Installing Plunger Lift Systems In Gas Wells
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)
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
= gas production rate
= absolute temperature
= formation height
= external boundary radius
= wellbore radius
= 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
This is a guideline, and operators
reminded to use determination.
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,
and 284). If
vent the wells
a longer time
these methods, the be increased by a
conservative Annual simple ratio of the
actual vent times and the minimum using the Weymouth equation.
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