What Wireline Is and Why It Is Used

An oil or gas well is not a simple hole. After drilling, the well is lined with steel casing and completed with a string of production tubing. Oil, gas and water flow up this tubing to the surface. The tubing also holds equipment: valves, landing nipples, gauges and gas lift mandrels.

Over the life of the well, people need to work inside this tubing. They need to measure pressure, open or close a valve, set a plug, remove sand or check the depth of the bottom of the well. This work is called well intervention.

Wireline is the most common way to do it. A wireline unit at surface has a drum of wire or cable. The crew attaches a string of tools to the end of the wire and lowers it into the well. Gravity takes the tools down. The winch pulls them back up. The crew moves the tools up and down to make them work.

Why not kill the well?

To kill a well means to fill it with heavy fluid so that the fluid pressure is higher than the reservoir pressure. The well then cannot flow. Killing a well is sometimes necessary, but it has costs:

• Production stops for a long time, often days.
• Kill fluid can enter the reservoir rock and reduce how well it flows later. This is called formation damage.
• A rig or a hoist may be needed, which costs much more than a wireline unit.

Wireline avoids most of this. The well stays under pressure, the job is often finished in hours, and production can restart soon after. This is the main reason wireline is used so widely.