Selecting an all-metal conical screw pump requires matching its performance to the viscosity of the fluid it handles. Viscosity affects internal leakage, flow resistance, torque demand, and efficiency.

A published viscosity capability alone is therefore insufficient to determine whether a pump can deliver the required flow at an acceptable operating load. Research on all-metal conical screw pumps shows that viscosity changes how clearance and rotational speed influence these performance measures.

Viscosity should be evaluated under actual pumping conditions, rather than inferred directly from a laboratory value obtained under different or unverified conditions. Relating the reported viscosity to the fluid temperature and condition at the pump intake provides a sounder basis for assessing pump suitability and identifying any additional data required for selection.

How Does Viscosity Affect All-Metal Conical Screw Pump Performance?

Viscosity affects both leakage through the rotor–stator clearance and resistance to fluid movement within the pump. These effects must be evaluated together when assessing delivered flow, torque demand, and efficiency.

A 2025 study published in Scientific Reports investigated how fluid viscosity, clearance, and rotational speed influence all-metal conical screw pump performance through numerical simulation supported by outdoor testing.

Evaluate Flow, Torque and Efficiency Together

The study found that lower-viscosity fluids were more sensitive to leakage as clearance increased. With more viscous fluids, leakage increased less rapidly, while resistance within the pump became more significant to the energy balance.

Consequently, a configuration that meets the required flow rate may not provide the most favourable torque demand or energy efficiency. These performance measures require separate assessment before a configuration is recommended.

The speed analysis illustrates this distinction. At a fixed clearance of 0.1 mm, displacement increased approximately linearly with rotational speed, but efficiency followed different trends at different viscosities. Under the more viscous conditions investigated, torque increased more sharply and energy efficiency declined as speed increased.

Pump selection must therefore account for the operating load associated with the required flow and pressure duty. Increasing speed does not remove the need to match the pump configuration to the fluid conditions.

Match Clearance and Speed to the Fluid Conditions

The research also found that energy efficiency did not decrease consistently as clearance increased. Under some of the more viscous conditions studied, efficiency initially improved before declining as leakage became more significant.

A smaller clearance is therefore not necessarily the most efficient choice across all fluid conditions. Clearance and speed must be considered in relation to viscosity and the required operating duty.

The clearance analysis covered viscosities from 10 to 500 mPa·s. Outdoor validation used water, while the viscosity-dependent findings were obtained through simulation. The results support the relationships between these variables but do not establish universal operating settings for heavy-oil wells.

Which Viscosity Should Guide Pump Selection?

The viscosity used in selection should correspond to the fluid conditions at the pump intake. Reservoir estimates and surface measurements can support that assessment, provided their relationship to the intake conditions is established.

Focus on the Fluid at the Pump Intake

A viscosity value measured at the surface should not automatically be treated as representative of the fluid entering the pump. Its relevance depends on the corresponding temperature and sample condition.

Research modelling temperature and viscosity profiles in a heavy-oil production well demonstrates the importance of this distinction. The study evaluated conditions along a production path equipped with a downhole induction heater, showing that viscosity must be associated with the relevant location and thermal conditions.

These findings support the interpretation of viscosity profiles; they do not establish the performance of a particular pump.

Where intake viscosity is calculated or inferred rather than measured directly, the supporting temperature data, fluid relationship, and assumptions should remain identifiable. This allows the selection assessment to distinguish measured inputs from derived values.

Account for Recorded Operating Variations

A single viscosity value may support an initial assessment without representing the full range of conditions recorded during production.

Available viscosity measurements should be reviewed alongside temperature data and operating records. Where these records identify distinct production periods, the corresponding conditions should be assessed separately rather than represented by one average value.

Recorded conditions, calculated values, and unresolved information gaps must remain distinct. Planned operational changes should also be identified separately so that they are not presented as established production conditions.

Does the Laboratory Report Represent the Pumping Conditions?

The laboratory report provides the measurement basis needed to determine whether a viscosity result is suitable for selection. Test temperature, method, and sample condition should remain associated with each reported value.

Check the Test Temperature and Measurement Basis

An initial technical review requires the viscosity value, unit, test temperature, and available method information. Where measurements exist at several temperatures, the full viscosity–temperature relationship provides a more useful basis for assessment than an isolated result.

A viscosity measured at a lower temperature cannot be assumed to represent pump-intake viscosity without supporting fluid data. The relationship between the test condition and the actual pumping condition must first be established.

Results with incomplete measurement information should remain preliminary. A surface or laboratory value should not be assigned to downhole conditions solely because an intake-specific value is unavailable.

Confirm the Sample Condition

The sample description is equally important. Reports should identify whether the measurement relates to degassed crude, a produced-fluid sample, or another prepared sample condition.

A crude-oil measurement does not necessarily represent the complete produced stream. Available water-content and gas information should therefore be reviewed alongside the sample description and production records.

Unconfirmed sample conditions should be recorded as information gaps rather than incorporated into the selection as assumptions.

How Should a Published Viscosity Capability Be Interpreted?

HXBS's all-metal conical screw pump has a stated viscosity capability of 20,000 mPa·s at 50°C. This reference temperature is an integral part of the specification and must be considered when assessing application suitability.

Where submitted viscosity data correspond to a different temperature, assessment requires the available viscosity–temperature relationship and the actual pump-intake conditions. Direct comparison of values measured under different conditions is insufficient to establish suitability.

Product specifications, laboratory reports, and research results provide different types of evidence. A capability statement describes the stated scope of the equipment; a laboratory result characterises a sample under specified test conditions; a research finding applies to the equipment and conditions investigated.

Accordingly, the simulation results covering viscosities up to 500 mPa·s cannot be extrapolated directly into a performance prediction at 20,000 mPa·s. Nor does a published viscosity capability independently establish the flow, torque, or efficiency achievable in a particular well.

Selection requires these data to be evaluated against the application's flow and pressure requirements.

What Viscosity Information Should You Submit for Pump Selection?

For an initial all-metal conical screw pump assessment, the following information supports a more complete technical review:

• Measured viscosity values and units, with the temperature corresponding to each result.

• A viscosity–temperature curve or multiple temperature points, where available.

• Sample source, sampling date, and the condition recorded by the laboratory.

• Available test-method information, including shear conditions where reported.

• Pump-intake temperature measurements or estimates supported by well data, with the source identified.

• Water-content and gas information relevant to the sample and production conditions.

• Recorded operating variations and planned changes relevant to selection.

• Unconfirmed data and assumptions requiring further review.

These records should accompany the required flow rate, pressure duty, and other relevant well information.

Further testing should address a specific uncertainty affecting selection, such as whether the available viscosity data adequately represent the fluid at the pump’s operating temperature. Providing the original laboratory report preserves the connection between each result and its measurement conditions.

How HXBS Supports All-Metal Conical Screw Pump Selection

At HXBS, we develop and manufacture all-metal conical screw pumps for heavy-oil production, supported by application-specific engineering. Our selection assessment considers viscosity alongside temperature, water content, sand conditions, well depth, and production requirements. Support extends from application review and customised design to installation and ongoing technical service.

For viscosity-related enquiries, we assess the submitted fluid data against the pumping conditions and required duty. A published viscosity limit is considered within that assessment rather than used as an independent selection criterion.

Where the available information is incomplete, we identify the conditions requiring clarification before recommending a configuration. This approach maintains a clear relationship between the application data, the selection assumptions, and the proposed pump duty.

Select for the Fluid Conditions at the Pump

All-metal conical screw pump selection requires viscosity data representative of actual pumping conditions. Suitability depends on whether the proposed configuration can meet the required flow and pressure duty at an acceptable operating load—not simply whether a reported viscosity is below a published limit.

Contact HXBS for an application review and submit your fluid report, pump-intake temperature data, target flow rate, and pressure requirements. Our engineering team can review the available information, identify any additional data needed, and assess a suitable pump configuration for your well.