Magazine - May 2009

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Artificial Lift

Production wells are free flowing. When a well pressure has declined to the point at which the well no longer produces by its natural pressure. Some artificial methods are: (Beam pump, Electrical Submerged pump and Gas lift)


Beam Pumps

Also called as Donkey Pumps ,are most common artificial lift system used in land based. A motor drives a reciprocating beam, connected to a polished rod passing into the tubing via a stuffing box. The sucker rod continues down to the oil level and is connected to a plunger with a valve.

On each upward stroke, the plunger lifts a volume of oil up and through the wellhead discharge. On the downward stroke it sinks (it should sink, not be pushed) with oil flowing though the valve.

Advantages:

1. Can be used for wide range production capabilities
2. Can produce most wells to depletion at limited rates and depths
3. Highly reliable and relatively easy to analyse by using several different means
4. Corrosion and scale problems easily treated
5. Can produce high temperature or viscous oil
6. Low cost production operation

Disadvantages:

1. Installation not suitable for crooked hole work
2. Depth and volume limited by rod weight and strength
3. High gas-oil ratio wells as well as sand and paraffin content in production fluids
4. Weight and size can prohibit use in offshore installations
   

Electrical Submerged Pumps (ESPs)

A motor driven centrifugal pump with rotating blades on a shaft on the bottom of tubing.


Advantages:

1. Can be operated in deviated or directionally drilled wells although recommended operating position is in straight section of well
2. Can be operated in deep wells with small casings
3. Very efficient and economical

Disadvantages:

1. Narrow producing range
2. Large volumes of gas can be destructive to the pump
3. Run life adversely impacted by poor quality electric power supply

Gas Lift

High pressure gas is injected into the production fluids within the tubing string. Leads to decrease in the weight of the fluid column and permits the well to flow.

When the gas lift is started up, several gas lift valves must operate in sequence. During the unloading process, the fluid in the annulus between the tubing and the casing is displaced, along with the high pressure injection gas, through the top gas lift valve into the tubing bore.

Advantages:

1. Simple to operate
2. Equipment used is relatively inexpensive
3. Flexible
4. Both high volumes and low volumes can be produced
5. Effective handling of corrosion and high gas-oil ratio production
6. Low operating costs
7. Lower failure rate

Disadvantages:

1. Source of high pressure gas must be available
2. Not cost effective when used for one-well lease or small fields
3. Not very effective for producing deep wells where there is high drawdowns or low bottomhole pressures
4. Accurate gas measurements are not easily obtained
5. Surging flow can be a source of operating problems with surface equipment