There are a number of problems that can develop in a producing well that can negatively affect operations, production and ultimately revenue generated, such as failure of mechanical equipment, changes in production characteristics, plugging and increases in injection pressure. After a well goes into production, these events may occur, requiring modification of the well in order to achieve optimal production; this is called well intervention.
Many times, at the slightest hint that there may be a problem with a producing well, well intervention solutions are sought. Should these problems be overlooked, the well may reach zero production over time. The problem within the well and the economics of the proposed solution are weighed in deciding how to solve the production problem.
Many times, remedial work constitutes employing a workover rig to repair the well. Similar to a drilling rig, a workover rig is smaller and requires no mud pumping or pressure-control systems. A workover rig is used to retrieve the sucker rod string, pump or production tubing from the well or run wireline cleaning and repair equipment into the well. It is important to note that with workover activities, production must be stopped and the pressure in the reservoir contained, a process known as “killing” the well.
A cost- and time-effective solution for well intervention operations employs coiled tubing. Instead of removing the tubing from the well, which is how workover rigs fix the problem, coiled tubing is inserted into the tubing against the pressure of the well and during production.
The coiled tubing is a continuous length of steel or composite tubing that is flexible enough to be wound on a large reel for transportation. The coiled tubing unit is composed of a reel with the coiled tubing, an injector, control console, power supply and well-control stack. The coiled tubing is injected into the existing production string, unwound from the reel and inserted into the well.
Coiled tubing is chosen over conventional straight tubing because conventional tubing has to be screwed together. Additionally, coiled tubing does not require a workover rig. Because coiled tubing is inserted into the well while production is ongoing, it is also a cost-effective choice and can be used on high-pressure wells.
Coiled Tubing Operations
All performed on a live well, there are a number of well intervention operations that can be achieved via coiled tubing. These include cleanout and perforating the wellbore, as well as retrieving and replacing damaged equipment.
Additionally, some advances in coiled tubing allow for real-time downhole measurements that can be used in logging operations and wellbore treatments. Enhanced Oil Recovery (EOR) processes, such as hydraulic and acid fracturing, can also be performed using coiled tubing. Furthermore, sand control and cementing operations can be performed via coiled tubing.