Are You Measuring the Fluid You Are Actually Circulating?

Article 4 of 8 · Drilling Fluid Monitoring: From Measurements to Decisions

A manually collected mud sample leaves the active tank, travels to the mud laboratory and becomes a rheology result. What connects that result to the much larger volume still circulating through the well?

Earlier articles covered measurement methods, changes between checks and the IMS–Newpark cedar-fibre test. Here, the focus moves to the sample itself: how much is collected, where it comes from and what happens before measurement.

Manual sampling: from pit to test cup

The picture below follows a manually collected sample from the active pit through screening and conditioning to a 350 mL (11.8 US fl oz) Fann 35 test portion. [1]

Figure 1. Manual sampling from the circulating system to the instrument. Volumes are illustrative complete-loop working totals; reserve and storage fluid is excluded.

For manual sampling, three volumes matter: the fluid in the connected circulating system, the amount collected from the pit, and the portion placed in the instrument. The 1 L (33.8 US fl oz) bucket in the illustration supplies the smaller test portion; record the actual volume collected.

The illustration uses assumed working volumes: 700 bbl onshore (300 bbl in active pits and surface lines + 400 bbl in the wellbore), and 2,000 bbl offshore (500 bbl in active pits and surface lines + 600 bbl in the wellbore + 900 bbl in the marine riser). For an actual comparison, use measured active pit levels and connected line, drillstring, annulus and riser volumes; exclude isolated reserve and storage tanks. [2]

A small sample can represent a well-mixed stream. The volume contrast shows scale; sampling location and handling determine how well that sample represents the fluid of interest.

Manual sample preparation and measurement

Collect. Take the sample from the top of the active pit with the 1 L bucket on a rod. Record the tank compartment, collection time and volume, together with circulation, mixing or treatment activity.

Transfer. Take the identified sample to the mud laboratory using the site procedure. Keep it protected and note any delay or visible separation. Distinguish collection time from test time and data-entry time.

Prepare. Screen coarse particles where the test procedure requires it, then rehomogenize the sample and establish the test temperature. Record screening, mixing and standing time so the preparation can be compared. [1,4]

Measure. Use the 350 mL test portion and record the actual temperature, test time and instrument configuration with the results. These details connect the reading to the conditions under which the sample was tested.

View RheoSense trends in RheoView

A manual sample represents the fluid collected at a particular place and time. For comparison with RheoSense measurements, identify the corresponding stream and allow for sample transport and measurement-cycle delay. Where sampling points are on opposite sides of the well, account for circulation time.

RheoView provides the visual context: check the selected stream and time window, then relate the manual collection and test times to the surrounding RheoSense trend.

Figure 2. RheoView displays RheoSense measurement trends for the selected stream. Anonymized interface illustration.

Align manual samples with RheoSense trends

RheoReport brings manual test inputs and RheoSense measurements together on the same time axis. The teal arrows in this 24-hour client report identify manual entries alongside the RheoSense trends. [5]

Figure 3. Manual test inputs and RheoSense measurements reported to the client through RheoReport. [5]

Sustained changes in RheoSense readings

A separate RheoReport example below compares return-side RheoSense measurements with the manual values included in that client report. The 6 rpm data are referenced to 150°F (65.6°C). [3]

Figure 4. RheoSense measurements and manual values reported to the client through RheoReport. [3]

The blue RheoSense trace shows sustained changes in the 6 rpm reading, while the orange dashed line shows the manual values included in the client report. The RheoSense reading remains above the displayed manual value for about five hours, followed by nearly five hours below it.

The sustained rise and fall show why the timeline matters. Linking the report to collection times, sample preparation and operating activity gives the mud engineer a practical basis for reviewing the changes.

Comparing manual and RheoSense readings

Keep the manual sample source and volume, collection and test times, preparation, temperature and operating events in one record. Match that record to the RheoSense measurement period. If readings differ, these details give the next shift a clear starting point for a repeat check or investigation.

This emphasis on preparation is consistent with API RP 13I, which identifies agitation history and test temperature as important influences on fluid properties. [4]

Contact IMS to discuss sampling points and a comparison plan for your fluid system.

References

[1] Fann. Model 35 Viscometer Instruction Manual, revision P, January 2016. Section 5: pre-stirred sample and 350 mL cup portion.

[2] SLB Energy Glossary. Circulation system. Components of the connected fluid circuit.

[3] IMS. RheoSense return-side measurement data reported to the client through RheoReport.

[4] API. RP 13I: Laboratory Testing of Drilling Fluids. Public scope description: effects of agitation history and test temperature.

[5] IMS. 24-hour RheoReport client example containing RheoSense measurements and manual test inputs.