Reducing Emissions: Best Practice Guide Venting November 2019 Disclaimer This document has been developed by the Methane Guiding Principles partnership. The Guide provides a summary of current known mitigations, costs, and available technologies as at the date of publication, but these may change or improve over time. The information included is accurate to the best of the authors’ knowledge, but does not necessarily reflect the views or positions of all Signatories to or Supporting Organisations of the Methane Guiding Principles partnership, and readers will need to make their own evaluation of the information provided. No warranty is given to readers concerning the completeness or accuracy of the information included in this Guide by SLR International Corporation and its contractors, the Methane Guiding Principles partnership or its Signatories or Supporting Organisations.

This Guide describes actions that an organisation can take to help manage . Any actions or recommendations are not mandatory; they are simply one effective way to help manage methane emissions. Other approaches might be as effective, or more effective in a particular situation. What readers choose to do will often depend on the circumstances, the specific risks under management and the applicable legal regime. Contents

Summary...... 2

Introduction...... 3

Quantifying emissions...... 6

Mitigation strategies...... 7

Checklist...... 14

References...... 15

1 Summary

Venting is releasing gas into the atmosphere. Best practice for reducing methane emissions This guide intends to help you identify the major from venting sources of venting and reduce methane emissions from them. Keep an inventory of emissions from venting The general strategies for reducing emissions are as follows; Avoid or reduce venting from the following • liquid storage tanks

• Compressor seals and starter motors

• Glycol dehydrators

• Removing liquids from gas wells

• Well-completion operations

• casinghead venting

If methane needs to be released, use vapor recovery or flaring rather than venting if possible

Monitor vents and evaluate for further improvements and controls

2 Introduction

Venting simply means releasing gas into the compressors and dehydrators. It also deals with atmosphere. Methane can be vented intentionally gas from the following activities: from processes or activities that are designed • well completions; and to vent gas, or unintentionally when equipment malfunctions or operations are not normal. • removing liquids from gas wells.

This guide focuses on a few common venting Venting occurs across all parts of the gas supply sources and strategies for reducing emissions. chain and from a variety of activities. This guide It does not deal with all venting sources. In this focuses on equipment and activities that are known guide, venting refers to gas vented from key to be major sources of emissions. Table 1 below equipment, such as wellheads, storage tanks, sets out which types of equipment are major sources of emissions. Table 2 sets out the activities that are major sources of emissions.

Table 1: Equipment known to be major sources of emissions from venting

Equipment Where When emissions occur Condition Area of emissions when operations come from emissions occur

Storage tanks Flash gas at Tanks can have emissions Normal Most ‘produced for produced tanks with related to the flashing operation liquids’ storage liquids, such no vapor- of light gases that result tanks exist in as condensate, recovery units from receiving pressurized production, but crude oil, or (uncontrolled liquids from other vessels. some also exist in water tanks) Most often tanks are near processing and in atmospheric pressure, but transmission and upstream vessels can be at a storage. much higher pressure.

Tank loading Gas is released when a tank Routine and unloading, is opened at the hatch or activity and tank when there is loading into gauging the truck or rail tanker.

Vapor Gas is released from the tank Faulty or blowthrough as a result of a gas stream inadequate to a tank unintentionally sent from an upstream upstream vessel. equipment, especially at separators

3 Introduction

Table 1: Equipment known to be major sources of emissions from venting (continued)

Equipment Where When emissions occur Condition Area of emissions when operations come from emissions occur

Compressors Packing Normal losses occur at Normal Compressors around rods on the mechanical seal of the operation are used in reciprocating packing around the rod. production, compressors gathering and boosting, Wet seals on Normal losses occur at Normal processing, and centrifugal the mechanical seal of the operation transmission and compressors rings around the rotating storage, and also compressor shaft. the export of liquid . Starter motors Periodic emissions are Normal (gas powered) released from the starter operation motor when an idle compressor is started.

Glycol Regenerator Water absorbed by the Normal Dehydrators dehydrators vent stack not circulating glycol exits operation are used in routed to flare through the regenerator production, reboiler’s vent stack to the gathering and atmosphere. Absorbed boosting, and methane is also released. storage.

If a gas assist lean glycol pump is used, this can add to emissions.

Wellheads Casinghead Some oil wells that do not Normal Production of oil vent gas produce gas to sales will operation vent the annual space in the casing to the atmosphere.

4 Introduction

Table 2: Activities known to be major sources of emissions from venting

Activity What causes When emissions occur Condition Area of emissions when operations emissions occur

Well Clearing After drilling, a new well Normal process Production only completions unwanted is brought into production liquids, solids by clearing the well of drill and gas from cuttings, sand and fracturing the well after fluid. This process, and the drilling and process of testing the well fracturing afterwards, can result in venting or flaring of gas.

Removing Removing Gas is often released to the Well is offline Production only liquids from accumulated atmosphere when a well is and gas gas wells (also liquids from allowed to flow directly to a flows to the called “liquids low-pressure lower-pressure source, such atmosphere. unloading”) gas wells as an atmospheric tank, to This only clear the well. occurs for certain types of liquids unloading procedures.

The emission sources this guide deals with make up about 16% of the total methane emissions from the US and natural gas systems.1,2

Some sources of venting are covered in other best-practice guides, such as venting during equipment maintenance blowdowns, which is covered in the guide on operational repairs, venting from pneumatic devices, which is covered in a separate guide on pneumatics, and venting from unlit flares, which is covered in the flaring guide.

5 Quantifying emissions

Quantification methods for methane emissions deliver a rate, such as mass per time (e.g. kilograms per hour) or volume per time (e.g. standard cubic meters per hour), and can be produced by engineering estimations, by direct measurement of the methane sources, or by use of models. Vented emissions are quantified based on the following methods, listed in order of increasing accuracy and reliability.

• Default emission factors – emissions are quantified by multiplying the number of pieces of equipment (or venting activities) by the average emission rate per piece of equipment or per process.

• Engineering calculations – equations to calculate emissions may use a variety of information gathered locally to quantify the rate from certain processes or activities. In some cases, this may involve running a computer program (for example, tank flash emissions and glycol dehydrator regenerator emissions). In those cases, a simulation program may be used to predict emissions based on first principles and equations of state.

• Direct measurement of emissions – this may be done using information from routine monitoring or, in some cases, continuous monitoring.

There are several accepted and recommended methods of direct measurement in ‘Best Practice Guidance for Methane Management in the Oil and Gas Sector’ (United Nations Economic Commission for Europe).3 Those methods include using:

• a calibrated vent bag;

• a high-volume sampler;

• flow meters; or

• anemometers.

Direct measurement requires a repeatable approach with written procedures, and different measurement approaches carry their own unique uncertainties. In some cases, getting an accurate direct measurement can be difficult, and engineering approaches may be preferred.

6 Mitigation strategies

Strategies for reducing emissions from venting involve the following.

• Reducing or eliminating the source of the emissions through effective operations and design.

• Directing the emissions to a control device to prevent direct emission of methane to the atmosphere.

• Where venting cannot be avoided, vents should be tracked and/or monitored and evaluated for further improvements or controls.

Methane is a valuable product that can be sold, – Number 8: ‘Well Venting/Flaring During so equipment and activities have been designed Well Completion for Hydraulically Fractured to minimize venting. The need for some venting Gas’, 2017 can be reduced by making changes to operations, – Number 9: ‘Casinghead Gas Venting’, 2017 recovering gas to be reused, or flaring (burning) the gas. Some venting will be necessary for safety, • Natural Gas Star Program’s ‘Recommended technical or cost-efficiency reasons. When venting Technologies to Reduce Methane Emissions’, a is necessary, it should be monitored and assessed program by the United States Environmental 11 to make sure it is minimized whenever possible. Protection Agency (www.epa.gov/natural- gas-star-program/recommended-technologies- The emission sources covered in this guide have reduce-methane-emissions) been studied for decades. There are several guides • United Nations Economic Commission for on reducing these methane emissions. The guides Europe’s ‘Best Practice Guidance for Methane and programs specific to natural gas systems Management in the Oil and Gas Sector’, August include the following. 20193

• Climate and Clean Air Coalition’s (CCAC) Oil and • Norwegian Environment Agency’s ‘Cold venting Gas Methane Partnership technical guidance and fugitive emissions from Norwegian offshore 4,5,6,7,8,9,10 documents: oil and gas activities’, a summary report prepared 12 – Number 3: ‘Centrifugal Compressors with Wet by Add Energy, April 2016 (Oil) Seals’, 2017 This best-practice guide does not provide – Number 4: ‘Reciprocating Compressors Rod information on all reduction methods available as Seal/Packing Vents’, 2017 not all methods apply to the vented emissions this – Number 5: ‘Glycol Dehydrators’, 2017 guide covers.

– Number 6: ‘Unstabilized Hydrocarbon Liquid Recommended mitigation strategies for specific Storage Tanks’, 2017 vented sources are summarized in table 3. – Number 7: ‘Well Venting For Liquids Unloading’, 2017

7 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting

Source of Mitigation Description Effectiveness Source of emissions strategy information

Storage tanks Add vapor- The main option is installing 95% reduction CCAC7 technical – flash gas recovery units a VRU for directing the in emissions if guidance (VRUs) emission to be reused, sold the VRU has a document 6 or flared. high reliability. EPA Gas Star11

NEA12

Eliminate tanks Add lease automatic custody 100% EPA Gas Star11 at production transfer (LACT) systems to reduction sites transfer the oil or gas to a pipeline.

Storage tanks Add automatic Automatic gauging may 100% Emerson guide13 – opening and gauging eliminate the need to open reduction loading liquids systems tank hatches, and so can from tanks to reduce tank emissions. trucks Introduce a Vapor return lines can Variable EPA Gas Star11 system to be installed to collect or balance or control gases displaced in exchange the truck when transferring gases between liquids from tanks to trucks. the tanks and The gases may either be tanker vehicles returned to the tanks (vapor balance) or sent direct to a control device.

Storage Add pressure Tank pressure monitors Variable US EPA tanks – vapor monitors to in a SCADA (supervisory Settlements14, 15, 16 blowthrough tanks control and data acquisition) from upstream system can alert operators vessels of overpressure conditions that may result in direct emissions to the atmosphere.

8 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting (continued)

Source of Mitigation Description Effectiveness Source of emissions strategy information

Storage Routine Routine monitoring of Variable CCAC7 technical tanks – vapor monitoring dump valves to make sure guidance blowthrough they are working properly, document 6 from upstream and routine monitoring of vessels storage-tank hatches and NEA12 (continued) safety valves, such as with an OGI camera, will allow earlier detection of vapor blowthrough.

Compressors Conduct Add regular monitoring to a Variable CCAC5 technical – packing regular periodic leak detection and guidance around rods on monitoring repair (LDAR) program. document 4 reciprocating The information from the compressors program can be used to either assess opportunities for reducing venting or monitor improvement after mitigation efforts.

Regularly The timing of replacements A 50 to 65% CCAC5 technical replace packing can be scheduled or based reduction in guidance around rods on inspections. Scheduled emissions is document 4 replacements should be expected carried out at least every three years, or as soon as excessive venting is identified.

This strategy is most relevant to compressors that are spared (can be stopped without affecting production).

Direct Emissions could be directed 95% reduction CCAC5 technical emissions to a to a flare or another device guidance control device such as catalytic destruction document 4 control.

9 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting (continued)

Source of Mitigation Description Effectiveness Source of emissions strategy information

Compressors Regularly Add to periodic LDAR Variable CCAC4 technical – wet seals monitor program. guidance on centrifugal sources document 3 The information from compressors of vented the LDAR program emissions NEA12 can be used to either assess opportunities for reducing venting or monitor improvement after mitigation efforts.

For information on developing an LDAR program, please see the best-practice guidance relating to equipment leaks.

Direct Emissions could be directed 95% reduction CCAC4 technical emissions to a to a flare or another device guidance control device such as catalytic destruction document 3 control. NEA12

Convert wet Dry seals generally use Variable CCAC4 technical seals to dry less power and are more guidance seals reliable. However, replacing document 3 seals requires a lengthy and EPA Gas Star11 often expensive compressor shutdown.

Operators should buy new compressors that have dry seals (about 90% of products on the market have dry seals).

10 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting (continued)

Source of Mitigation Description Effectiveness Source of emissions strategy information

Compressors Convert gas Gas starter motors use the 100% EPA Gas Star11 – gas starter starter motors energy in the pressurized reduction NEA12 motors to electric gas to spin a turbine to start starter motors the compressor. Converting to electric power eliminates the need for gas power.

(Note: An electricity supply is sometimes unavailable, or less reliable than gas pressure at the site.)

Switch starters A compressed-air system 100% EPA Gas Star11 to compressed at a facility often cannot reduction NEA12 air power gas starter motors and is less reliable than gas (EPA Gas Star) pressure at the site.

Recover or There must be large short- 95% reduction EPA Gas Star11 flare the gas term capacity in the VRU or from the starter flare. motor

Glycol Replace a Replacing the pump 100% CCAC6 technical dehydrators gas-assist lean eliminates the need for reduction in guidance – regenerator glycol pump gas that is discharged into pump-added document 5 vent stack with an electric the glycol stream and then emissions lean glycol vented. pump

Install a flash (Note: Some newer control 90% reduction CCAC6 technical tank separator, systems automatically shut guidance recover gas, down the dehydrator if the document 5 and optimize VRU system recovering the NEA12 flash tank gas goes down.) glycol- circulation rates

Replace with Change technology for 100% CCAC6 technical a ‘near-zero dehydration (for example, reduction guidance emissions’ desiccant) dehydrators. document 5 dehydrator system

11 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting (continued)

Source of Mitigation Description Effectiveness Source of emissions strategy information

Well Recover or flare Gas can be recovered by 95% reduction CCAC10 technical casinghead the gas from a new vapor recovery unit in emissions if guidance vent the oil well (VRU) or by routing the gas the VRU has a document 9 casinghead to an existing vapor recovery high reliability. vent unit on tanks if one already For flare, 95%. exists at the site. If recovery is not possible, flare the gas.

Well Introduce The objective of the Roughly 90% CCAC9 technical completions a reduced- technology is to capture the reduction guidance emission flowback gas so it can be document 8 (green) sold, or flare it as soon as completion possible, rather than venting. system This step requires special flowback equipment. Install portable equipment during the final stage of a well completion that is designed for a high flow rate of water, sand and gas, and capture gas so it can be sold.

Removing Manual liquids Remove liquids by manually Unknown, CCAC8 technical liquids from unloading: venting the well through an variable guidance gas wells (also minimize time atmospheric tank, but only document 7 called “liquids under direct supervision unloading”) (eliminate unattended unloadings).

Alter the well Operators have a number 100% CCAC8 technical and downhole of options for removing reduction guidance operation so liquids from the well that document 7 that periodic would eliminate the need for venting is not venting. Examples include needed adding foaming agents, soap strings or surfactants; installing velocity tubing; installing gas-lift compressors; or adding well pumps.

12 Mitigation strategies

Table 3: Mitigation strategies for emissions from venting (continued)

Source of Mitigation Description Effectiveness Source of emissions strategy information

Use automated In some cases, an operator Unknown, CCAC8 technical liquids can install an automated variable guidance unloading plunger lift system that document 7 periodically drops a plunger to remove liquids. This method can be designed to eliminate venting.

13 Checklist

The following checklist allows you to assess your progress in reducing methane emissions from venting. You can introduce the strategies across all sites and equipment or start with only a selection.

Activity Completed Percentage of equipment or sites

Keep an inventory of emissions from venting

Avoid or reduce venting from the following

• Oil well casinghead venting

• Hydrocarbon liquid storage tanks

• Compressor seals and starter motors

• Glycol dehydrators

• Removing liquids from gas wells

• Well-completion operations

If methane needs to be released, use vapor recovery or flaring rather than venting

Monitor vents and evaluate for further improvements and controls

14 References

1 United States Environmental Protection Agency 9 Climate and Clean Air Coalition’s Oil and Gas (US EPA) ‘2017 Greenhouse Gas Reporting Methane Partnership Technical guidance Program Industrial Profile: Petroleum and document 8: ‘Well Venting/Flaring During Well Natural Gas Systems’ (October 2018) Completion for Hydraulically Fractured Gas Wells’ (2017) 2 US EPA ‘Inventory of Greenhouse Gas Emission and Sinks, 1990-2017’ (April 2019) 10 Climate and Clean Air Coalition’s Oil and Gas Methane Partnership Technical guidance 3 United Nations Economic Commission for document 9: ‘Casinghead Gas Venting’ (2017) Europe (UNECE) ‘Best Practice Guidance for Methane Management in the Oil and Gas 11 Natural Gas Star Program ‘Recommended Sector: Monitoring, Reporting and Verification Technologies to Reduce Methane Emissions’, a (MRV) and Mitigation’ (August 2019) program by the United States Environmental Protection Agency Available from www.epa. 4 Climate and Clean Air Coalition’s Oil and Gas gov/natural-gas-star-program/recommended- Methane Partnership Technical guidance technologies-reduce-methane-emissions document 3: ‘Centrifugal Compressors with Wet Oil Seals’ (2017) 12 ‘Cold venting and fugitive emissions from Norwegian offshore oil and gas activities’, a 5 Climate and Clean Air Coalition’s Oil and Gas summary report prepared for the Norwegian Methane Partnership Technical guidance Environment Agency (NEA) by Add Energy document 4: ‘Reciprocating Compressors Rod (April 2016) Seal/Packing Vents’ (2017) 13 Emerson ‘The Engineer’s Guide to Tank 6 Climate and Clean Air Coalition’s Oil and Gas Gauging’ (2017) Methane Partnership Technical guidance document 5: ‘Glycol Dehydrators’ (2017) 14 US Environmental Protection Agency ‘HighPoint Operating Corporation Clean Air 7 Climate and Clean Air Coalition’s Oil and Gas Act Settlement’ (April 2019) Available at www. Methane Partnership Technical guidance epa.gov/enforcement/highpoint-operating- document 6: ‘Unstabilized Hydrocarbon Liquid corporation-clean-air-act-settlement Storage Tanks’ (2017) 15 US Environmental Protection Agency ‘Noble 8 Climate and Clean Air Coalition’s Oil and Gas Energy, Inc. Settlement’ (April 2015) Available Methane Partnership Technical guidance at www.epa.gov/enforcement/noble-energy- document 7: ‘Well Venting for Liquids inc-settlement Unloading’ (2017) 16 16. US Environmental Protection Agency ‘MarkWest Clean Air Act Settlement Information Sheet’ (May 2018) Available at www.epa.gov/enforcement/markwest-clean- air-act-settlement-information-sheet

15 References

17. American Petroleum Institute ‘Consistent Methodology for Estimating from Liquefied Natural Gas (LNG) Operations’, version 1 (May 2015)

18. Gas Research Institute and the US Environmental Protection Agency ‘Methane Emissions from the Natural Gas Industry’, Volume 14: Glycol Dehydrators (1996)

19. American Petroleum Institute ‘Compendium of Greenhouse Gas Emissions Methodologies for the Oil and Natural Gas Industry’ (2009)

20. Michael McMahon ‘Capturing the Tank Vapor Opportunity: Removing Oxygen from the Production Stream Reduces Emissions and Generates Incremental Economics’, presentation at the Laurance Reid Gas Conditioning Conference, February 25-28, 2019 Available at www.ecovaporrs.com/ wp-content/uploads/EcoVapor-Laurance- Reid-Paper-Capturing-the-Tank-Vapor- Opportunity.pdf

21. Kent A Pennybaker and River City Engineering Inc Society of Petroleum Engineers ‘Optimizing Field Designs’ (March 1998)

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