Workover/Intervention Operations

Who have worked with me, knows I'm a not a great specialist in Workover operations, but I'm a great curious about all offshore operations aspects, i received a request for a magazine for say anything about Workover... i hope you all enjoy the read.

Currently there are more than 3,000 subsea wells scattered across the globe, with more being drilled every day. Many of those wells are already a decade old with many more not far behind. That’s why in the last several years the techniques offered through well intervention have become ever more necessary to keep up with rising global demand for oil and gas.\

Well intervention holds the potential to extend the productive life of aging wells and repair damaged or underperforming wells. Well intervention can bring oil and gas companies substantially higher profits off otherwise non-economical wells.

But what exactly is well intervention?

Generally speaking, well intervention is any process that enhances the quality of the subsea well, provides data to help manage the production rate of the well or shuts off and safely abandons a flowing well. One of the biggest challenges in subsea well intervention is keeping costs down. So rigorous and extensive preplanning is used to identify the best potential solutions while mitigating a multitude of known and unknown risks.

After assessing a particular well’s condition and selecting a proper treatment, which could involve a number of different procedures and contingency plans, a specific type of vessel is then selected to carry out the task. Most operations can be carried out using light and medium intervention vessels equipped with dynamic positioning, but for heavy intervention work, like redrilling an under-producing well, an offshore drilling unit is needed.

Methods

Among all the various types of well intervention operations, through tubing is the most commonly applied. Through-tubing enables recompletion, stimulation or repair work to be done inside a flowing oil or gas production line for the entire length of the well.

This procedure is used to complete many different tasks including the removal of obstructions inside the well that may be blocking the flow of hydrocarbons, simply evaluating the well’s condition, stimulating the well chemically or repairing a damaged well casing. Each job requires a specific type of tool that can be delivered down inside the well itself and in light intervention procedures the systems used include coiled tubing, electric line (e-line), slickline and braided wireline.

Slickline is an unbraided wire used to deliver a wide array of specialized tools down into the well for maintenance and data collection. E-lines provide more flexibility for mechanical and electrical operations and can also send back real time logging data which means engineers don’t have to wait for the tool to be pulled back out of the well to learn of its condition.

E-lines can include the use of a braided line which is more complex than slickline and requires a special grease injection system to ensure there is enough pressure for the blowout preventer to seal around the wire as it goes down into the well.

Braided lines are stronger that slicklines and can be used to perforate wellbores with explosive charges or fish out logging and monitoring tools placed deep inside the well. Both slickline and e-line jobs can be completed without the use of a rigid riser that connects the subsea well head to a vessel floating on the surface.

Coiled tubing is by far the most effective and versatile tool for well intervention. Coiled tubing is a continuous string of tubing that can be rolled onto a spool and is used is often used to pump chemicals or gasses directly into the well to relieve blockage and increase flow. But coiled tubing is used for a wide variety of other tasks such as drilling, logging, cleaning, cementing,” fishing” out tools and well completion and production. In many cases coiled tubing requires a riser or a subsea tool known as an injector head that is placed on top of the well and can cut through the coil to shut off the flow of oil or gas if an unexpected problem arises to perform these types of operations offshore.

Elon Chaves - Senior Subsea Engineer