What is Slickline Operations ?

Slickline Operation

The term Slickline relates to the use of a wire or braided line to convey downhole tools or equipment in a wellbore. The first use of wire in a wellbore was as a measuring device. In the construction of the early wells dug by hand, sticks were used to measure depth. The stick was laid on the ground and the distance/length stepped off. Occasionally, for important measurements a surveyor’s chain would be used. To create a hole in the ground, early drilling operations used a pointed tool on a rope. However, as the work progressed, the rope stretched and often broke. The length of the rope could not then be used as an accurate measure.

To overcome the weakness of rope, wire cable was used. By this time, a method had to be devised to measure the depth of the hole. Normally the hole had water in it to help soften up the dirt, clay sandstone or limestone rock. If the driller used a rope with markings, the rope would be wet as it came out of the hole and would rot while being rolled up on a winch type spool or drum. The drillers started using cable, but it was bulky and as it stretched going in the hole, the weight of the cable either broke it or stretched between the markings on the cable.

Around the same time as the use of rope and cable, some drillers were using a flat steel tape with markings on it. The tape would be lowered into the wellbore, however, it suffered the same problems as the cable and rope, as weight exceeded the strength of the tape cross-section, it would part. The subsequent use of wire offered several advantages. It weighed less than a cable, was easier to handle than a rope and the length or depth to which the wire could be used was be greater. This was accomplished by putting the wire on a drum, which could be lowered and raised by a winding handle. As the wellbores increased in depth, a winding handle with a gear ratio was added to pull up the greater weight. By this time, a brake hand was added to the other side of the drum to control the speed of the line going in the hole. The principal power source at this time was steam and a steam operated engine was used to pull the line out of the hole.

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The first noted use of slickline was by Halliburton to follow a cement plug down while cementing a well. These units were originally mounted on the rig, although they later became part of the equipment of the service engineer and were operated off of the left rear wheel of a car or pickup truck. From this early efforts a unit known as a side-winder was developed – a spool of wire on a drum would slide out on a frame from the bed of a pickup truck. The left rear wheel was jacked up, a sheave, drum or cathead was attached and a rope was run around it to the drum of wire. This was prevalent in the 1940’s.

The operator told the helper how fast to run the engine and winch, the helper being positioned in the cab of the truck with his foot on the gas pedal! There was no weight indicator and the operator had to guess how much he was pulling on the wire by how far he could push down on it. To measure how deep he had gone in the hole, the operator would count the number of layers of wire that had gone in the hole and come up with a figure for depth, determined by the circumference of the drum. This was a crude guess, but an experienced operator would generally be off only 5 to 10 ft if measured by a counter.

From that method came the skid units with belt drives and clutches to improve control of the winch. A counter head and a device to measure the amount of pull (weight) on the wire had been developed by this time. The counter head was developed by Halliburton and the OD of the wire determined the size of the wheel in which the wire ran. To measure the pull on the wire, there were two methods, electric and hydraulic. Much of the same principals are still applied in the design and use of modern slickline equipment. However, with increased wellbore depths and the growing complexity of downhole completion equipment, the applications for slickline have increased significantly. Almost every wellbore will at some time be accessed by slickline. Even highly deviated or horizontal wells can require slickline access for the installation or servicing of upper wellbore components. Slickline (and occasionally braided line) is commonly used in the following operations:

• Checking the production tubing drift

• Checking the build up of wax, scale or wellbore deposits
• Confirming the well depth or clearance to perforations
• Running and pulling plugs or flow control devices
• Opening and closing sliding side-doors or similar completion equipment
• Conducting pressure and temperature surveys using mechanical or electrical gauges and recorders
• Installing tubing pack-offs or similar completion devices
• Logging and perforating

The majority of blowouts and pressure related incidents are caused during well intervention, using equipment and techniques such as slickline, CTU, snubbing or workover rig operations. Efficient, safe slickline operations are essential, but can only be achieved through good planning and implementation of correct procedures. The use of appropriate tools and correctly maintained equipment is an integral part of successful, safe, slickline operations. The necessary skills and operator competency are a result of thorough theoretical education and practical training.