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Installing Plunger Lift Systems In Gas Wells

(Cont’d)

for an unloaded well producing 100 Mcf per day, the gas vented to the atmosphere can be estimated at 2 Mcf per hour of blowdown.

Exhibit 5: Example—Estimate Avoided Emissions from Blowdowns

Avoided Emissions per Hour of

= (0.56251 x Sustained Daily Flow

Blowdowna Avoided Emissionsb

Annual Value of Avoided Emissionsc

Rate) / 24 hrs/day

= (0.5625 x 100 Mcfd) / 24 = 2 Mcf per hour of blowdown = 2 Mcf x 12 x $7.00/Mcf = $168 per year

Recommended methane emission factor reported in the joint GRI/EPA study, Methane Emissions From the Natural Gas Industry, Volume 7: Blow and Purge Activities (June 1995). The study estimated that at the beginning of a blowdown event, gas flow is restricted by fluids in the well to 25 percent of full flow. By the end of the blowdown event, gas flow is returned to 100 percent. The integrated average flow over the blowdown period is 56.25 percent of full well flow. a

b c

Assuming a sustained daily production rate of 100 Mcfd. Assuming 1 blowdown per month lasting 1 hour.

This method is simple to use, but anecdotal evidence

suggests that it produces estimates of emissions avoided that are unrealistically

an

alternate

method

for

estimating

methane low. For avoided

Avoided well treatment costs are applicable when plunger lifts replace beam lifts or other remedial techniques such as blowdown, swabbing, or soaping. Reduced electricity costs, reduced workovers, and recovered salvage value are only applicable if plunger lifts replace beam lifts.

dispersants,

hot

fluids,

crystal

modifiers,

and

surfactants)

are

reported

in the

literature

at a

costs. Well treatment treatments, microbial rods and scraping the shallow 1,500-foot wells

show

well

remediation

costs

including

rod

removal

minimum of $13,200 per well per year. costs to reduce paraffin have been shown to

Microbial be $6,600

Avoided well

treatment

costs

include

chemical

cleanups,

and removal of

borehole.

Information from

at

more

than

$14,500

per

costs (inhibitors, solvents,

treatments do Each of these

treatment costs increases as the severity or paraffin increases, and as the depth increases.

of

the scale

of

the well

and

tubing

rehabilitation

well.

Chemical

treatment

microbial problem).

per not

well per year (note that address the fluids influx

emissions from blowdowns, see the Appendix.

Reduced electricity costs compared to beam

lifts.

Reduced

electric

operating

costs

further

Given the high degree of variability in emissions

increase

the

economic

return

of

plunger

lifts.

No

based on well measurement

and

reservoir specific

characteristics,

is

the

preferred

method for

determining avoided emissions.

Field measurements

can

provide

the

data

necessary

to

accurately

electrical

costs

are

associated

with

plunger

lifts,

because battery avoided

most controllers are solar-powered with backup. Exhibit 6 presents a range of electricity costs reported by operators who

determine emissions.

the

savings

attributable

to

avoided

have installed plunger lifts. operation, avoided electricity to $7,300 per year.

Assuming costs range

365 days of from $1,000

Avoided emissions when replacing beam lifts. In cases where plunger lifts replace beam lifts rather than blowdowns, emissions will be avoided due to reduced workovers for mechanical repairs, to remove debris and cleanout perforations, to remove mineral scale and paraffin deposits from the sucker rods. The average emissions associated with workovers have

Reduced workover costs compared to beam

lifts. been

Workover costs associated with reported as $1,300 per day.

beam lifts have While typical

Exhibit 6: Electricity Costsa Avoided by Using a Plunger Lift in Place of a Beam Lift

been reported the frequency range from 1

as approximately 2 Mcf per workover;

of to

workovers has been

15

per

year.

Due

to

reported to well-specific

characteristics such as flow during duration of workover, and frequency of avoided emissions can vary greatly.

workover, workover,

Avoided Costs and Additional Benefits

Avoided costs depend on the type of liquid removal systems currently in place, but can include avoided well treatment, reduced electricity costs, and reduced workover costs.

Motor Size (BHP)

Operation Cost ($/day)

10

3

20

7

30

10

40

13

50

17

60

20

Electricity cost assumes 50 percent of full load, running 50 percent of the time, with cost of 7.5 cents/ kWh. a

6

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