# Presentation: 545614

## Vapor Recovery and Gathering Pipeline Pigging 

- Lessons Learned from Natural Gas STAR
- Chevron Corporation,
- New Mexico Oil and Gas Association,
- Texas Oil and Gas Association
- Producers and Processors Technology Transfer Workshop
- Midland, Texas
- July 23, 2008
- epa.gov/gasstar

## Reduction Opportunities: Agenda

- Industry Emissions
- Selected Methane Saving Opportunities
- Vapor Recovery Units
- Pipeline Pigging
- Discussion

## Industry Emissions: Production, Gathering, and Boosting

- Source: EPA. *Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990 – 2006. *April, 2008. Available on the web at: epa.gov/climatechange/emissions/usinventoryreport.html
- Note: Natural Gas STAR reductions from gathering and boosting operations are reflected in the production sector.

## Vapor Recovery Units

- Methane Losses
- Methane Savings
- Is Recovery Profitable?
- Industry Experience
- Lessons Learned

## Sources of Methane Losses

- A storage tank battery can vent 5,000 to 500,000 thousand cubic feet (Mcf) of natural gas and light hydrocarbon vapors to the atmosphere each year
- Vapor losses are primarily a function of oil or condensate throughput, gravity, and gas-oil separator pressure
- Flash losses
- Occur when crude oil or condensate is transferred from a gas-oil separator at higher pressure to a storage tank at atmospheric pressure
- Working losses
- Occur when crude or condensate levels change and when liquid in tank is agitated
- Standing losses
- Occur with daily and seasonal temperature and barometric pressure changes

**Notes:**
Let’s first talk about methane losses from stock tanks.  There are 3 basic ways that methane is emitted from stock tanks:
Flashing – When gas evolves from crude oil when it transfers from a higher pressure vessel, such as a high pressure separator, to a lower pressure vessel, such as an atmospheric tank.  Gas entrained in the crude will come out of the fluid.
Working losses – Vapor losses that occur primarily due to the raising of tank levels and the agitation of the crude oil.
Standing losses – Occurs with crude oil static in the stock tanks.  Losses occur due to temperature and pressure changes in the environment; daily and seasonal.

## Methane Savings: Vapor Recovery

- Vapor recovery can capture up to 95% of hydrocarbon vapors from tanks
- Recovered vapors have higher heat content than pipeline quality natural gas
- Recovered vapors are more valuable than natural gas and have multiple uses
- Re-inject into sales pipeline
- Use as on-site fuel
- Send to processing plants for recovering valuable natural gas liquids

**Notes:**
Vapor Recovery Units are of great value because they are able to capture up to 95 percent of the hydrocarbon vapors that accumulate in storage tanks.  
Vapors can be more valuable than sales gas because they usually have a higher Btu content than pipeline quality natural gas.  The higher Btu content is the result of a natural refining process in which a lower pressure on the liquid crude allows some more complex hydrocarbon molecules to escape from the liquid and exist as components of the natural gas.
The higher Btu vapors can be extracted in the form of liquids and sold as separate products (such as propane, butane, ethane, etc.).  The value of these liquids, in addition to the value of the gas, depends on the demand for the specific product, but is generally more valuable than methane alone.

## Types of Vapor Recovery Units

- Conventional vapor recovery units (VRUs)
- Use screw or vane compressor to suck vapors out of atmospheric pressure storage tanks
- Scroll compressors are new to this market
- Require electrical power or engine driver
- Venturi ejector vapor recovery units (EVRUTM) or Vapor Jet
- Use Venturi jet ejectors in place of rotary compressors
- Contain no moving parts
- EVRUTM requires a source of high pressure motive gas and intermediate pressure discharge system
- Vapor Jet requires a high pressure water motive

**Notes:**
How many of you have VRUs operating in your fields or have had them in your areas before?

There are two basic types:
Conventional – use rotary compressors to remove vapors from tanks.  Require the use of electricity or a gas driver to operate.
Venturi Ejector VRU – (EVRU) and Vapor Jet – These use a Venturi tube instead of compressors to remove the gas from the tanks.  
There are no moving parts.
In the EVRU system there must be a source of high pressure gas and an intermediate pressure system to flow the gas / VRU gas.
Vapor Jet requires a high pressure water source.

## Conventional Vapor Recovery Unit

**Notes:**
This graph illustrates a VRU installed on a single crude oil storage tank (multiple tank installations are also common). 
Hydrocarbon vapors are drawn out of the storage (stock) tank under low pressure, typically between four ounces and two psi, and are first piped to a separator (suction scrubber) to collect any liquids that condense out. 
The liquids are usually recycled back to the storage tank. 
From the separator, the vapors flow through a compressor that provides the low pressure suction for the VRU system. (To prevent the creation of a vacuum in the top of a tank when oil is withdrawn and the oil level drops, VRUs are equipped with a control pilot to shut down the compressor and permit the back flow of vapors into the tank.) 
The vapors are then metered and removed from the VRU system for pipeline sale or on-site fuel supply.

## Vapor Recovery Installations

**Notes:**
Conventional VRU Installations

## Venturi Jet Ejector*

## Vapor Recovery with Ejector

- Mcf = Thousand cubic feet

**Notes:**
This is a very good overall view of the Venturi Jet Ejector system.

You can see the high pressure gas coming off downstream of the compressor, passing through the ejector to remove the vapors from the stock tank, then retuning upstream of the compressor to be compressed.

As this example illustrates, total production is 6.2 MMSCF/D at 1000 psig, the slipstream taken for the Venturi is 900 MCF/D, and with fuel gas removed (19 MCF/D) the total recovered gas from the tank is 281 MCF/D.  

The unit reduces the gas pressure from 1000 psig to 40 psig.

Eductors can be configured to work in parallel over a wide range of recovery rates with motive gas to vent ratios ranging from 3:1 to 7:1. This is really a niche VRU technology, it can only be used at facilities with high pressure motive gas and spare compressor capacity.

## Vapor Jet System*

- *Patented by Hy-Bon Engineering

**Notes:**
The Vapor Jet System utilizes a high pressure water stream instead of the high pressure gas stream to create the low pressure zone in the unit that will cause the vacuum to remove vapors from the crude oil stock tank.

The pressure readings shown are for a specific example.

## Vapor Jet System*

- *Patented by Hy-Bon Engineering

-  Utilizes produced water in closed loop system to effect gas gathering from tanks
-  Small centrifugal pump forces water into Venturi jet, creating vacuum effect
-  Limited to gas volumes of 77 Mcf/day and discharge pressure of 40 psig

**Notes:**
In the example above, the unit is using produced water in a closed loop for the Vapor Jet System.

Small pumps are used in this application to force the water into the Venturi Jets to create the vacuum.

The water and gas is piped to the separator, where the water and gas are separated.  The gas then is sent to sales and the water back to the stock tank.

In this particular example, with a specific Vapor Jet Unit, it is limited to 77 MCF/D of gas and a discharge pressure of 40 psig. 

The amount of gas recovered depends on the water pump sizing. Vapor Jets work well to recover relatively small volumes of tank vapors up to 77 Mcf/d. Again this is a niche technology that only works well for relatively small volumes of tank vapors and available produced water/electricity.

The pressure readings shown are for a specific example.

## Criteria for Vapor Recovery Unit Locations

- Steady source and sufficient quantity of losses
- Crude oil stock tank
- Flash tank, heater/treater, water skimmer vents
- Gas pneumatic controllers and pumps
- Dehydrator still vent
- Pig trap vent
- Outlet for recovered gas
- Access to low pressure gas pipeline, compressor suction, or on-site fuel system
- Tank batteries not subject to air regulations

**Notes:**
How do you chose a location to install a VRU?

The installation of a VRU can have a two-fold benefit:
It can be a profitable investment for the producer.
By reducing hazardous air pollutants (HAPs) below specified action levels, the investor can avoid the need to comply with certain state and federal regulations.

Realize a steady source and large enough volume of losses from production equipment, tanks, flash tanks, heater treaters, water skimmers, pneumatic controllers, and pumps.

There is an outlet for the recovered gas, access to a low or intermediate pressure gas system, compressor suction, or use for fuel onsite.

Tank batteries not already subject to air regulations.

Gas STAR Partners can only receive emission savings credit for installation of VRUs where they are not required to by law. The point here is that they should be looking to install VRUs beyond the locations where they are required to do so.

## Quantify Volume of Losses

- Estimate losses from chart based on oil characteristics, pressure, and temperature at each location (± 50%)
- Estimate emissions using the E&P Tank Model (± 20%)
- Engineering Equations – Vasquez Beggs (± 20%)
- Measure losses using recording manometer and well tester or ultrasonic meter over several cycles (± 5%)
- This is the best approach for facility design

**Notes:**
How do you quantify potential losses from production equipment – especially storage tank vapors?

Of the first two methods, using the chart (see next slide) is quicker and can have a high level of accuracy since it is developed using actual field data.

The E&P Tank model was developed by the American Petroleum Institute and the Gas Research Institute to give a greater magnitude of accuracy by computerizing the mathematical calculations from the field data and avoiding interpretation problems associated with the chart.

The Vasquez-Breggs Equations directly calculate Gas-Oil ratios (GOR’s) for tank losses

Then there is the direct measurement method – I have done this and it takes a while, and must be carefully done to obtain correct data.  It is the best approach because it provides the data for your specific application.

## Estimated Volume of Tank Vapors

- Pressure of Vessel Dumping to Tank  (Psig)

- Vapor Vented from Tanks,
- cubic foot / barrel
- Gas/Oil Ratio

- 110

- 100

- 90

- 80

- 70

- 60

- 50

- 40

- 30

- 10

- 20

- 10

- 20

- 30

- 40

- 50

- 60

- 70

- 80

**Under 30° API**

**30° API to 39° API**

**40° API and Over**

- o API = API gravity

- API Gravities

**Notes:**
This is an example of using a chart to estimate the vapor emitted from the tank, in cubic feet per barrel.

As you can see, the API gravities for the oil in the tank are lumped into 3 categories, Under 30 deg API, 30 – 40 deg API, and over 40 deg API.  If you have additional granularity in the chart, you will have greater accuracy.

Let’s say you have a separator dumping crude oil to the tank at 35 psig, at a crude oil gravity of 35 deg API.  If the API gravity is actually 32 or 38 you will have to interpolate the results on the graph grid.

Draw a line up from the x-axis at 35 psig, move up to the API gravity line, move across to the y axis, and you note that the vapor vented from the tanks is 40 cubic feet per barrel.

If the separator flows 250 barrels per day to the tank, that’s 10 MCF of gas emitted.

## Atmospheric tanks may emit large amounts of tank vapors at relatively low separator pressure

- Atmospheric tanks may emit large amounts of tank vapors at relatively low separator pressure

**Vasquez-Beggs Equation**

- psig – pounds per square inch, gauge
- scf – standard cubic feet
- bbl – barrels

## What is the Recovered Gas Worth?

- Value depends on heat content of gas
- Value depends on how gas is used
- On-site fuel
- Valued in terms of fuel that is replaced
- Natural gas pipeline
- Measured by the higher price for rich (higher heat content) gas
- Gas processing plant
- Measured by value of natural gas liquids and methane, which can be separated
- Gross revenue per year = (Q x P x 365) + NGL
- Q = Rate of vapor recovery (Mcf per day)
- P = Price of natural gas
- NGL = Value of natural gas liquids

**Notes:**
So is recovery of the stock tank vapors profitable?

The use of recovered gas as an on-site fuel can offset the retail cost of fuel and the cost of transportation to the site.

Natural gas is now sold by the energy content (Btu), not volume (Mcf).  Rich gas demands a higher price from both pipelines and processing plants.

## Value of Natural Gas Liquids

|  | 5Btu/cf | 6MMBtu/Mcf | 7$/Mcf(=4*6) | 8$/MMBtu | 9Vapor Composition | 10Mixture(MMBtu/Mcf) | 11Value($/Mcf)(=8*10) |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Methane | 1,012 | 1.01 | $7.22 | 7.15 | 82% | 0.83 | $5.93 |
| Ethane | 1,773 | 1.77 | $38.18 | 21.57 | 8% | 0.14 | $3.05 |
| Propane | 2,524 | 2.52 | $55.71 | 22.11 | 4% | 0.10 | $2.23 |
| n Butane | 3,271 | 3.27 | $81.09 | 24.80 | 3% | 0.10 | $2.43 |
| iso Butane | 3,261 | 3.26 | $80.90 | 24.90 | 1% | 0.03 | $0.81 |
| Pentanes+ | 4,380 | 4.38 | $122.64 | 28.00 | 2% | 0.09 | $2.45 |
| Total |  |  |  |  |  | 1.289 | $16.90 |

|  | 1Btu/gallon | 2MMBtu/ gallon | 3$/gallon | 4$/MMBtu1,2 (=3/2) |
| --- | --- | --- | --- | --- |
| Methane | 59,755 | 0.06 | 0.43 | 7.15 |
| Ethane | 74,010 | 0.07 | 1.51 | 21.57 |
| Propane | 91,740 | 0.09 | 1.99 | 22.11 |
| n Butane | 103,787 | 0.10 | 2.48 | 24.80 |
| iso Butane | 100,176 | 0.10 | 2.49 | 24.90 |
| Pentanes+* | 105,000 | 0.11 | 3.08 | 28.00 |
|  |  |  |  |  |

**1 – Natural Gas Price assumed at $7.15/MMBtu as on Mar 16, 2006 at Henry Hub****2 – Prices of Individual NGL components are from Platts Oilgram for Mont Belvieu, TX July 11, 2008**

**Notes:**
So is recovery of the stock tank vapors profitable?

Let’s begin by looking at the value of the higher BTU content gas – at a BTU / MCF much high than methane, the value per MCF is around $16.90 / MCF.

Pentane+ is assumed to be that of natural gasoline LDH for Mont Belvieu from Platts.

## Cost of a Conventional VRU

| Vapor Recovery Unit Sizes and Costs |  |  |  |  |
| --- | --- | --- | --- | --- |
| Capacity (Mcf/day) | Compressor Horsepower | Capital Costs ($) | Installation Costs ($) | O&M Costs ($/year) |
| 25 | 5 to 10 | 20,421 | 10,207 to 20,421 | 7,367 |
| 50 | 10 to 15 | 26,327 | 13,164 to 26,327 | 8,419 |
| 100 | 15 to 25 | 31,728 | 15,864 to 31,728 | 10,103 |
| 200 | 30 to 50 | 42,529 | 21,264 to 42,529 | 11,787 |
| 500 | 60 to 80 | 59,405 | 29,703 to 59,405 | 16,839 |
| Cost information provided by United States Natural Gas STAR companies and VRU manufacturers, 2006 basis.  |  |  |  |  |

**Notes:**
This table looks shows that the capital and operating costs for a VRU are not linear, you do realize economies of scale.

Adapted from the VRU Lessons Learned, page 8, exhibit 6.  Using the vapor dollar value from slide 19; NPV = costs/annual savings*12months; ROI = annual savings/costs.

## Is Recovery Profitable?

| Financial Analysis for a Conventional VRU Project |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- |
| Peak Capacity (Mcf/day) | Installation & Capital Costs1 ($) | O&M Costs ($/year) | Value of Gas2 ($/year) | Annual Savings 
($) | Simple Payback (months) | Internal Rate of Return |
| 25 | $35,738 | $7,367 | $77,106 | $69,739 | 10 | 121% |
| 50 | $46,073 | $8,419 | $154,213 | $145,794 | 6 | 204% |
| 100 | $55,524 | $10,103 | $308,425 | $298,322 | 4 | 352% |
| 200 | $74,425 | $11,787 | $616,850 | $605,063 | 3 | 537% |
| 500 | $103,959 | $16,839 | $1,542,125 | $1,525,286 | 2 | 974% |
| 1 – Unit cost plus estimated installation of 75% of unit cost2 – $16.90 x 1⁄2 peak capacity x 365, Assumed price includes Btu enriched gas (1.289 MMBtu/Mcf) |  |  |  |  |  |  |

**Notes:**
This table looks at several possible scenarios of peak capacity for VRU sizing, from 25 MCF / D to 500 MCF / D (VRUs are sized for 2X stock tank vapor emissions expected – they do not run 100% of the time).

It’s very easy to see that as the volume of recovered vapor increases, the annual savings increases  - the simple payback improves with increases in vapor recovery as does the IRR.

Adapted from the VRU Lessons Learned, page 8, exhibit 6.  Using the vapor dollar value from slide 19; IRR calculated over a 5-year period.

## Industry Experience: EnCana Oil & Gas

- Vapor recovery unit installed in Frenchie Draw, WY
- Captures vapors from
- Separators
- Crude oil storage tank
- Non-condensable dehydrator still gas
- VRU designed to handle 500 Mcf/day
- Additional capacity over the estimated 284 Mcf/day of total gas from all emission sources

## Industry Experience: EnCana Oil & Gas

- Quantify the volume of vapor emissions

**Total Emissions-    284 MSCFD**

- Source: EnCana Oil & Gas (USA) Inc.

## EnCana Oil & Gas: Project Costs

- Determine the cost of VRU project

_***Installation***_
- VRU Unit (500 Mcfd) - 	 	 $90,000
- Generator-			 $85,000
- Vent Header-			 $25,000
- Labor-			            _$200,000_
- TOTAL  		            $400,000
_***O & M***_
- VRU Unit (500 Mcfd) - 	 	 $15,000
- Generator-			 $18,000
- Fuel-				 _$73,000_
- TOTAL  		            $106,000

## EnCana Oil & Gas: Project Economics

- Evaluate VRU economics

- Capacity–		             500 Mcfd
- Installation Cost - 		$400,000
- O&M-			             $106,000/year
- Value of Gas*-			$788,400/year
- Payback-		             7 months
- Return on Investment-                170%

- *Gas price assumed to be $ 7.60 by Encana

## Industry Experience: Anadarko

- Vapor Recover Tower (VRT)
- Add separation vessel between heater treater or low pressure separator and storage tanks that operates at or near atmospheric pressure
- Operating pressure range: 1 psi to 5 psi
- Compressor (VRU) is used to capture gas from VRT
- Oil/Condensate gravity flows from VRT to storage tanks
- VRT insulates the VRU from gas surges with stock tank level changes
- VRT more tolerant to higher and lower pressures
- Stable pressure allows better operating factor for VRU

## Industry Experience: Anadarko

- VRT reduces pressure drop from approximately 50 psig to 1-5 psig
- Reduces flashing losses
- Captures more product for sales
- Anadarko netted between $7 to $8 million from 1993 to 1999 by utilizing VRT/VRU configuration
- Equipment Capital Cost: $11,000
- Standard size VRTs available based on oil production rate
- 20” x 35’
- 48” x 35’
- Anadarko has installed over 300 VRT/VRUs since 1993 and continues on an as needed basis

## VRT/VRU Photos

- Courtesy of Anadarko

## Vapor recovery can yield generous returns when there are market outlets for recovered gas
Recovered high heat content gas has extra value
Vapor recovery technology can be highly cost-effective in most general applications
Venturi jet models work well in certain niche applications, with reduced operating and maintenance costs
Potential for reduced compliance costs can be considered when evaluating economics of VRU, EVRUTM, or Vapor Jet

- Vapor recovery can yield generous returns when there are market outlets for recovered gas
- Recovered high heat content gas has extra value
- Vapor recovery technology can be highly cost-effective in most general applications
- Venturi jet models work well in certain niche applications, with reduced operating and maintenance costs
- Potential for reduced compliance costs can be considered when evaluating economics of VRU, EVRUTM, or Vapor Jet

## VRU should be sized for maximum volume expected from storage tanks (rule-of-thumb is to double daily average volume)
Rotary vane, screw or scroll type compressors recommended for VRUs where Venturi ejector jet designs are not applicable
EVRUTM recommended where there is a high pressure gas compressor with excess capacity
Vapor Jet recommended where there is produced water, less than 75 Mcf per day gas and discharge pressures below 40 psig

- VRU should be sized for maximum volume expected from storage tanks (rule-of-thumb is to double daily average volume)
- Rotary vane, screw or scroll type compressors recommended for VRUs where Venturi ejector jet designs are not applicable
- EVRUTM recommended where there is a high pressure gas compressor with excess capacity
- Vapor Jet recommended where there is produced water, less than 75 Mcf per day gas and discharge pressures below 40 psig

## Gas lost when launching and receiving a pig
Fugitive emissions from pig launcher/receiver valves
Gas lost from storage tanks receiving condensate removed by pigging
Gas vented from pipeline blowdowns

- Gas lost when launching and receiving a pig
- Fugitive emissions from pig launcher/receiver valves
- Gas lost from storage tanks receiving condensate removed by pigging
- Gas vented from pipeline blowdowns

**Notes:**
EFs from the natural gas systems inventory, 1990 to 2005

## Hydrocarbons and water condense inside pipelines, causing pressure drop and reducing gas flow
Periodic line pigging removes liquids and debris to improve gas flow
Also inspect pipeline integrity
Efficient pigging:
Keeps pipeline running continuously
Keeps pipeline near maximum throughput by removing debris
Minimizes product losses during launch/capture

- Hydrocarbons and water condense inside pipelines, causing pressure drop and reducing gas flow
- Periodic line pigging removes liquids and debris to improve gas flow
- Also inspect pipeline integrity
- Efficient pigging:
- Keeps pipeline running continuously
- Keeps pipeline near maximum throughput by removing debris
- Minimizes product losses during launch/capture

- Source: www.girardind.com/

## Pig launchers have isolation valves for loading pigs, pressurizing pigs, and launching pigs with gas bypassed from the pipeline
Launcher pressuring/depressuring loses methane out the vent valve

- Pig launchers have isolation valves for loading pigs, pressurizing pigs, and launching pigs with gas bypassed from the pipeline
- Launcher pressuring/depressuring loses methane out the vent valve

## Methane lost through vent valve on the launcher and again through vent valve on the receiver
Once receiver is isolated from the line, it must be depressured to remove the pig
Liquids ahead of the pig drain to a vessel or tank
MORE than twice: isolation valve leaks may cause excessive venting                                                       to depressure

- Methane lost through vent valve on the launcher and again through vent valve on the receiver
- Once receiver is isolated from the line, it must be depressured to remove the pig
- Liquids ahead of the pig drain to a vessel or tank
_*MORE than twice*_*:* isolation valve leaks may cause excessive venting                                                       to depressure

- Source: www.girardind.com/

**Notes:**
Depending on the company practices, a launcher will remain pressurized or they will depressurize it. Fugitives should be a lot less in the latter case.

## Pipeline maintenance requires pipe section blowdown before work can begin
Gas in pipeline is usually vented to the atmosphere
Use inert gas and pig
Route vent to vapor recovery system or fuel gas
One Partner reported connecting pig receiver vent to fuel gas to recover gas while working a tight isolation

- Pipeline maintenance requires pipe section blowdown before work can begin
- Gas in pipeline is usually vented to the atmosphere
- Use inert gas and pig
- Route vent to vapor recovery system or fuel gas
- One Partner reported connecting pig receiver vent to fuel gas to recover gas while working a tight isolation

**Notes:**
--Inert gas can be used to drive a pig down the section of pipe to be serviced, displacing the natural gas to a product line rather than venting
--Inert gas is then vented to the atmosphere, avoiding methane loss

## Is Recovery Profitable?

- One partner pigged gathering lines 30 to 40 times per year, collecting several thousand barrels of condensate per application
- Partner reported saving 21,400 Mcf/year from recovering flash gases
- Dedicated vapor recovery unit (VRU) was installed with an electric compressor at an installation cost of $24,000 and an annual operating cost of $40,000 mostly for electricity
- Large gas savings and increasing gas prices will offset costs

| Gas Price ($/Mcf) | $7.00 |
| --- | --- |
| Gas Saved (Mcf/year) | 21,400 |
| Annual Savings ($/year) | $149,800 |
| Installed Cost | $24,000 |
| Operating Cost | $40,000 |
| Payback Period (years) | 0.3 |

**Notes:**
Compiled from April 22nd, 2005 Oklahoma City Presenentation and  2003 Annual Reports – GulfTerra reported saving 21,400 Mcf/year from recovering flash gases from condensate.

## Discussion

- Industry experience applying these technologies and practices
- Limitations on application of these technologies an practices
- Actual costs and benefits