC 33-15-07.

Table below may be used to provide the “P” and “M” values for the above equation:

Table 7.1-2 Properties of Selected Petroleum Liquids (Excerpt from AP-42, Table 7.1-2)

Petroleum 

Liquid

Crude Oil 

RVP 5

Vapor MW 

at 60 F 

MV(lb/lbmole)

50

Condensed 

Vapor 

Density at 

60F 

WVC(lb/gal)

4.5

Liquid 

Density at 

60F 

WL(lb/gal)

7.1

True Vapor Pressure, Pva (psi) at various temperatures in F

40 50 60 70 80 90 100

1.8 2.3 2.8 3.4 4.0 4.8 5.7

P. Truck Loading Control Requirements

Bakken Pool O&G production facilities are not required to route emissions displaced from truck 

loading activities to a control system or device due to safety concerns. However, the 

owner/operator shall follow any operating and/or construction requirements established in 

Chapters 33-15-07 and 33-15-20 of the North Dakota Air Pollution Control Rules.

Q. Reciprocating Internal Combustion Engines (RICE)

The emission calculation workbook requires g/bhp-hr values for VOC, NOx and CO in order to 

perform calculations for any particular engine. Those values may be obtained in three different 

manners and are listed below in order of preference.

Engine Emission Factor in Order of Preference

1) Actual Stack Test

2) Manufacturer’s Engine Data

3) AP-42 Values

While any of the three emission factors are acceptable by the NDDoH, actual test data from a 

particular engine, is usually the most accurate and preferred method. When test data is not 

readily available, manufacturer data for that particular engine model is the next best emission 
22

factor to be used. If neither test data, nor manufacturer data is available, AP-42 values should be 

used.

R. RICE Control Requirements

The NDDoH does not require any specific air pollution control equipment for RICE; however, 

the RICE must be in compliance with all State and Federal Rules and Regulations.

S. Federal Regulations for RICE

There are several Federal regulations that may be applicable to RICE located at Bakken Pool 

O&G production facilities. These regulations are beyond the scope of this document, but listed 

below is a brief summary of the Federal regulations that may be applicable. These regulations 

can be found at the following: http://ecfr.gpoaccess.gov.

40 CFR 60, Subpart IIII – Standards of Performance for Stationary Compression Ignition 

Internal Combustion Engines: Applies to any compression-ignition internal combustion engine 

where construction is commenced after July 11, 2005 and the engine is manufactured after April 

1, 2006.

40 CFR 60, Subpart JJJJ – Standards of Performance for Stationary Spark Ignition 

Internal Combustion Engines: Applies to any spark-ignition internal combustion engine where 

construction is commenced after June 12, 2006 and the engine is manufactured:

 After July 1, 2007 for engines > 500 hp

 After January 1, 2008 for lean-burn engines 500 < hp < 1350

 After July 1, 2008 for engines < 500 hp

 After January 1, 2009 for emergency engines

40 CFR 63, Subpart ZZZZ – National Emission Standards for Hazardous Air Pollutants 

for Stationary Reciprocating Internal Combustion Engines: Applies to any (new, existing, 

modified and reconstructed) RICE located at a major source or an area source of HAPs.

T. Pneumatic Pumps

If a pneumatic pump uses natural gas as the motive gas, the pump will release VOC and HAP 

emissions each time it strokes since all motive gas is vented by the pump. The Workbook 

calculates emissions from the pump based on the following:

1) Manufacturer’s information regarding gas usage (scf/hr)

2) The VOC & HAP weight fraction of the motive gas

3) Molecular weight of motive gas

4) Hours of operation
23

U. Pneumatic Pump Control Requirements

Bakken Pool O&G production facilities are required to control pneumatic pumps that use natural 

gas as the motive gas, if the PTE of VOCs from the pneumatic pump is >5 TPY per pump.

V. Pneumatic Controllers

If a pneumatic controller uses natural gas as the motive gas, the device will release VOC and 

HAP emissions each time it operates. The Workbook calculates emissions from the pump based 

on the following:

1) Manufacturer’s information regarding gas usage (scf/hr)

2) The VOC & HAP weight fraction of the motive gas

3) Molecular weight of motive gas

4) Hours of operation

W. Pneumatic Controller Control Requirements

Bakken Pool O&G production facilities are not required to install add-on controls for emissions 

from these types of devices.
24

5. EFFECTIVE DATE

This policy is effective on the date shown below. This policy does not supersede any applicable 

state or federal rule, regulation or law.

Any questions about this document should be directed to:

North Dakota Department of Health

Division of Air Quality

918 E Divide Avenue, 2nd Floor

Bismarck, ND 58501-1947

Phone: 701-328-5188

This document is available at: http://www.ndheath.gov/aq

Approved: Date: May 2, 2011

 Terry L. O’Clair, P.E.

 Director

 Division of Air Quality

 North Dakota Department of Health
25

APPENDIX A

Oil & Gas Production Facility Registration Form

Following is a copy of the NDDoH Oil/Gas Production Facility Registration Form (AP-114) 

which must be submitted as part of the registration packet within 90 days after the first date of 

production of a Bakken Pool O&G production facility. The form can be downloaded from the 

NDDoH website (http://www.ndhealth.gov/AQ/OilAndGasWells.htm) and is available in both 

Word and PDF formats. Also required is a copy of the gas analysis for the well and the first 

three pages of the Emission Calculation Workbook.
26
27
28

APPENDIX B

Oil & Gas Production Facility Emission Calculation Workbook Screenshots

The following pages represent screenshots of the Emission Calculation Workbook. The 

workbook is available for download from the NDDoH website in Excel format at: 

(http://www.ndhealth.gov/AQ/OilAndGasWells.htm

The workbook is intended to provide an easy way for owner/operators to calculate emissions for 

a Bakken Pool O&G production facility. With all owner/operators using the same emission 

workbook, it will help ensure that all emissions are calculated in a consistent manner from one 

owner/operator to another. It will also assist the NDDoH in tracking statewide emissions from 

Bakken Pool O&G production facilities.

Please note: the only Emission Calculation Workbook pages required in the Registration 

Packet are the Input Data Page, RICE Input Data Page and the Emission Summary Page

(applies to all submittals).
29

INPUT DATA PAGE
30

RICE INPUT DATA PAGE
31

EMISSION SUMMARY PAGE
32

OIL/CONDENSATE TANKS
33

TREATER FLARE
34

TREATER BURNER
35

TRUCK LOADING
36

RICE 
37

PNEUMATIC PUMPS
38

PNEUMATIC CONTROLLERS
39

APPENDIX C

NDDoH ACCEPTABLE CONTROL SYSTEMS OR DEVICES

The following VOC control systems or devices are accepted by the NDDoH:

1. A ground pit flare (including, but not limited to pit flares, shop built flares or other 

similar oilfield type flares) or other 90% or greater DRE device. If a ground pit flare is 

utilized, the NDDoH will allow a 90% DRE to be assumed. This is considered the 

minimum level of control for tank and treater gas emissions. 

2. A vapor recovery unit or oil stabilizer that is designed and operated to reduce the mass 

content of VOC and total HAP emissions in the vapors vented to the device by at least 

99% by weight. (Caution: a vapor recovery unit and oil stabilizer is used only to control 

tank emissions.)

3. An enclosed, smokeless combustion device or utility flare that is designed and operated 

to reduce the mass content of VOC and total HAP emissions in the vapors vented to the 

device by at least 98% by weight. A utility flare is any flare that is designed and operated 

in accordance with the requirements of NDAC 33-15-12-02, Subpart A 60.18 (40 CFR 

60.18). Requirements of 40 CFR 60.18 include, but are not limited to the following:

 Flare shall be designed and operated with no visible emissions except for periods 

not to exceed a total of 5 minutes during any 2 consecutive hours;

 Flare shall be operated with a flame present at all times;

 An owner/operator has the choice of adhering to either the heat content 

specifications in paragraph (c)(3)(ii) and the maximum tip velocity specifications 

in paragraph (c)(4) or adhering to the requirements in (c)(3)(i);

 Flares used to comply with this section shall be steam-assisted, air-assisted or 

nonassisted;

 Owners/operators of flares shall monitor the control devices to ensure that they 

are operated and maintained in conformance with their designs;

 Flares shall be operated at all times when emissions may be vented to them;

 Method 22 of Appendix A shall be used to determine the compliance of flares 

with the visible emission provisions of this subpart. The observation is 2 hours 

and shall be used according to Method 22;

 The presence of a flare pilot flame shall be monitored using a thermocouple or 

any other equivalent device to detect the presence of a flame. Daily checks by an 

operator to verify the existence of a visible flame or to verify proper operation of 

the igniter may be used in lieu of a physical device.

4. Control devices other than those listed above may be utilized upon approval from the 

NDDoH.

For safety and air pollution control purposes on all wells: each flare must be equipped and 

operated with an automatic ignitor or a continuous burning pilot, which must be maintained in 
40

good working order as outlined in NDAC 33-15-07-02. This is required even if the flare is used 

for emergency purposes only. Flares operating with automatic pilot systems are not required to 

operate with thermocouples.

Each combustion device must be installed with a thermocouple or any other equivalent device 

approved by the NDDoH designed to ensure the presence of a pilot on the device. Additionally, 

a continuous burning pilot is required if this department determines that an automatic ignition 

system is ineffective due to production characteristics. 

Emissions control equipment, systems or devices, all vent lines, connections, fitting, valves, 

relief valves, hatches or any other appurtenance employed to contain and collect vapors and 

transport them to the emission control system or device must be maintained and operated during 

any time a well is producing such that the emissions are controlled as outlined in Appendix D.

The owner/operator shall maintain and operate all air pollution control equipment in accordance 

with the manufacturer’s recommendations and in a manner consistent with good air pollution 

control practice for minimizing emissions. All reasonable precautions shall be taken by the 

owner/operator to prevent and/or minimize opacity from the operation of the flare or combustion 

device. A properly operating flare should be virtually free of opacity and a minimum of a visual 

check of a flare for opacity should be done whenever an operator is on site. Improperly 

operating equipment should be thoroughly inspected and if necessary, repaired as soon as 

possible. Compliance with opacity requirements will be based on applicable EPA Reference 

Methods.

The Department acknowledges that emission control equipment under an operating and 

maintenance plan will be off-line during routine maintenance and does not expect redundant 

equipment to be installed unless the uncontrolled emissions during that time cause the Bakken 

Pool O&G production facility emissions to exceed Title V or PSD thresholds. 
41

APPENDIX D

CONTROL REQUIREMENTS FOR TANK EMISSIONS

The following procedure must be followed to determine the level of control required for tank 

emissions from Bakken Pool O&G production facilities:

1. For production facilities where the first date of production occurred after June 1, 2011, 

tank emissions must be controlled by a ground pit flare (including, but not limited to pit 

flares, shop built flares or other similar oilfield type flares) or other control device that 

achieves at least a 90% DRE for VOCs upon startup of the facility.

2. For production facilities where the first date of production occurred after June 1, 2011, 

the owner/operator must calculate the VOC potential to emit (PTE) from tank emissions 

within 90 days after the first date of production and control VOC emissions as outlined in 

2.a and 2.b below. For production facilities where the first date of production occurred

on or before June 1, 2011, the owner/operator must calculate the VOC PTE from tank

emissions by September 1, 2011 and control VOC emissions as outlined in 2.a and 2.b

below.

a. If the PTE for VOC tank emissions is less than 20 tons/year, then a minimum of a 

ground pit flare (or other control device that achieves at least a 90% DRE for 

VOCs) is required to control VOC tank emissions.

b. If the PTE for VOC tank emissions is greater than or equal to 20 tons/year, then a 

control device that achieves at least a 98% DRE for VOCs must be installed and 

operated. 

3. It is possible that the PTE for VOC tank emissions will initially be calculated to equal or 

exceed 20 tons/year (which requires a control device with at least a 98% DRE for VOCs), 

but future calculations may result in a PTE for VOC tank emissions below 20 tons/year 

(which requires at least a ground pit flare or other control device that achieves at least a 

90% DRE for VOCs). In this case, the owner/operator may replace the 98% DRE control 

device with a 90% DRE control device after receiving written approval from NDDoH. A 

revised well registration packet shall be submitted to the NDDoH prior to the 

replacement of the control device.

4. At a minimum, tank emissions must be controlled by a ground pit flare (or other control 

device that achieves at least a 90% DRE for VOCs). In the event of a breakdown of any 

control equipment used to control tank emissions, the control equipment must be repaired 

in a timely manner.
42

APPENDIX E

The Basis for the 0.6 Factor and How it Relates to 80% Decline in Production for 

the First Year

The first year daily production rates are represented by the jagged line in BOX 1. The area 

under the line represents the total actual production volume for the first year. It is difficult to 

calculate the total volume under the jagged line so it is smoothed out in BOX 2 using statistical 

methods.

BOX 1 BOX 2

 

BOX 3 BOX 4

The smoothed curve is straightened out in BOX 3, and then leveled out in BOX 4. Now the 

production for the first year is represented by the area under the line in BOX 4 which is easily 

calculated. Production curves from a large sampling of wells indicate the average well declines 

Start Up 365 Days

 MMCFD

MMCFD

Actual production during the first year is 

represented by the area under the jagged line which 

ultimately turns out to be ~730 MMCF.

Start Up 365 Days

 MMCFD

The jagged line representing daily production is 

“smoothed” out using statistical methods.

Start Up 365 Days

 MMCFD

Start Up 365 Days

 MMCFD

2 MMCFD

Leveled” out, projected daily gas production rate 

vs. time

Total projected production for the first year is 

represented by the area under the straight line 

2 MMCFD x 365 days = 730 MMCF

The “smoothed” curve in BOX 2 is “straightened” 

out using mathematical methods.
43

by 80% during the first year. That 80% decline is represented by the level line in BOX 4 after 

the first 30-day average production rate is multiplied by 0.6.

Example: For the first month the well makes an average 3.333 MMCFD. With 80% decline 

during the first year, the well will make 0.667 MMCFD at the end of the first year (3.333 –

0.8(3.333) = 0.667). Then the average daily production rate over 365 days is (3.33 + 0.667)/2 = 

2.0 MMCFD which is the same as 3.333 x 0.6 = 2.0 MMCFD.