Petroleum engineers have many levers they can pull to try to improve the efficiency of a downhole rod pump. Some of those tactics involve expensive workovers. Some require adjustments to the tool string. However, there is one simple and inexpensive change that can have a significant impact on production and cost containment. Yet it is often overlooked. This article highlights that frequently neglected lever.
Common Challenges with a Downhole Rod Pump
The trifecta of challenges that frequently plague the production of a downhole rod pump are gas, sand and scale. What’s more, each of those issues is often associated with a well’s tubing anchor catcher, or TAC.
- Gas Locking – When a downhole rod pump gas locks, the area in the pump barrel below the plunger contains mainly gas. And gas is compressible, where fluid is not. Therefore, on the downstroke, all that happens within the pump is gas compression and expansion. A primary contributor to gas locking is the small annular area between the well casing and a standard B2 TAC. This small annular space creates a chokepoint that traps gas below it. Eventually, that gas will build up and gas lock the downhole rod pump.
- Sand Bridging – While formation gas is accumulating below the TAC, sand and sediment are building up on top of it. Over time, that sediment plugs the small annular space at the top of the TAC. The result is a stuck anchor – often requiring an expensive fishing job – and an even greater barrier to gas flow.
- Scale Formation – The small annular area around a standard B2 TAC creates a pressure drop as fluid moves across it. That pressure drop contributes to the formation of scale, iron sulfide and paraffin. In turn, those minerals can slow production and limit the effectiveness of a downhole rod pump.
Optimize the Downhole Rod Pump by Changing the TAC
Replacing a standard B2 anchor with a slim-style tubing anchor, such as the Slimline TAC from TechTAC, can mitigate these issues, and in turn, boost the production and lower the lifting costs for wells using a downhole rod pump for artificial lift. The Slimline TAC, for example, features a reduced outside diameter (OD) compared to a standard anchor. That smaller OD provides up to 245% more flow-by area around the tool. Greater flow-by area allows gas to flow up the annulus. It also allows sediment to drop down past the anchor without creating a choke point that restricts flow and leads to the formation of scale, paraffin and other deposits. In other words, by simply switching the kind of TAC used with a downhole rod pump, an operator can mitigate the effects of gas locking, sand bridging and scale formation.
Validated by CFD Analysis
The Slimline TAC’s ability to improve the efficiency of a downhole rod pump by mitigating or even eliminating the effects of gas locking, sand bridging and scale formation has been validated by a recent computational fluid dynamics (CFD) study. The independent consulting firm Imaginationeering provided “a comparison CFD analysis of a gas flow within the annular space around two types of a 5.5-inch tubing anchor catcher to assess the differences between them in terms of flow parameters.” Specifically, the analysis compared a standard B2 TAC and a Slimline TAC. Both anchors were tested in relation to fluid velocity, pressure drop, turbulence, vorticity and other factors.
The analysis found that the net pressure drop around a standard B2 TAC, as fluid/gas passes through the annular cavity around the anchor, is more than double the pressure drop around the Slimline TAC. It also highlighted the Slimline anchor’s noticeable advantage creating a laminar flow. It outperformed the standard B2 anchor in reducing the turbulence and vorticity strengths within the flow field.
In other words, the standard B2 TAC creates a greater pressure drop and increased turbulence. And those factors can have a material impact on downhole rod pump performance. In particular, they are major contributors in the formation of scale and the advent of gas locking.
Customers Use the Slimline TAC to Improve Downhole Rod Pump Performance
Many customers have used the Slimline TAC to improve the efficiency of a downhole rod pump. The following statements highlight several such experiences.
Reducing the Impact of Sand and Scale
“We have one well that had to be pulled every 3 months due to scale. After installing a Slimline TAC, we didn’t need to pull it for 2 years.”
>> Sr. completion foreman with a U.S.-based oil and gas company
“We were having problems getting standard anchors to both set and release due to sand and scale. With the increased annular area the Slimline provides, sand was able to fall past the anchor instead of accumulating on top of it. Both sand and scale bridging issues were dramatically reduced.”
>> Rig operator with a large U.S.-based oil and gas company
Mitigating the Effects of Formation Gas
“[Slimline anchors] work well for gas interference issues in our wells with 5.5-inch casing. We’ve seen a 25- to 30-percent increase in the volume of gas being discharged on the surface.”
>> Production superintendent with an independent E&P company operating in the DJ Basin
“We had one well that had a 500,000 cubic feet of gas increase per day just by switching to a Slimline anchor.”
>> Sr. completion foreman with a U.S.-based oil and gas company
Increasing Production
“Wells do produce higher rates with a Slimline tubing anchor, so we want to run them where we can get them set without backing off tubing.”
>> Engineer with a large U.S.-based energy company
“All three wells [we switched to the Slimline TAC] went from producing roughly 40 barrels per day to approximately 80 barrels per day – a 100 percent increase.”
>> Production superintendent with an independent E&P company operating in the DJ Basin
Minimizing the Risk of Stuck Anchors
“We used to budget every year for 1 in 20 of the tubing anchors we ran to get stuck and need to be cut over. Since switching to the Slimline TAC, our number of stuck anchors has decreased dramatically.”
>> Engineer at a mid-sized production company operating in the Permian
“One of our oilfield customers ran four standard anchors down the same well, and each time the anchor would get stuck and then shear. When they finally tried a Slimline, the anchor set right away and has worked well ever since.”
>> Manager at an oilfield supply company in the Southern United States
Conclusion
Petroleum engineers looking to improve well performance may benefit from using a slim-style TAC. One such product is the Slimline TAC from TechTAC. It has a track record of improving the efficiency and effectiveness of wells that use a downhole rod pump.
According to Bruce Friesen, a petroleum engineer and former global artificial lift advisor for BP, “[There are] multiple benefits of running the TechTAC Slimline anchor. Number one, reduce pressure and temperature drop, reduce turbidity and turbulence, which all four of those things contribute and cause the formation of scale, iron sulfide, paraffin and solids. [Eliminate] all those parameters … then you don’t have plugging. You don’t have stuck anchors. You don’t have fishing jobs. And you also don’t have what is one of the biggest issues and problems and headaches in the oil patch is gas locking of your rod pump.”
To learn more about the Slimline TAC, including technical specifications, sizes and authorized dealers, download the Engineering Info Packet or Request a Quote.
