It doesn’t matter what type of mechanical lift system you use; it will use some sort of pump configurations for transferring the hydrocarbons from the well to the surface. While there are several styles offered, every pump utilizes the same key components.
To differentiate one style from the next, each pump is distinguished by how each pump functions, and how the various components are put together. However, to be a successful operator; a lease pumper should be aware of both the similarities, and the differences, of each mechanical lift pump style.
Downhole Pump Components
Downhole mechanical pump lift systems consist of five key components. These include:
- Barrel Tube
- Holddown Seal Assembly
- Standing Valve
- Traveling Valve
Barrel Tube. The pump portion where the fluid flows from the formation is known as the barrel. Depending upon the pump design, the barrel can either be a section of the tubing, or an entirely separate component the lease pumper will be required to insert into the tubing.
Other than that, the key differences between barrels are:
- type of metal
- metal thickness, and
- the method the barrel houses the plunger
In most cases, you can find pump barrel tubes in one of three thickness sizes: heavy wall, standard wall, and thin wall.
The material used can vary in both the type and grade of the metal; and is typically either: brass, carbon steel, Monel, or stainless steel. Depending upon the manufacturer, it is often common for the metal to be treated in order to help protect it from chemicals and corrosion. This also helps to further harden the metal for additional strength.
Prior to installation, the barrel tubing has to be machined in order to ensure the correct thread design and clearances are utilized for each specific type of plunger. Depending upon the pump, a liner may also be used; in these situations, the barrel design must also accommodate for this extra layering.
Figure 1. Barrel Tube Examples (Harbison Fischer)
Holddown Seal Assembly. The entire purpose of the holddown (or holddown seal assembly) is to create a seal between the tubing and the pump.
Typically, one of three types of holddown assemblies are used: two mechanical options and one cup type (as seen in Figure 2). Each assembly must be accurately installed and utilize the appropriate seating nipple in the tubing string.
Cup-type assemblies generally use one of two seating nipple lengths. The short model provides one seating area, while the longer seating nipple option offers the ability to be reversed, allowing it to turn around in the tubing to create a new seating area during situations where the other area has been damaged. However, while both cup and mechanical style holddowns both offer satisfactory installations; in cases where the bottom hole temperature is 250 degrees Fahrenheit or above, the operator should opt for a mechanical holddown option.
Figure 2. Examples of a Holddown Seal Assembly. The one on the right is a cup option, while the two on the left showcase the mechanical style options. (Trico Industries, Inc.)
Plunger. The purpose of the plunger is to remove the liquid from the pump’s base and to bring it up to the top of the pump. This motion is either due to: the barrel traveling around the plunger, or the plunger traveling within the barrel.
They are categorized in one of two areas: metallic or nonmetallic; with each available in a large array of metal arrangements. Most of these arrangements offer the option for treatment using the similar procedures used on the barrels.
For a successful downhole pump assembly, the space between the metallic plungers and the barrel must be extremely precise. Therefore, these spaces often have to be corrected once the installation in the hole is complete. This is generally due to the system normalizing to the pump temperature and bottom hole temperatures. Both barrels and plungers are created and/or treated to withstand corrosion from both H2S and CO2. The conditions of the well will determine whether to utilize a grooved or non-grooved plunger.
Soft-pack plungers (also known as non-metallic plungers) are available in a variety of cup and ring designs. Ring design options are also known as the: composition ring, regular flexite, soft-packed, wide flexite, or an assortment of additional terms. The softpack cup assembly and composition are typically selected for well conditions with highly abrasive or corrosive fluid properties, high temperature fluids, larger fluid gravity, and/or assemblies with poor lubrication.
Figure 3. Plunger Examples (Harbison Fischer)
Standing Valve. The standing valve located at the base of the pump is a one-way valve that permits the liquid to flow from the formation to the barrel.
As shown in Figure 1, the standing valve consists of a ball that rests on a small-lipped seat; and the ball and seat assembly is contained within a valve cage with a ball located on top (or up) as it is positioned into the well.
Since the pressure from below can cause the ball to unseat, and for the fluid to leak past the valve; this pump option uses the pressure from above the ball to keep it situated in the seat, and to prevent the fluid from flowing back past the valve.
Figure 4. Example showing the components of a ball and seat standing valve. (Harbison Fischer)
The ball and seat are completed and placed together against one another as a set, and then sealed together as a unit. These two components should always be kept together. Each seat size has two sizes of balls available. They are the standard API (American Petroleum Institute) size and a smaller alternative option that permits violent fluids and debris to travel between the ball and valve guides. In some circumstances, double valves are installed in order to resolve specific issue.
Traveling Valve. The traveling valve is located at the pump’s height. Similar to the standing valve, the traveling valve is a one-way valve. This permits the oil to flow out of the barrel, while keeping the fluid from flowing back into it.
Although the traveling valve and standing valve are separate parts for each pump; these two valves can be the same composition and size, allowing them to be interchangeable. As a result, the construction and operation of these valves are the same.
Downhole Pump Designs
There are three types of pumps and one tubing pump (see Figure 5) used in the four basic styles of downhill pumps. These include:
- Insert Pumps
- Stationary Barrel, Bottom Anchor Insert Pumps
- Stationary Barrel, Top Anchor Insert Pumps
- Traveling Barrel, Bottom Anchor Insert Pumps
- Tubing Pumps
Figure 5. Examples of the 4 main pumps used in the majority of downhill pump designs (Trico Industries, Inc.)
Insert Pumps. When working in oil production, the word “insert” specifies the pump has already been constructed as a complete and working pump, and has been placed into the tubing string. Insert pumps can contain either a stationary or moving barrel, and is typically anchored that is typically anchored to either the bottom or top.
Due to this, the three insert pump styles include:
- Stationary Barrel, Bottom Anchor
A stationary barrel, bottom anchor pump can be used in shallow to very deep wells, and is typically the most accepted insert pump option. Due to the design, the traveling valve has the option to be smaller than the standing valve. The fluid column inside the tubing helps to constantly support the pump barrel; with the reduction in differential pressure, the pump has improved efficiency and a longer pump life.
A common disadvantage to this style of insert pump is sand tends to settle around the barrel and the scale can make it difficult to pull the pump. Thankfully, this issue can be resolved by stripping-the well (or stripper job) where the workers simultaneously pull the rods and tubing.
- Stationary Barrel, Top Anchor
This pump style has the holddown located at the top of the pump. It is situated so the pump hangs below both the tubing perforations and the seating nipple. This type of arrangement is great with sandy wells (especially shallow ones with a depth of less than 5,000 feet), due to the fluid’s whirling motion created during operations in the area at the pump’s top.
Inside the barrel pump, the pressure is far higher than the casing pressure located outside of it. Allowing the barrel pump’s inside the ability to resist the pressure created by the fluid column. However, this does limit the depth at which the downhole pump can operate safely; due to gas pounding (a very serious issue known to split the barrel).
- Traveling Barrel, Bottom Anchor
This versatile barrel option will operate in corrosive, normal, and sandy wells with positive results. During each stroke, the barrel rushes the liquid around the bottom of the pump causing the possibility of sand to stick to the pump inside the hole to reduce.
If the design uses an open-style valve cage, it will provide less restriction during the pumping of heavy crude oils; while the traveling barrel option offers a better defense against bursting, especially for designs using a heavy barrel.
One of the disadvantage to this style of pump is it more likely to gas lock than stationary barrel options. The traveling barrel is more likely to experience wear during operations because the traveling barrel is larger than the standing valve. This also makes it less productive in situations with crooked holes; and therefore, the pump may require a guide.
Tubing Pumps. You can differentiate an insert and tubing pump, because the tubing pump is placed down the hole as a portion of the tubing string, with the standing and traveling valves typically running on the rod string. Once the standing valve has dropped to the hole’s base, the rods turn and discharge it. Then once the rods are repositioned a few inches higher, the pump is prepared to pump again. Standing valves can be attached (and re-attached) for re-running, pulling, and servicing rods.
As you can see in Figure 5, the up-arrow indicates both where the clutch is located and where the pump splits, allowing it to pump. The portion above the up-arrow is commonly referred to as the action section. This section moves along with each pump stroke (going up and down), and also contains both the plunger and traveling valve. While the section below the up-arrow indicates the stationary section of the pump containing the standing valve.
One of the clear advantages of using a tubing pump is the ability to pump larger volumes in water flood plans. However, there are plenty on the flip side. For instance, a big disadvantage is the necessity for removing the tubing string for pump barrel maintenance and service.
Another big tubing pump disadvantage is the rod string’s high fluid load; as the weight from this load can stretch the rod resulting in a bottom hole stroke loss.
Other Pump Types. Like other devices, there are a wide variety of downhole pump designs. While some are variations of the previously described options; others are more unique, and are created to meet the specific requirements of an installation. Therefore, pump manufacturer assistance is indispensable when planning your pump installation design, especially for wells with special requirements.
Is your appetite for oil & gas operating knowledge insatiable like ours? 😀 If so, check out these related articles, A Pumper’s Basic Guide to Mechanical Lifts in Oil & Gas Production, A Basic Guide to Operating and Servicing Pumping Units in Oil & Gas Production and, A Basic Guide to a Standard Wellhead Design and the Polished Rod in Oil & Gas Production – they’ll be sure to pump you up!!!