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Installing Plunger Lift Systems In Gas Wells

(Cont’d)

average peak production rate after liquids unloading. This is assumed to be equal to the potential peak production rate that could be achieved with a plunger lift system, typically at least 80 percent of

the

peak

production

rate

after

blowdown.

The

shaded

area

between

the

potential

production

into account other financial benefits of a plunger lift installation project, such as avoided emissions and decreased electricity and chemical treatment costs, which are described later in this Lessons Learned. Consideration of these additional benefits may improve the already excellent financial returns of a plunger lift installation.

line) represents the estimate of incremental increase in gas production that can be achieved with a

Revenue from Avoided Emissions

plunger lift system.

Estimating incremental

production

for

declining wells or for situations in which the maximum production level after blowdown is not known. Wells that are in decline or operated without periodic blowdowns require more detailed

methods for plunger lift

estimating systems.

incremental production under Plunger lift installations on

declining

wells,

for

example,

will

require

generating

an

improved

declining

curve

resulting

from

decreased

pressure at perforations. Operators assistance of a reservoir engineer determinations (see Appendix).

should to aid

seek the in these

The amount of natural gas emissions reduced following plunger lift installation will vary greatly from well to well, based on the individual well and reservoir characteristics such as sales line pressure, well shut-in pressure, liquids accumulation rate, and well dimensions (depth, casing diameter, tubing diameter). The most important variable, however, is the normal operating practice of venting wells. Some operators put wells on automatic vent timers, while others manually vent the wells with the operator standing by monitoring the vent, and still others open the well vent and leave, returning in hours or up to days, depending on how long it typically takes the well to clear liquids. Thus, the economic benefits from avoided emissions will also vary considerably. Such wide variability means that some

Incremental Gas Production (Mcfd)

Payout Time (months)

Internal Rate of Return (%)

3 5 10 15 20 25 30

14 8 4 3 2 2 2

71 141 309 475 640 804 969

Once incremental production from a plunger lift installation is estimated, operators can calculate the value of incremental gas and estimate the economics of the plunger lift installation. Exhibit 4 presents an example of potential financial returns at different levels of increase in gas production. It is important to recognize that local costs and conditions may vary. Note also that the example in Exhibit 4 does not take

Exhibit 4: Example of Estimated Financial Returns for Various Levels of Incremental Gas Production from a Plunger Installation

Assumptions: Value of gas = $7.00/Mcf. Plunger system cost of $7,772 including start-up cost. Lease operating expense of $790/year. Production decline of 6%/year.

Source: Production Control Services, Inc.

projects others.

will have much shorter payback periods than While most plunger lift installations will be

justified by increased emissions reductions stream.

gas production rates alone, can provide an additional

methane revenue

Avoided emissions when replacing blowdowns. In wells where plunger lift systems are installed,

emissions reduced.

from blowing down the well Blowdown emissions vary widely

can be in both

their frequency and flow and reservoir specific.

rates and are entirely well Emissions attributable to

blowdown per year

activities have been reported from 1 Mcf to thousands of Mcf per year per well.

Therefore, the savings attributable emissions will vary greatly based on the particular well being rehauled.

to avoided data for the

Revenue from avoided emissions can be calculated by multiplying the market value of the gas by the volume of avoided emissions. If the emissions per well per blowdown have not been measured, they

must be estimated. amount of gas that is

In the example below, vented from a low pressure

the gas

well

at

each

blowdown

is

estimated

as

0.5625

times

the sustained

flow gas rate.

assumes that

the integrated

This emission factor average flow over the

blowdown Using this

period is 56.25 percent of full well flow. assumption, Exhibit 5 demonstrates that

5

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