Gas Lift Valve Spacing Formula

Gas lift is an artificial lift method where compressed gas is injected into the production tubing to reduce the hydrostatic head of the fluid column, thereby allowing reservoir pressure to push fluids to the surface. Gas lift valve spacing determines the depth and opening pressures of each valve to ...

Overview

Theory

Gas lift valve spacing follows a systematic procedure:

Start at the surface with a known kickoff pressure
Each successive valve is placed where the injection gas pressure in the annulus can open the valve while the tubing pressure allows flow
A design pressure drop (ΔP per valve) ensures positive downward progression
The deepest valve (operating valve) injects gas continuously at the design point

Formulas

Gas Lift Valve Opening Pressure (Casing Operated, Bellows Charged)

Pvo = Pb * (1 - Ab/Ap) + Pt * (Ab/Ap)

where Pvo = valve opening pressure, Pb = bellows charge pressure (at depth temperature), Ab = bellows area, Ap = port area, Pt = tubing pressure at valve depth.

Test Rack Opening Pressure (TROP)

TROP = Pvo * (Tsurf / Tvalve) * Ct

where Ct = temperature correction factor for nitrogen charge.

Injection Pressure at Depth

Pinj_depth = Pinj_surface * exp(0.01875 * γg * TVD / (Tavg * Zavg))

(Gas column pressure calculation using gas gravity.)

Unloading Gradient

Kill_fluid_gradient = 0.052 * ρ_kill  (psi/ft)
Design_gradient = Kill_fluid_gradient - ΔP_design / interval

Valve Spacing — Graphical Method

Plot injection gas pressure line (surface to TD)
Plot kill fluid gradient from surface
First valve: intersection of kill fluid line with injection pressure minus design ΔP
Each subsequent valve: draw production gradient from previous valve depth to new intersection

Gas Lift Performance (GLR Effect)

qL = f(GLR, Pwf, WHP, tubing size) — from VLP/TPC curves

Optimum GLR: the point where incremental gas injection yields diminishing returns in production.

Required Gas Injection Rate

Qg = qL * (GLR_total - GLR_formation)

Continuous Gas Lift — Pressure Balance

Pr - ΔP_IPR - ΔP_tubing(GLR) = WHP

Worked Example

Given: Well depth = 8,000 ft TVD, Pinj_surface = 1,200 psi, kill fluid = 9.0 ppg, design ΔP = 50 psi per valve, WHP = 200 psi.

Step 1: Kill fluid gradient:

Gradient = 0.052 * 9.0 = 0.468 psi/ft

Step 2: First valve depth:

At depth D1: Pinj_D1 ≈ 1,200 + gradient_gas * D1
Kill fluid pressure = 0.468 * D1
D1 found where: 0.468 * D1 = Pinj - 50
Approx: 0.468 * D1 = 1,200 - 50 = 1,150
D1 = 1,150 / 0.468 = 2,457 ft

Step 3: Second valve depth:

After first valve unloads, producing gradient above V1 is lighter (say 0.35 psi/ft with gas):

P_at_V1 = 0.35 * 2,457 + 200 = 1,060 psi (tubing at V1)
V2 depth from V1: 0.468 * ΔD = Pinj_V1 - 50 - P_at_V1
Continue iteratively...

Typical spacing: 5–8 valves for an 8,000 ft well.

Valid Ranges

Parameter	Typical Range
Injection pressure	800 – 2,500 psi surface
Number of valves	3 – 12
Valve spacing	500 – 2,500 ft between valves
Design ΔP per valve	25 – 100 psi
Operating GLR	300 – 2,000 scf/STB
Max depth	10,000 – 15,000 ft (limited by gas pressure)

References

Brown, K.E. (1980). The Technology of Artificial Lift Methods, Vol. 2a. PennWell.
Winkler, H.W. & Smith, S.S. (1962). "Gas Lift Manual." API.
Takacs, G. (2005). Gas Lift Manual. PennWell.
PetroWiki — Gas lift: https://petrowiki.spe.org/Gas_lift

Gas Lift Valve Spacing