Dosing Pump
A dosing pump (also called a metering pump or chemical injection pump) is a low-volume, positive-displacement pump with a precisely controllable and repeatable discharge rate used to inject chemical additives at accurately metered concentrations into drilling mud systems, production flow streams, wellbore fluids, process pipelines, or injection lines, where the accurate delivery of small volumes of concentrated chemicals (corrosion inhibitors, scale inhibitors, biocides, hydrate inhibitors, demulsifiers, H2S scavengers, drag reducers, or mud additives) at concentrations of tens to thousands of parts per million is required to achieve the desired treatment effect without overdose (which wastes chemical and may cause adverse interactions) or underdose (which fails to provide the protection required); dosing pumps are distinct from high-volume process pumps by their ability to deliver very small flow rates (typically 0.001 to 100 liters per hour) with high accuracy (flow rate accuracy of plus or minus 1 to 3 percent of the setpoint) against the full operating pressure of the downstream system (which may range from a few bar in atmospheric mud tanks to several hundred bar in high-pressure pipeline injection applications), achieved through the slow reciprocating stroke of a plunger or diaphragm positive-displacement mechanism that delivers a controlled volume of liquid per stroke (the stroke volume) at an adjustable stroke frequency (strokes per minute) and adjustable stroke length that together determine the discharge rate independent of the suction or discharge pressure.
Key Takeaways
- Dosing pump mechanisms include diaphragm pumps (where a flexible membrane separates the chemical being pumped from the mechanical drive components, preventing any contact between the chemical and the drive oil or mechanical system), plunger pumps (where a precision-ground plunger reciprocates in a cylinder with tight-tolerance seals, delivering high-pressure injection against wellbore or pipeline pressures of 100 to 700 bar), and peristaltic pumps (where a rotating roller compresses a flexible tube to move fluid, used for very low-pressure low-rate applications such as laboratory dosing and surface chemical injection at atmospheric discharge pressure); diaphragm dosing pumps are the preferred design for oilfield chemical injection because they provide zero-leakage injection of hazardous, toxic, or corrosive chemicals (H2S scavengers containing amines, corrosion inhibitors containing quaternary ammonium compounds, scale inhibitors with chelating agents) without any possibility of shaft seal leakage to atmosphere, and they handle chemicals containing suspended solids or crystalline scale inhibitors that would damage the precision seals of a plunger pump; plunger dosing pumps provide higher pressure capability than diaphragm pumps for the same flow rate and are preferred for subsea chemical injection (where injection pressures must overcome the wellbore or flowline pressure plus the hydrostatic head of the injection line from the topside to the subsea injection point).
- Flow rate control in modern dosing pumps uses electronic variable-speed drives (VSDs) or stroke length/frequency adjustment to maintain the target treat rate as production flow rates change: for a corrosion inhibitor injected at 50 ppm by volume in the produced water phase, the required inhibitor injection rate changes in direct proportion to the produced water flow rate (which varies over the well's producing life from low water cut early production to high water cut late production), requiring either manual adjustment of the pump setpoint as conditions change or automatic control of the pump speed/stroke from the flow measurement signal; distributed control system (DCS) integration allows the dosing pump setpoint to be calculated automatically from the production rate signal, water cut measurement, and target treat rate, maintaining the correct ppm concentration continuously without operator intervention; pump stroke counters (which count each pump stroke and accumulate total strokes for totalizing the cumulative volume injected) are used for chemical audit and inventory management, confirming that the calculated total volume of chemical injected over a production period matches the actual consumption observed from tank level decreases.
- Pressure-relief valves and back-pressure regulators are essential safety components in dosing pump systems: a pressure-relief valve set above the maximum allowable working pressure of the injection line protects the pump, injection line, and chemical storage vessel from overpressure if a downstream block valve is inadvertently closed while the pump continues to operate; back-pressure regulators (installed at the injection point where the chemical enters the production line) maintain a minimum downstream pressure that prevents the production line pressure from fluctuating and causing siphoning (reverse flow of production fluid back up the injection line into the chemical tank) when the pump is not stroking; injection check valves (installed immediately at the injection point in the production line) prevent any reverse flow of production fluid into the chemical injection system, which could contaminate the chemical tank, plug the injection tubing with scale or wax, or create a backflow safety hazard if the chemical injection line is open for maintenance; the combination of pressure relief, back-pressure regulation, and injection check valves provides a safe and reliable chemical injection system that protects both the process equipment and the chemical supply system from the various failure modes that can occur during normal production operations.
- Chemical injection rate calibration (stroking the pump to verify actual delivery against the setpoint) is performed at installation and at routine intervals (typically monthly or quarterly) to confirm that the pump is delivering the programmed volume accurately and that diaphragm wear, plunger seal wear, or chemical viscosity changes have not altered the effective stroke volume; calibration is performed by collecting the pump discharge in a graduated cylinder for a measured number of strokes (typically 100 to 200 strokes) at the operating speed and pressure, then comparing the collected volume to the expected volume (number of strokes x programmed stroke volume); API RP 14C provides guidance on chemical injection system design, installation, and testing for oil and gas production facilities, including the minimum calibration frequency and acceptance criteria for dosing pump systems; field calibration differs from bench calibration (performed at atmospheric pressure on clean water) because the actual chemical viscosity and the actual injection pressure affect the delivered volume per stroke for diaphragm pumps (the diaphragm spring preload and the chemical viscosity alter the effective stroke volume); calibration at actual operating conditions (production line pressure, actual chemical temperature and viscosity) is more accurate than atmospheric bench calibration for high-viscosity chemicals or high-pressure injection systems.
- Solar and battery-powered dosing pump systems enable chemical injection at remote well sites without grid power: small-volume piston or diaphragm dosing pumps with solar panel arrays and battery banks provide continuous chemical injection at remote oil and gas production sites (pipeline pump stations, satellite gathering facilities, pad wells in remote locations) where running grid power would be cost-prohibitive; solar-powered dosing pumps typically operate at very low power consumption (1 to 10 watts for the pump motor plus control electronics) and are designed to run at reduced injection rates during low-solar periods (cloudy days, winter low-light) and at programmed injection rates during full sun hours, with battery backup providing injection continuity through nighttime periods; the control logic for solar-powered pumps may include proportional injection (adjusting the injection rate in proportion to the available solar power) or fixed-rate injection with battery power available for full-rate injection regardless of sun conditions (requiring larger battery banks); regulatory requirements in some jurisdictions mandate that corrosion inhibitor injection must be maintained at or above the minimum treat rate at all times (not just during full-sun hours), requiring battery backup capacity sufficient for continuous injection through multiple consecutive overcast days.
Fast Facts
Dosing pumps in the oilfield are manufactured by specialized pump companies including Milton Roy (now part of IDEX Corporation), Prominent, Grundfos, and Seko, as well as by oilfield-specific manufacturers such as Persta (now Halliburton Production Enhancement) and BJ Services (now Baker Hughes); the global chemical injection pump market for oil and gas applications is estimated at several hundred million dollars per year, reflecting the widespread use of continuous chemical injection in virtually every producing well and pipeline system that requires corrosion, scale, hydrate, or biological management. The development of remote-controlled and remotely monitored dosing pump systems with satellite or cellular data communication has significantly improved the management of chemical injection at remote production sites, allowing injection rates, pump stroke counts, alarm conditions, and chemical tank levels to be monitored from a central control room without requiring regular site visits solely for pump adjustment and inspection; this capability is particularly valuable in extended-reach onshore plays (Permian Basin, Bakken, DJ Basin) and offshore unmanned platforms where the cost of personnel visits is high relative to the treatment chemical cost.
What Is a Dosing Pump?
A dosing pump (or metering pump) is a positive-displacement pump that delivers precisely controlled, low-volume flow rates of chemical additives against the operating pressure of the downstream system. In oil and gas operations, dosing pumps inject corrosion inhibitors, scale inhibitors, biocides, hydrate inhibitors, H2S scavengers, and demulsifiers at ppm-level concentrations into production streams, wellbores, and pipelines. Diaphragm dosing pumps are preferred for hazardous chemicals (zero-leakage design); plunger pumps are preferred for high-pressure subsea injection. Flow rate is controlled by stroke frequency, stroke length, or electronic variable-speed drive, with DCS integration for automatic treat rate adjustment as production conditions change.
Synonyms and Related Terminology
Dosing pump is also called a metering pump, chemical injection pump, or proportioning pump. Related terms include chemical injection (the process of adding treatment chemicals to produced fluids, wellbores, or pipelines at controlled rates to prevent or mitigate corrosion, scale, hydrate formation, biological growth, emulsification, or other production chemistry problems; dosing pumps provide the controlled flow rate required for accurate, economical chemical injection), diaphragm pump (a type of positive-displacement pump in which a flexible membrane (diaphragm) separates the pumped fluid from the mechanical drive; prevents chemical contact with drive components and eliminates shaft seal leakage; the preferred design for hazardous or corrosive chemical injection in oilfield applications), injection rate (the volumetric flow rate at which a chemical is injected into the process stream, typically expressed in liters per hour or gallons per day; the injection rate is set to achieve the target treatment concentration (ppm) in the process fluid; dosing pump setpoints are adjusted as production rates change to maintain constant ppm concentration), treat rate (the concentration of a treatment chemical in the produced fluid or injection stream, expressed in parts per million (ppm) by volume or weight; determined from laboratory minimum effective concentration (MEC) testing and adjusted for field conditions; the dosing pump must deliver sufficient chemical volume to maintain the treat rate against the full produced fluid flow rate), and chemical injection mandrel (a downhole completion component (side-pocket mandrel with a check valve) that allows chemical injection from the surface into the production tubing at a specific depth; paired with a surface dosing pump that delivers chemical through a capillary line from the surface to the mandrel injection point).