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Installing Plunger Lift Systems In Gas Wells

(Cont’d)

Appendix

Estimating incremental production for declining wells.

and shut-in pressure is in psig. example calculation.

Exhibit A1 shows an

From Dake’s Fundamentals of Reservoir Engineering (1982) we can use the following equation to calculate the increase in downhole flow for reduced pressure that may

be seen when using a plunger lift. inflow equation can be expressed as:

A semi-steady state

Exhibit A1: Example—Estimate Avoided Emissions from Blowdowns

m(pavg) - m(pwf) = [(1422 × Q × T)/(k × h)] × [ln(re/rw 3/4+S)] × (8.15)

Casing Diameter

8 inches

Well Depth

10,000 feet

Where,

Shut-in Pressure

214.7 psig

Annual Vents

52 (weekly venting)

m(pavg) = real gas pseudo pressure average

m(pwf) = real gas pseudo pressure well flowing

Annual Vent Volume = (0.37 x 10-6) x 82 x 10,000 x 214.7 x 52 = 2,644 Mscf/yr

Q

= gas production rate

T

= absolute temperature

k

= permeability

h

= formation height

re

= external boundary radius

rw

= wellbore radius

S

= mechanical skin factor

After the reservoir parameters are gathered, this equation can be solved for Q for the retarded flow with fluids in the hole (current conditions and current decline curve), and Q for no fluids in the hole (plunger lift active and improved

decline curve).

This is a guideline, and operators

reminded to use determination.

a

reservoir

engineer

to

aid

in

are this

This is the minimum volume of gas that would be vented to atmospheric pressure from a well that has stopped flowing to the sales line because a head of liquid has accumulated in the tubing equal to the pressure difference between the sales line pressure and well shut-in pressure. If the well shut-in pressure is more than 1.5 times the sales line pressure, as required for a plunger lift installation in Exhibit 2, then the volume of gas in the well casing at shut-in pressure should be minimally sufficient to push the liquid in the tubing to the surface in slug-flow when back-pressure is reduced to zero psig. Partners can estimate the minimum time to vent the well by using this volume and the Weymouth gas-flow formula (worked out for common pipe diameters, lengths and pressure drops in Tables 3, 4 and 5 in Pipeline Rules of Thumb Handbook,

Fourth

Edition, pages

283

and 284). If

the Partner’s

practice

and experience

is to

vent the wells

a longer time

than

calculated by

Vent

Volume can

these methods, the be increased by a

conservative Annual simple ratio of the

actual vent times and the minimum using the Weymouth equation.

vent

time

calculated

Alternate technique for calculating avoided emissions when replacing blowdowns.

A conservative estimate of well venting volumes can be made using the following equation:

Annual Vent Volume, Mscf/yr = (0.37×10-6) × (Casing Diameter)2 × Well Depth × Shut-in Pressure × Annual Vents

Where casing diameter is in inches, well depth is in feet

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