澳洲大学石油工程讲座2.3 continuous flow gas lift rev feb 200

Figure 1

Similarities to flowing well Surface pressure and flow rates constant after stabilized flow reached Flowing bottom-hole pressure constant for constant gas injection rate Production rate depends on constant flowing bottom-hole pressure being below the reservoir pressure3

Differences Pressure gradient in tubing changes significantly below point of gas injection (working valve), Fig. 2 Gas-liquid ratio can be changed by operator Point of gas injection can be changed (within limits)4

Figure 2

Types of wells suited for continuous flow gas-lift

High producing capacity, high formation pressure wells

Types of wells suited for continuous flow gas-liftIf producing capacity too low, well should be placed on intermittent gas-lift

Types of wells suited for continuous flow gas-liftFormation pressure must be great enough to work against pressure in tubing due to injected gas Minimum gradient for continuous flow = .100 to .150 psi/ft. Pressure gradient cannot be lowered by gas injection to TD of completion interval

Types of wells suited for continuous flow gas-lift

Gradient below working valve as high as 0.45 psi/ft. For overall average gradient of .150 psi/ft, pressure drop in tubing is 1,500 psi for 10,000 ft. well

Types of wells suited for continuous flow gas-lift Wells producing sandFlowing bottom-hole pressure remains constant

Sand may cut out other artificial lift equipment Slim hole completions

Types of Installations Open (Figure 3)Tubing hangs free in casing, no packer or standing valve Annulus fills with liquid when well shut-in Liquid may cut out lower gas lift valves if unloaded often Should not be used unless packer not viable11

Figure 3: Open

Types of Installations Semi-closed (Figure 4) Tubing and packer, no standing valve Liquid cannot enter annulus after initial unloading

Types of Installations Semi-closed (Figure 4)Check valves prevent flow from tubing to annulus Liquid level remains at/below lowest operating valve Recommended installation for most continuous flow gas-lift14

Figure 4: Semi-Closed

Types of Installations Closed Adds standing value to semiclosed arrangement Principle of operation for continuous gas-lift (Fig. #2) Gas injected continuously at one location in tubing after well unloaded16