Snubbing

Snubbing is technique to install or remove tubular from a well, while the well remains pressurized (live well). This technique is used when it is not possible or not desired to kill a well (dead well). Killing a well means depressurize the well by pumping a heavy fluid or mud inside the well. The advantage of Snubbing is that work can be performed without killing the well thus eliminating reservoir formation impairment or costly stimulation operations. Before starting a snubbing operation, dedicated engineering is required; the operation and contingencies must be in place to ensure that operations on live wells can be performed safely.

HWO/Snubbing unit

Snubbing operations require the use of a hydraulic workover unit (HWO).  The HWO/Snubbing unit is designed to deal with the technical challenges present during work on pressurized wells. Typical chanllenges are buckling of tubular, push and pull forces and lubrication of tubular in- and out of the pressurized well.

HWO/Snubbing units have a small footprint, are flexible and are easy to mobilize. These properties make these units very suitable to work  offshore and onshore allowing tailored solutions for each well.  

Function and use

Traditional Snubbing has been developed as a technique to regain control over pressurized wells which were difficult to kill with conventional methods. Today, the advantages of Snubbing has made it a widely used well intervention technique which can be used for;

• •  Underbalance Sand screen deployment
• •  Underbalance Packer milling / completions removal 
• •  Installation of velocity strings
• •  Underbalance casing drilling in unstable formations
• •  Installation and removal of tubular out of gas storage caverns
• •  Installation of kill strings / well control
• •  Underbalance well cleaning / deepening
• •  Setting of (bridge) plugs, packers and isolation valves
• •  Underbalance fishing

3 Stages during Snubbing

Characteristic for Snubbing is the stage where the weight of the tubular is less then the upward acting forces caused by well pressure and buoyancy. This so called "pipe light" stage introduces a number technical challenges like buckling of tubular and push forces instead of pull forces. Once the weight of the tubular equals the upward acting force created by the well pressure and buoyancy, the balance point has been reached. "Pipe heavy" refers to the stage where the weight of the tubular is larger then the upward acting forces. During the entire Snubbing operation well pressure shall be controlled and sufficent barriers shall be in place to avoid uncontrolled pressure release.