Gas Lift Tech Lecture 2 Slides, Slides of Engineering

Download Gas Lift Tech Lecture 2 Slides and more Slides Engineering in PDF only on Docsity!

• GAS LIFT - CLASS #

Valve Mechanics

• Gas lift valves are constructed where all components must be fitted into a small cylindrical shaped tube. A typical valve must have a closing force, an opening force, and a flow regulating orifice.
• If tubing pressure causes gas flow regulation, it is referred to as a tubing or fluid operated valve (or “automatic valve”).
• If casing pressure causes gas flow regulation, it is referred to as a casing or gas operated valve (or as “human operated”).

Mandrel & Gas Lift Valve

Packer Gas Lift Mandrel Production string Perforations

Casing and Tubing Valves Casing operated valve (“human operated valve”) Tubing operated valve (“automatic valve”)

Valve Mechanics

• Gas lift valves operate in accordance with certain basic principles, and are mostly compared with pressure regulators. The component parts are: 1. Body 2. Loading Element - Spring, gas, or combination of both 3. Responsive Element - Metal bellows, piston, or rubber diaphragm 4. Transmission Element - Metal rod or rubber diaphragm 5. Metering Element - Orifice or port

Casing operated valve:

• A regulator responding to upstream pressure.
• A control valve at the surface operates the downhole valve.
• Pinching down on manual valve at surface reduces casing pressure, which pinches down on the gas lift valve, thereby reducing gas flow.
• Opening the surface valve increases casing pressure, causing the gas lift valve to open and increases the gas flow thru the valve.

Advantages & Disadvantages

Casing operated:

* pumper has surface control

* can only gas lift one tubing string

* inefficient – pressure drops to unload are lost energy

Tubing Operated:

* multiple tubing strings gas lifting from one annular

gas column

* automatic – requires minimal pumper intervention

Opening Pressure of Valve Under Operating Conditions

• The force balance for valves (figure 5) which are closed, but on the

verge to opening will be: F

c

= F

o F c is the force in pounds holding the valve closed and Fo is the force in pounds trying to open the valve.

• Setting these expressions equal, dividing by A b , and solving for P o , [pressure to open] = [bellows effect] + [spring effect] – [tubing effect]

Tubing Effect (T.E.) For example, if there is a pressure in the tubing opposite the flow valve of 300 psig and the ratio A v /A b is 0.11, the Tubing effect (T.E.) is: 𝑇. 𝐸. = 300.

1. 11 1 − 0. 11 = 37 𝑝𝑠𝑖𝑔 Or the opening pressure P o is reduced by 37 psig

Opening Pressure in Valve Tester

• In a valve tester, the tubing pressure opposite the valve is zero (p t = 0). With a force balance, opening and closing forces are equated,

Closing Pressure of valve under operating conditions

• The valve is now open and ready to close, and the casing pressure is operating over the total effective bellow area (figure 6.11c). The force balance is:

Tubing operated valve:

Fully opened – pressure on stem bottom = P t Fully closed – pressure on stem bottom = P csg   c bT b t b v F  P A  S A  A o tc b v o v F  P (A A ) P A

𝑡𝑐

𝑡

𝑏𝑇

𝑣

𝑏

𝑜

𝑣

𝑏

𝑣

𝑏 At Fully Closed Position:

Belows Pressure at Operating Conditions