Methods for Improving Gas Lift Efficiency in Large...

Gas Well Deliquification Workshop

Sheraton Hotel, Denver, Colorado

February 23 – 25, 2015

Methods for Improving Gas Lift Efficiency in Large Systems

Ross Moffett, Applications Engineer

Weatherford Production Optimization Systems

Feb. 23 - 25, 2015

2015 Gas Well Deliquification Workshop

Denver, Colorado

2

What is meant by improving efficiency?

Efficiency: the ratio of the useful work

performed by a machine or in a

process to the total energy expended

or heat taken in.

•Spend as little money as possible

while producing the same outcome

as before

• Improve upon prior results if possible

Feb. 23 - 25, 2015 2015 Gas Well Deliquification Workshop

Denver, Colorado

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Outline

• Define Gas Lift

• Describe a variety of common installations

• Review advantages/disadvantages of each type

• Review methods of overcoming disadvantages using

automated equipment

• Common challenges encountered while automating

gas lift sites

Feb. 23 - 25, 2015


Denver, Colorado

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What is Gas Lift?

Gas is injected into Casing Annulus

• Strategically placed gas lift valves

allow gas into the tubing at set

pressures

• Gas forces fluid up the tubing stage

by stage

• As the further downhole stages are

opened, higher stages close

• Upon unloading, only the bottom gas

lift valve is used

Feb. 23 - 25, 2015


Denver, Colorado

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Typical Single Well Gas Lift System (Assumes no Oil)

Instrumentation

• Casing

Pressure

• Tubing

Pressure

• Injection Rate

• Flowline

Pressure

• Flowline Temp

(Optional)


Denver, Colorado

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Advantages of Single Well Automated System

• Gas injection rate or pressure may be remotely

adjusted according to changing process

conditions to improve well performance (i.e.

correcting over-injection, which causes

reduced production by backpressure or

correcting under-injection, which causes

intermittent flow from the well)

• Remote shut-downs for suspected

environmental risks, auditing of flow volumes

and fluid inventory

Feb. 23 - 25, 2015


Denver, Colorado

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Simple Automated Gas Lift System

RTU/PLC

• Gas Lift

Injection Flow

Measurement

• Gas Lift

Injection Rate

Control

• Two Wells

Sharing Single

Compression

Source

< Well1 < Well2

Compressor


Denver, Colorado

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Advantages of Simple Automated System

Increased production during non-optimal conditions

• Gas can be evenly or unevenly distributed to the wells

as its availability changes and according to which well

uses it more effectively

• After a compressor shut-down has been repaired, the

loaded wells can be taken back online one at a time

without supervision

• Reduced monthly rental fees from sharing the

compression source

• Pressure overrides may be used to take control of

abnormal conditions

Feb. 23 - 25, 2015


Denver, Colorado

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Multi-Well Pad With Duplication

Built exactly

the same

as a single-

well pad,

but with

like

equipment

grouped in

rows


Denver, Colorado

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Why not share equipment in large multi-well pads?

• Downtime due to equipment malfunction

limited to single wells

• Easier to account for fluid production by

separating liquid streams to dedicated

tanks & truck loading tickets per well

• Lower risk of insufficient compression

source

• Lower complexity of installation


Denver, Colorado

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Why have large gas lift systems with shared equipment?

Higher capital efficiency in drilling multi-well pads

• Shared separation resources

• Shared storage tanks

• Shared gas lift source

• Smaller well plot

• Primary cost savings are unrelated to production

optimization and based on cost of production process

equipment (capital efficiency)

• Can be hundreds of thousands or millons of dollars per

pad


Denver, Colorado

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Case in point: Compressor Rental

Assuming 6 well pad with $2500/mo rental fee

• 6 compressors * $2500 * 12 months = $180,000

Reduce to 3 compressors, with associated automation

costing <$60,000

• 3 compressors * $2500 * 12 months = $90,000

• $90,000 + $60,000 = $150,000

• Saved $30k in first year, also includes full tank level,

flow and pressure monitoring with locally controlled

emergency shut-down valves

Feb. 23 - 25, 2015


Denver, Colorado

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Large Automated Gas Lift System

• Central

Facility

• Multi-well

pads

• Shared

resources

• Well

Testing

• Control

Valves

3-well

Pad 3-well

Pad

3-well

Pad

Shared separation

equipment with

individual well test

separator

Shared gas lift

compressor(s)

Shared flaring & tanks off-screen


Denver, Colorado

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Problems with large gas lift systems

Process disruptions may affect many wells at

once

• Shared compressor(s) going down

• One poorly optimized well causes others to

lose production

• Bringing a new well online is taxing to the

overall system

• Production equipment is more complicated


Denver, Colorado

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Solving Problems with gas lift systems

API RP 11V5

• This document from the API outlines ways to properly

respond and operate during different sorts of gas lift

issues

• With automation, the practices may be made to be

automatic, saving valuable field time

• Using well simulation software, the gas allocations can

be virtually re-allocated by computing systems in order

to find the exact optimal rate of injection for each well

given gas source limitations. This requires logging of

all of the variables detailed in the single well slide.


Denver, Colorado

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Advantages of Large Automated System

Same advantages of a simple system, plus:

• Ability to shut down all remote sites in case of

impending catastrophe (high tank levels, dangerous

pressure build-up, leak detection)

• Ability to centrally monitor and control remote wells

with or without using SCADA

• Lower cost of separation and allocations metering due

to shared separation resources

• For multiple compressor systems, a single compressor

going down will automatically cause lower-producing

wells to disable gas-lift and shut-in until pressure is re-

established.


Denver, Colorado

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Automated Mechanics of Operation

During Unloading

• Running fluid through

downhole gas lift valves

at high rates will destroy

(“cut”) the valves

• To reduce the chances of

“cutting” the valve

orifice(s), the gas

injection pressure is

slowly ramped at a fixed

rate

Feb. 23 - 25, 2015


Denver, Colorado

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Automatic

determination of

completed unloading

• When the tubing

pressure shows

evidence of

complete unloading,

transition to a

constant

rate/pressure

injection control


Denver, Colorado

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During Run-Auto

• Maintain constant injection rate

• Override valve position if injection pressure falls out of

specification (too high)

• If injection pressure falls too low, shut off injection to

weak wells

• As injection pressure returns (re-started compressor,

increased gas supply, etc) begin turning on shut-in

wells again. Use the well pressures to actuate the

choke valve using pressure reducing control to avoid

hazards at the separator.


Denver, Colorado

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During any stage

• Monitor tank levels and shut in

remote wells on high level

• Monitor pressures at different

production equipment stages and

shut-in wells individually or in

groups as required


Denver, Colorado

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Using SCADA to Optimize Injection

Many areas do not have access to sufficient lift gas to

inject optimal rates

• Use SCADA system to gather historical

pressure/temperature/flow data and build well models

based on this data

• Compare produced volumes from well testing

apparatus to injected rates & pressures, run analysis in

well model to seek production improvements

• Re-allocate the gas lift injection rates daily to favor

wells who produce the most cash value with the

available gas


Denver, Colorado

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Issues thus far

Usually deployment problems are related to production

equipment or process issues

• Insufficient gas supply interrupts proper deployment of

API RP unloading procedure

• Undersized or problematic high pressure bypass

valves on compressor discharge cause compressor

shutdowns

• Improper sizing of rate control chokes inner valve

orifice may cause poor performance (swinging rates or

pressures)

• Deployments tested in Oklahoma and South Texas


Denver, Colorado

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Questions?

Ross Moffett Applications Engineer Weatherford Production Optimization Systems

[email protected]


Denver, Colorado

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Copyright

Rights to this presentation are owned by the company(ies) and/or author(s) listed on the title page. By submitting this presentation to the Gas Well Deliquification Workshop, they grant to the Workshop, the Artificial Lift Research and Development Council (ALRDC), and the Southwestern Petroleum Short Course (SWPSC), rights to:

– Display the presentation at the Workshop.

– Place it on the www.alrdc.com web site, with access to the site to be as directed by the Workshop Steering Committee.

– Place it on a CD for distribution and/or sale as directed by the Workshop Steering Committee.

Other use of this presentation is prohibited without the expressed written permission of the author(s). The owner company(ies) and/or author(s) may publish this material in other journals or magazines if they refer to the Gas Well Deliquification Workshop where it was first presented.


Denver, Colorado

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Disclaimer

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The Artificial Lift Research and Development Council and its officers and trustees, and the Gas Well Deliquification Workshop Steering Committee members, and their supporting organizations and companies (here-in-after referred to as the Sponsoring Organizations), and the author(s) of this Technical Presentation or Continuing Education Training Course and their company(ies), provide this presentation and/or training material at the Gas Well Deliquification Workshop "as is" without any warranty of any kind, express or implied, as to the accuracy of the information or the products or services referred to by any presenter (in so far as such warranties may be excluded under any relevant law) and these members and their companies will not be liable for unlawful actions and any losses or damage that may result from use of any presentation as a consequence of any inaccuracies in, or any omission from, the information which therein may be contained.

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