Guidance Regarding Tanks Associated with Multiple Wellpads

Generally, equipment associated with more than a single well pad does not report under the onshore petroleum and natural gas production industry segment of Subpart W. Note that onshore production storage tank calculations contemplate several distinct scenarios. First, emissions from atmospheric pressure fixed roof storage tanks receiving hydrocarbon produced liquids must calculate annual CH₄ and CO₂ emissions based on any applicable method listed under 40 CFR § 98.233(j).

Where separators upstream of the tanks have an annual average throughput of oil greater than equal to 10 barrels per day, please refer to Calculation Methodology 1 or 2 at 40 CFR 98.233(j)(1) and (2). If the well produces greater than or equal to 10 barrels per day, but produced oil does not pass through a wellhead separator before flowing to atmospheric storage tanks, please refer to Calculation Methodology 3 at 40 CFR 98.233(j)(3). For wells with annual average daily oil production greater than or equal to 10 barrels per day that flow to a separator not at the well pad, please refer to the methods at 40 CFR 98.233(j)(4). For wells with throughput less than 10 barrels per day, please refer to the equation W-15 at 40 CFR 98.233(j)(5).

Reporting Form Help

Please see Reporting Form Instructions on downloading the blank reporting form and uploading the completed reporting form.
You may also refer to Optional Calculation Spreadsheet Instructions to download the Subpart W calculation spreadsheet.

This page provides an overview of the Subpart W gas from produced oil sent to atmospheric tanks source category reporting requirements. The facility should report emissions collectively. Reporters are not restricted to using only one calculation methodology per sub-basin, and may use the requisite methods to report collective emissions, by sub-basin, for their facility.

The gas from produced oil sent to atmospheric tanks source category is applicable to Onshore Petroleum and Natural Gas Production.

Indicate if the facility has the source type via the radio buttons.

• If the source type is present you must report required elements.

If the facility has the source type, the Best Available Monitoring Methods and Missing Data table must be completed.

• For further information, see Best Available Monitoring Methods and Missing Data Reporting.

Worksheet Navigation

To navigate between tables use the navigational buttons provided at the top of the page and between tables or use the scroll bars.

Reporting Requirements

For wellhead gas-liquid separator with oil throughput greater than or equal to 10 barrels per day, using Calculation Method 1 and 2, the facility is required to report:

• Sub-basin ID - the pick list for this data element is populated based on the Sub-Basin Selection Tab.  Be sure a valid Sub-basin ID is used.
• Select calculation methodology used (Calculation Methodology 1 or Calculation Methodology 2) (98.236(c)(8)(i))
• Number of wellhead separators sending oil to atmospheric tanks (98.236(c)(8)(i)(A))
• Estimated average separator temperature (98.236(c)(8)(i)(A))
• Estimated average pressure (98.236(c)(8)(i)(B))
• Estimated average sales oil stabilized API gravity (98.236(c)(8)(i)(C))
• Count of hydrocarbon tanks at well pads (98.236(c)(8)(i)(D))
• Best estimate of count of stock tanks not at well pads receiving facility’s oil (98.236(c)(8)(i)(E))
• Count of tanks with vapor recovery system emissions control measures at well pads (98.236(c)(8)(i)(G))
• Count of tanks with flaring emissions control measures at well pads (98.236(c)(8)(i)(G))
• Best estimate of count of stock tanks assumed to have emissions control measures, not at well pads, receiving facility’s oil (98.236(c)(8)(i)(H))
• Minimum concentration of flash gas, CH₄ (98.236(c)(8)(i)(I) - this is a volumetric concentration, reported as a fraction
• Maximum concentration of flash gas, CH₄ (98.236(c)(8)(i)(I) - this is a volumetric concentration, reported as a fraction
• Minimum concentration of flash gas, CO₂ (98.236(c)(8)(i)(I) - this is a volumetric concentration, reported as a fraction
• Maximum concentration of flash gas, CO₂ (98.236(c)(8)(i)(I) - this is a volumetric concentration, reported as a fraction
• Annual CO₂ emissions that resulted from venting gas to the atmosphere (98.236(c)(8)(i)(J))
• Annual CH₄ emissions that resulted from venting gas to the atmosphere (98.236(c)(8)(i)(J))
• Annual CO₂ emissions that resulted from flaring gas (98.236(c)(8)(i)(L))
• Annual CH₄ emissions that resulted from flaring gas (98.236(c)(8)(i)(L))
• Annual N₂O emissions that resulted from flaring gas (98.236(c)(8)(i)(L)) 
• Are the only wells in the sub-basin wildcat or delineation wells subject to a 2-year delay in reporting? (98.236(c)(8)(i)(F)) 
• API Well Number(s) (98.236(c)(8)(i)(F)) 
• Total volume of oil from all wellhead separators sent to tank(s) (bbl per yr) (98.236(c)(8)(i)(F)) 
• Annual CO₂ gas quantities that were recovered (mt CO₂) (98.236(c)(8)(i)(K)) 
• Annual CH₄ gas quantities that were recovered (mt CO₂e) (98.236(c)(8)(i)(K)) 

For wellhead gas-liquid separator with oil throughput greater than or equal to 10 barrels per day, using Calculation Method 3 and 4, the facility is required to report:

• Sub-basin ID - the pick list for this data element is populated based on the Sub-Basin Selection Tab.  Be sure a valid Sub-basin ID is used.
• Select calculation methodology used (Calculation Methodology 3 or Calculation Methodology 4) (98.236(c)(8)(ii))
• Total number of wells sending oil directly to tanks. (98.236(c)(8)(ii)(B))
• Total number of wells sending oil to separators off the well pads. (98.236(c)(8)(ii)(C))
• Minimum sales oil API gravity for wells in 98.236(c)(8)(ii)(B) and 98.236(c)(8)(ii)(C) (98.236(c)(8)(ii)(D))
• Maximum sales oil API gravity for wells in 98.236(c)(8)(ii)(B) and 98.236(c)(8)(ii)(C) (98.236(c)(8)(ii)(D))
• Count of hydrocarbon tanks on well pads (98.236(c)(8)(ii)(E))
• Count of hydrocarbon tanks, on well pads, assumed to have vapor recovery system emissions control measures (98.236(c)(8)(ii)(F))
• Count of hydrocarbon tanks, on well pads, assumed to have flaring of tank vapors emissions control measures (98.236(c)(8)(ii)(F))
• Count of hydrocarbon tanks, off well pads, assumed to have vapor recovery system emissions control measures (98.236(c)(8)(ii)(F))
• Count of hydrocarbon tanks, off well pads, assumed to have flaring of tank vapors emissions control measures (98.236(c)(8)(ii)(F))
• Annual CO₂ emissions that resulted from venting gas to the atmosphere, at the sub-basin level for Calculation Method 3 or 4 (98.236(c)(8)(ii)(G))
• Annual CH₄ emissions that resulted from venting gas to the atmosphere, at the sub-basin level for Calculation Method 3 or 4 (98.236(c)(8)(ii)(G))
• Annual CO₂ emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 3 or 4 (98.236(c)(8)(ii)(I))
• Annual CH₄ emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 3 or 4 (98.236(c)(8)(ii)(I))
• Annual N₂0 emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 3 or 4 (98.236(c)(8)(ii)(I))
• Are the only wells in the sub-basin wildcat or delineation wells subject to a 2-year delay in reporting? (98.236(c)(8)(ii)(A))
• API Well Number(s) (98.236(c)(8)(ii)(A))
• Total volume of sales oil from all wells (bbl per yr) (98.236(c)(8)(ii)(A))
• Annual CO2 gas quantities that were recovered (mt CO2) (98.236(c)(8)(ii)(H))
• Annual CH4 gas quantities that were recovered (mt CO2e) (98.236(c)(8)(ii)(H))

For wellhead gas-liquid separator with oil throughput less than 10 barrels per day, using Calculation Method 5, the facility is required to report:

• Sub-basin ID - the pick list for this data element is populated based on the Sub-Basin Selection Tab.  Be sure a valid Sub-basin ID is used.
• Total volume of oil production (98.236(c)(8)(iii)(C))
• Best estimate of fraction of production sent to tanks with assumed vapor recovery system control measures (98.236(c)(8)(iii)(D))
• Best estimate of fraction of production sent to tanks with assumed flaring of tank vapors control measures (98.236(c)(8)(iii)(D))
• Count of hydrocarbon tanks on well pads (98.236(c)(8)(iii)(E))
• Annual CO₂ emissions that resulted from venting gas to the atmosphere, at the sub-basin level for Calculation Method 5 (98.236(c)(8)(iii)(F))
• Annual CH₄ emissions that resulted from venting gas to the atmosphere, at the sub-basin level for Calculation Method 5 (98.236(c)(8)(iii)(F))
• Annual CO₂ emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 5 (98.236(c)(8)(iii)(H))
• Annual CH₄ emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 5 (98.236(c)(8)(iii)(H))
• Annual N₂O emissions that resulted from flaring gas, at the sub-basin level for Calculation Method 5 (98.236(c)(8)(iii)(H))
• Number of wellhead separators (98.236(c)(8)(iii)(A))
• Number of wells without wellhead separators (98.236(c)(8)(iii)(B))
• Annual CO₂ gas quantities that were recovered (mt CO₂) (98.236(c)(8)(iii)(G))
• Annual CH₄ gas quantities that were recovered (mt CO₂e) (98.236(c)(8)(iii)(G))

If wellhead separator dump valve is functioning improperly during the calendar year, the facility is required to report:

• Sub-basin ID - the pick list for this data element is populated based on the Sub-Basin Selection Tab.  Be sure a valid Sub-basin ID is used.
• Count of wellhead separators that dump valve is applied (98.236(c)(8)(iv)(A))
• CO₂ emissions from improperly functioning dump valves (98.236(c)(8)(iv)(B))
• CH₄ emissions from improperly functioning dump valves (98.236(c)(8)(iv)(B))

Total Emissions

The total emissions roll-up at the top of the sheet reflects the sum of the CO₂ equivalents of each gas emission reported for the source type.  These summations are reflected and aggregated on the Introduction tab.