Tubing anchors bring stability and efficiency to wells that use rod pumps. Depending on the unique requirements of each well, different types of tubing anchors may be preferred. Mechanical anchors have been the industry standard for decades. More recently, however, hydraulic tubing anchors have proven to be very effective in certain well designs. This article will outline use cases and considerations for each type of tool.
How Does a Hydraulic Tubing Anchor Work?
This tool uses the pressure within the well tubing to set the anchor. While the hydraulic anchor usually features three slips, like most mechanical anchors, only one of them actuates to set and release the tool. This movable slip acts like a piston to engage all three slips to bite the well casing. When the fluid pressure inside the tubing exceeds the fluid pressure outside the tubing – usually by at least 10 psi – the slip moves into place and sets the anchor. With this tool there are no stretch calculations, because it’s designed to slide down the well even when the slips are engaged, but not up it. That means it can hold the tubing secure near the farthest point of downward stretch on the tubing.
When Does a Hydraulic Anchor Make Sense?
There are two use cases where a hydraulic anchor is ideal:
- Capillary tubing string. In wells where the perforations need additional stimulation or harsh downhole chemicals need to be counteracted, capillary tubing string, or cap string, is an ideal solution. This small, stainless-steel tubing bands to the production tubing to follow it downhole and deliver the necessary chemicals. Using cap string in concert with a mechanical anchor can be very difficult. The sting must be “pre-wound” to account for the surface rotations required to set the anchor. With a hydraulic anchor no surface rotations are needed. The cap string can go straight down the well along with the production tubing. However, it should be noted that a quick-setting mechanical anchor, like the Slimline® QuickSet™ TAC, can be a viable alternative for anchoring tubing with cap string.
- Extreme deviations. Some wells feature deviations that are so extreme it’s impossible to get surface rotation torque down to a mechanical anchor to fully set it. Once again, the hydraulic anchor does not have the same limitation because no surface rotations are required.
How Does a Mechanical Tubing Anchor Work?
This tool typically features three actuating slips that are engaged when a requisite number of surface rotations are completed. Rotating the production tubing sends torque down to the anchor, moving the slips into place to bite the casing. The number of surface rotations required depends on the type of mechanical anchor. For example, TechTAC’s Slimline® TAC and many standard B2 anchor models require 6-8 rotations to fully set the tool. However, a quick-setting anchor like the Slimline® QuickSet™ TAC requires just 1-3 rotations to be fully set.
When Does a Mechanical Anchor Make Sense?
There are several use cases where a mechanical tubing anchor is ideal:
- When a “catcher” is required. The hydraulic tubing anchor is designed to slide down the well casing when it is engaged. Therefore, if the well tubing parts, the parted section will simply fall down the well. The result would be an expensive fishing job. Mechanical anchors like the Slimline® TAC secure the tubing upward and downward. That means parted tubing would simply stay in place awaiting repair.
- Well repairs that don’t require replacing the anchor. Many well repairs do not require the replacement of the production tubing and anchor. If just a sucker rod, pump or surface equipment need to be replaced, the entire production string may not need to be pulled. However, with a hydraulic anchor, once the hydrostatic pressure is released, that anchor disengages. In contrast, a mechanical anchor would keep the production string in tension while the repairs are made.
- Where cost is a key consideration. Depending on the model, a hydraulic anchor can cost 2-3 times more than a comparable mechanical anchor. In some use cases, that higher cost is well worth it; but in others, it’s prohibitive.
- Where precise placement is critical. Setting a mechanical anchor in the optimal position requires precise tubing stretch calculations. A hydraulic anchor does not require a stretch calculation. While that simplicity is an advantage in some instances, it also means the placement of the anchor is somewhat subjective. A mechanical anchor allows engineers and rig crews to place the TAC in a precise location.
Conclusion
Both mechanical and hydraulic tubing anchors have a place in certain well designs. Which anchor is right for your wells depends on several factors, ranging from fluid composition to cost. In many instances, a mechanical anchor like the Slimline® TAC is ideal. In addition to the use cases noted above, the Slimline® features a reduced OD and tapered design that provides up to 245% more flow-by area when compared to a standard B2 anchor. That increased flow area often results in fewer stuck anchors, less gas locking in rod pumps and reduced cutover time. To learn more about the Slimline® TAC and TechTAC’s complete line of tubing anchor solutions, contact the TechTAC® team today!
