ƒAll over the media there is news about climate change and greenhouse gases (GHGs).  Many in the oil and gas industry do not work directly with GHG issues but most realize that this issue will greatly affect their companies.  This is a brief summary of GHGs and the oil and gas industry.


What are the GHGs of concern?

The EPA greenhouse gases (GHG) requiring reporting by industry include the following:


Greenhouse Gas Chemical formula Primary Emission Sources Requires Annual Reporting for O&G?
Carbon dioxide CO2 Combustion of fossil fuels Yes
Methane CH Venting of Natural Gas Yes
Nitrous oxide N2O Combustion of fossil fuels Yes
Fluorinated gases Various Not emitted by O&G processes No

The GHG pollutants of greatest concern for O&G are CH4 and CO2.  N2O emissions, primarily from burning fuels, is not very large for oil and gas operations based on current emission calculation factors.


EPA Mandatory GHG Reporting Regulations – 40 CFR 98

The EPA’s GHG reporting rules are contained in 40 CFR 98 – Mandatory Greenhouse Gas Reporting.  The rule requires reporting of greenhouse gas (GHG) emissions from all sectors of economy.  At this time there is no requirement to require control GHGs.  The GHG data reported is being analyzed by the EPA and will be used for future regulation of facilities.

The rule requires a facility that has actual emissions of 25,000 metric tons or more of CO2e per year to submit an annual report of GHG in electronic format to the EPA.


Applicability of 40 CFR 98

Two subparts affecting the oil and gas industry include:

  • 40 CFR 98 Subpart C – separate requirement for stationary combustion sources (e.g., engines, heaters, etc.) affecting offshore, gas gathering, gas processing and transmission, gas storage, and LNG facilities. First report was for year 2010.
  • 40 CFR 98 Subpart W – Petroleum and Natural Gas Industry – primarily flare/vent/fugitive sources. For oil and gas production facilities, the rule includes stationary and portable combustion sources (e.g., engines, heaters, etc.).  First report was for year 2011.

GHG reports are for actual emissions, unlike air permits which for potential to emit (PTE) emissions.

Subpart W has different reporting requirements based on the source categories listed below:

  • Onshore petroleum & nat. gas production
  • Offshore petroleum & nat. gas production
  • Onshore nat. gas processing plants
  • Onshore nat. gas transmission
  • Underground nat. gas storage
  • Liquefied natural gas (LNG) storage
  • LNG gas import & export equipment
  • Natural gas distribution

This write up focuses on onshore petroleum and natural gas production GHG reporting to EPA.


Basins and Onshore O&G GHG Reporting

For the onshore petroleum and natural gas production category, operators must calculate actual GHG emissions and aggregate all GHG emissions from affected emission sources located in a “Basin.”  The aggregated emissions from each “Basin” is considered a facility and the GHG reporting unit.  The “Basin” map used is a map by the Am. Assoc. of Pet. Geol. (AAPG) Geologic Provinces Code Map: AAPG Bulletin, Vol. 75, No. 10 (October 1991).  To review the map go to:  AAPG Basin Map Link.

Note that this is a departure from state air permits that are typically required for aggregated emissions from a cleared well pad area.


Affected Equipment for Oil and Gas

Equipment required to be track and reported include:

  • Natural gas pneumatic devices
  • Natural gas driven pneumatic pumps
  • Well venting for liquids unloading
  • Gas well venting – well completions
  • Gas well venting – well workovers
  • Flare stack emissions
  • Storage tanks
  • compressor rod packing
  • Well testing venting and flaring
  • gas venting and flaring
  • Dehydrator vents
  • EOR injection pump blowdown
  • Acid gas removal vents
  • EOR hydrocarbon liquids dissolved CO2
  • Centrifugal compressor venting
  • Fugitive emissions – equipment leaks
  • Engines (drilling rigs and stationary engines), heaters, reboilers, etc. using methods in 40 CFR 98 Subpart C


Global Warming Potentials (GWP)

Each GHG is assigned a global warming potential (GWP) to account for how much heat a greenhouse gas traps in the atmosphere.  The GWPs are found in 40 CFR 98 Subpart A, Table A-1.  The GWPs are used to convert the mass amount of the specific GHG to Carbon Dioxide Equivalent (CO2e).  The GWP factors for CH4 and N2O were updated for the 2013 reporting year.


GHG Name Chemical formula Global warming potential factor
Carbon dioxide CO2 1
Methane CH4 25
Nitrous oxide N2O 298

For example, if a facility emits 1000 metric tons of CH4, then its CO2e would be calculated as:  (1000 metric tons CH4)(25 tons CO2e/ton CH4) = 25,000 metric tons CO2e.


How much is 25,000 metric tons CO2e?   

25,000 metric tons CO2e is equivalent to approximately:

  • Combustion of 1.29 million standard cubic feet per day (MMSCFD) of natural gas for an entire year (varies with BTU value of the natural gas burned)
  • Venting 143 thousand standard cubic feet per day (MSCFD) of methane


Applicability to Offshore Operations and GOADS

Offshore petroleum and natural gas production facilities are required to use the data or methods in the BOEM Gulfwide Offshore Activities Data System (GOADS) inventory to report their Subpart W flaring/venting GHG emissions.  Platform combustion sources (engines, heater, etc.) must use 40 CFR 98 Subpart C to calculate GHG emissions.  The Subpart C and W annual emissions for affected facilities are reported separately using the e-GGRT system.

For BOEM regulated production platforms in the Central and Western Outer Continental Shelf (OCS) of the Gulf of Mexico must use most recent published final GOADS reporting data.  Offshore oil and gas production facilities not under BOEM jurisdiction (territorial seas, coastal areas), must use the calculation methods used by GOADS.  GOADS is typically on a 3-year cycle, with 2017 being a reporting year for GOM OCS facilities.


Emission Calculations/Measurement

The calculation methods in the rule are very prescriptive and use language that specifies the required activity data, equations, simulation models and emission factors to be used.

There is some flexibility in regards to the use of direct measurement of vents for storage tanks and venting from well from unloading operations and other associated venting and flaring sources.  Where allowed by EPA, operators are using direct measurement of vent gas for GHG reporting in lieu of using EPA emission factors.  Direct measurement can more accurate data and possibly lower emissions than the EPA GHG emission factors.


Data Management

For GHG reporting there are two types of data collected for emission sources:

  • Descriptive data that includes make, model, capacity, size, horsepower, MMBTU/hr rating, emission controls design capacity, etc.
  • Activity data includes fuel used, throughput, volumes of natural gas vented or flared, hours operating, hours venting/flaring, etc.


The activity data is tracked during the calendar year and used with the descriptive data and GHG prescribed calculation methods to yield the annual total CO2e emissions for each emission source and facility required to report.

Many operators are using databases and environmental management systems to collect, manage, and archive data used for GHG reporting.  Automation of data collection is rapidly occurring.  This will lower compliance costs and reduce transcription errors that can occur when transferring data from one system to an Excel spreadsheet based system.


Recordkeeping for GHG Reports

Extensive recordkeeping of all records used to generate GHG reports are required to be kept for at least 3 years from the date of submission of the annual GHG report for the reporting year in which the record was generated.


Annual Reporting Under 40 CFR 98

March 31 of each year is the normal due date for the required annual GHG report.  The report must be submitted in the EPA required electronic format using the EPA’s e-GGRT system.  The report is for the previous calendar year.  New e-GGRT users must complete a one-time registration process. After establishing a user account the user can register and report for their facilities.

If a facility’s (Basin aggregate for oil and gas production) GHG emissions are reduced to below 25,000 metric tons per year for 5 consecutive years, then the facility can submit a notification to the EPA to discontinue reporting.  If GHG emissions are below 15,000 metric tons per year for 3 consecutive years, then the facility can also submit a notification to EPA to discontinue reporting.  If the facility ceases operations or is transferred to another operator, then a notification can be sent to stop reporting for the year following cessation of operations or transfer of facility.


Certification by Designated Representative for GHG Reports

All reports require certification by the company’s designated representative to submit the electronic report as defined in 40 CFR 98 Subpart A – General Provisions.  This is done via e-GGRT system.



GHG Emission Controls

The reporting rule does not require oil and gas operators to control GHG emissions.  The EPA is analyzing the data from previous reports.  Many expect the regulation of GHG emissions, including emission controls, in the future.

Typical methods to reduce emissions would be to reduce venting, flaring and fuel usage.

Some operators are electing to voluntarily reduce their vented CH4 emissions by measuring the actual flowrate of vent gas along with a chemical analysis of the vent gas.  Actual flowrates and chemical analyses result in lower actual CH4 emissions.  Also, using the measurement data, the operator can better size their Vapor Recovery Systems.

Remember:  Reducing 1 ton of CH4 is the same as reducing 25 tons of CO2e.

Capture associated natural gas to reduce the reporting burden.


Stay in Compliance

Cimarron can assist your company with NSPS OOOO and OOOOa compliance. Our thorough understanding of oil and gas processes and expertise with storage tank emission controls (VRUs, VRTs, VCUs) and leak monitoring makes us a leader in providing certainty to your compliance needs.

Our IQR (Identify, Quantify and Rectify) services include fugitive leak monitoring (LDAR) that meets NSPS OOOOa requirements. Our IQR services can also assist with emission controls selection for your facility.

Check out Cimarron Energy’s Tankless Facilities at: as a way to produce without storage tanks.

Posted Under: Blog

Leave a Reply

Your email address will not be published. Required fields are marked *