Chemical injection pumps for oilfield
Chemical injection pumps are used in the oilfield to deliver specialty chemicals into the production system at specified rates. Reliably and accurately getting the chemicals into the well, the production system, or the pipeline is an important part of any chemical treating program. No matter how great your product is, if it’s not getting where it needs to be, it cannot be effective. Field operators must be familiar with the types of pumps used to apply your treatment chemicals and how they operate. Something as simple as a minor adjustment could mean the difference between a failure and success.
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Why are chemical pumps necessary?
Many treatment programs require that a predetermined concentration, or dosage, of chemical be added to the system on a continuous basis. This requirement calls for equipment that is capable of metering a precise volume of chemical into a system at a rate that will maintain the proper chemical-to-fluid ratio.
Pump types
There are many types of chemical injection pumps used in the oilfield. Some are mechanically operated, such as those driven by direct linkage from the walking beam of a pumping unit. Others may be driven by compressed field gas, air, or by an electric motor.
How do pumps get the right amount of chemical in the system?
Most pumps use either a positive displacement piston (plunger), or a diaphragm to meter the dosage of chemical. The volume of chemical is controlled by adjusting the length of the plunger or diaphragm stroke, the number of strokes per minute, and the diameter of the plunger. Some pumps may even be equipped with dual heads to enable them to pump two chemicals simultaneously.
Is one particular type used more than others?
Positive displacement pumps are used to a much larger extent than diaphragm pumps. The plunger in positive displacement pumps is connected to, and operated by, a ratchet mechanism powered by an electric motor, gas or air pressure, or by mechanical force.
What determines which type of pump is used?
The location in the field, the power that’s available, and the required injection pressures normally dictate the type of pump required. For example, beam operated pumps are normally used where small volumes of chemical are required and where electricity or gas/air is not available.
Gas operated positive displacement diaphragm pumps can be found on flowing wells, pipeline, and in some plant sites. The pumps are designed to operate at higher pressures and output levels than beam operated pumps. Dual head pumps are used quite extensively in plant treating.
Electric pumps are used where there’s no danger of contact with explosive vapors. In settings where there may be intimate contact with explosive vapors the electric motors are housed in explosion-proof housings.
Electrical operated diaphragm pumps are normally used where large volumes of chemical are to be pumped into low pressure systems such as a cooling tower or water holding tank. They are not as common in production treating operations, but this is changing daily.
With the exception of electric diaphragm pumps, these pumps can be equipped with a self-contained reservoir for storing treating chemicals, or they can be connected directly to the drum or bulk storage tank.
Trouble shooting
In case of pump malfunction, you should find out what can cause them to stop working properly and how to repair some of the simple malfunctions. The chemical injection pump is probably the most neglected piece of equipment on the lease, even though the pumper works with it daily. In many cases it is left up to the field engineer to discover and correct the problem.
No matter who is responsible for maintaining these pumps, chemical treatment program will be affected if it stops working in the middle of the night and the chemical doesn’t get in the system to do its job, which most often translates to production problems.
What are some things that can go wrong with these pumps?
Chemical injection pumps can and do appear to malfunction for no apparent reason. When troubleshooting a pump, consider the following possibilities for it not working:
- Does the chemical tank have any chemical in it?
- Is the pump getting power?
- Is there water trapped in gas/air regulator?
- Is the chemical strainer plugged?
- Is the pump air locked?
- Are check valves and seats dirty or worn?
- Is the ratchet mechanism broken or missing a pin?
- Is the setting for metering of chemical accurate?
In some cases a problem might persist even though the pump functions normally and it appears that the proper amount of chemical is being injected into the system. When this happens, check to see if the line between the pump and the injection site is plugged or has a hole in it, which would allow only a portion of the chemical to enter the system.
It's also possible that the pump may be positioned too far from the treating vessel. If this is the case, the chemical may be performing as required in the flowline, but when it gets into the turbulence in the vessel it creates an emulsion.
Having the pump located too close to the treating vessel could be a problem too because the chemical may not have adequate mixing time before entering the vessel.
How do I know the volume and injection rate of the chemical being pumped into the system?
Many chemical drums are equipped with sight glass gauges. These instruments allow you to visually check the level of fluid remaining in the drum. Sight glass gauges allow you to determine the rate at which chemical is used. By closing the tank outlet valve, chemical is pumped only from the sight glass (i.e., "a drawdown" flow measurement), where you can use the graduated markings on the glass to measure the amount per hour being pumped into the system.
The drawdown process has even been automated. Other metering systems such as gear meters and turbine meters have been attempted with limited success, because of fouling and changing viscosity with temperature. Remote monitoring of tank level and drawdown flow rate, along with remote pump control greatly reduce the labor involved with maintaining chemical pumps, reduce over-injection safety margins, and help manage inventory refills.
