About downhole sucker-rod pumps

Pump components

There are seven major components for downhole rod pumps: standing and traveling valves, plunger, barrel, seating assembly, pull tube or valve rod (for insert pump), and the fittings that hold the assembled pump together. The most common of these components and the final types of assembled pumps are covered by American Petroleum Institute (API) Specification 11AX.

Types of pumps

API recognizes two main types of pumps: rod and tubing. Rod pumps also are called insert pumps because they are run (inserted) in the production tubing. Tubing pumps are so named because the working barrel of this pump is coupled with the production-tubing string.

There is a wide range of plunger (or pump-bore) sizes standardized by the industry. The API pump-bore sizes that are currently available range from 1 1/16 to 3 3/4 in. in diameter. This 1 1/16-in. size has been added back in the latest edition of the standard. Additionally, a new barrel type has been accepted in the latest API Spec. 11AX. This is the "X-type" barrel. It has a thin-walled barrel configuration for threads on either end of the heavy-walled barrel and is available for metal plungers only. This type of pump does not require the extension couplings normally needed for heavy-walled barrel pumps. Thus, this pump reduces the burst or collapse concerns of the thin-walled extension couplings and allows deeper producing depths to be attained.

API pumps and nomenclature

While there are only two main types of pumps standardized by API, there are four different types of rod pumps. These are classified by the type of barrel (standing or traveling) and where the pump is anchored (top or bottom). API Spec. 11AX. shows the letter designations for the various types of rod and tubing pumps that are available for different barrel thicknesses and either metal or soft-packed plungers.

The complete pump designation of an API pump adds dimensional diameters and lengths to the letter designations. This has been modified in the latest revision to incorporate all approved sizes and barrel types along with separating the extensions into the top and bottom lengths, if required. The complete API designation includes the following:

• Nominal tubing size (from 1.9- to 4.5-in. OD) - represented with 2 digits
• Basic bore diameter (from 1.0625 to 3.75 in.) - represented with 3 digits
• Type of pump (rod or tubing) - R or T to indicate type
• Type of barrel (heavy, thin, or X type) - single alpha character to represent the barrel type
• Seating-assembly location (top or bottom) - A (for top), B (for bottom), or T (for bottom, traveling barel)
• Type of seating assembly (cup or mechanical) - C or M to indicate type
• Barrel length (ft) - single digit length
• Nominal plunger length (ft.) - single digit length
• Length (in.) of upper extension (if required)- single digit length
• Length (in.) of lower extension (if required)- single digit length

API Spec. 11AX. shows that, for example, a 1¼-in. bore-rod-type pump with a 10-ft heavy-walled barrel, a 2-ft upper extension, a 2-ft lower extension, a 4-ft plunger, and a bottom-cup-type seating assembly that will be used in 2 3/8-in. tubing would be designated as 20-125-RHBC-10-4-2-2.

It is important to know that the users of API pumps need to provide, along with the pump nomenclature, the following ordering information: barrel and plunger material, plunger clearance (or fit tolerance), and valve (ball and seat) and fittings material. The materials normally available for each of these components also are now included in the latest edition of API Spec. 11AX.

Non-API and Specialty pumps

The types of pumps, sizes, and component materials that are included in the API standards are based on the best industry practices that meet widespread industry needs. While API standardizes the majority of pumps and components that are used in sucker-rod lift, there are special parts and pumps that have been developed by manufacturers to try to solve specific pumping problems. This specialty equipment should be considered when best industry practices and standardized components have proved unacceptable. However, the manufacturer of these components should create all parts to the same quality level required in API Spec. 11AX. Useful specialty pumps include the following:

• Casing pump for production without tubing
• Pumps with two plungers that act in series to increase displacement
• High-compression plunger assembly or pump for handling gas-interference problems
• Three-tube pump for handling fines or solids
• Pumps with a shorter barrel than normally recommended, so that the plunger completely wipes solids free of the barrel and prevents sticking.

Additionally, there are special pump components, such as valve rods, valves, and tubing drains, that are sometimes beneficial in situations in which the capabilities of normal API pumps and components have been exceeded. The manufacturer of special, non-API pumps and components should be contacted to determine the working capabilities and limitations of any of these specialty components. However, these items should be selected with care and used only after the best production effort has been thoroughly tested with standard components.