Short-Lived Fluid Changes: Reading the Rheology and Density Trends

Article 2 of 8 · Drilling Fluid Monitoring: From Measurements to Decisions

Two accurate results from Manual Fann35 samples can still miss a temporary change between them.

Manual Fann35 samples taken before and after a short-lived rheology change can both give accurate results. Yet neither result records what happened in between.

This is a question of coverage over time. Manual Fann35 samples remain valuable. An ongoing record adds the sequence: when a change began, how long it lasted and whether it happened again.

IMS explored this sampling gap in our 2021 article, Is There Always A Straight Line Between Two Points? This follow-up examines short-lived changes in the 3 rpm and 6 rpm trends between Manual Fann35 samples, together with density changes between manual mud-balance measurements. For the measurement principles, see Fann 35 and RheoSense: Spot Measurements and Automated Fluid Monitoring.

The changes between the points

Look at the 3 rpm trace below. Its short peaks and changing level are visible in the trend. A set of Manual Fann35 samples collected only at the highlighted points would leave much of that sequence unrecorded.

Figure 1. The 3 rpm trace shows changes between illustrative Manual Fann35 sampling points. Red markers with yellow outlines illustrate when Manual Fann35 samples might be taken; they are not actual test results.

The 6 rpm trace offers a second view of the same limitation between Manual Fann35 samples. Results at selected times cannot, by themselves, describe every excursion between them.

Figure 2. The 6 rpm trace provides another example of intervening behaviour. Highlighted points illustrate the timing of Manual Fann35 samples; they are not actual test results. Both graphs retain the IMS source traces and axes, with RheoSense labels.

These graphs illustrate temporal coverage. They do not establish measurement accuracy or explain the cause of an excursion.

Density matters between manual mud-balance checks too

Density deserves the same attention as rheology. For a given vertical height of fluid, hydrostatic pressure depends on the fluid density.[3] That makes a record of density changes an important part of understanding the fluid system.

The supplied density plot shows a short, pronounced peak and smaller excursions between the highlighted points. Manual mud-balance measurements made before and after an excursion can both be accurate, while the temporary change remains absent from those two results.

Figure 3. Density trend extracted from the IMS source graph. The original secondary-axis trace is retained. Red markers with yellow outlines illustrate the timing of manual mud-balance measurements; they are not actual test results.

The trend provides a time window for verification and comparison with the operating record. A surface density excursion alone does not quantify a change in downhole pressure; its significance depends on where the fluid was measured and how it moved through the system.

From noticing a change to investigating it

A developing trend gives the team a time window to investigate. Consider a tank transfer or a planned fluid treatment: a recorded excursion can be compared with the operational log and used to guide follow-up Manual Fann35 samples for rheology or manual mud-balance measurements for density. A return towards the earlier level also provides useful context for the next shift.

Those are examples of possible investigations, not identified causes of the changes in these graphs.

Recognising a developing trend creates an opportunity to verify the change and consider a response. For rheology, that verification can include Manual Fann35 samples. This sequence does not specify a detection or response time.

Published work on long lateral wells discusses automated fluid measurement in relation to mixing efficiency and solids accumulation, with fluid properties considered alongside drilling data. The value lies in bringing those records together.[2]

A useful trend needs context

Where was the fluid measured? Fluid entering the well and fluid returning from it have different histories. Circulation time, surface transfers and mixing affect which fluid is being compared. The sampling point and relevant operational events should remain clear in the record.

When does the result represent the fluid? Travel through the supply line, the measurement cycle and averaging can delay or smooth a change. A frequently refreshed display does not mean that every property is a new result. Gaps and stale values need to be visible.

How will the change be checked? When comparing Manual Fann35 samples with RheoSense results, align the sampling time, location, temperature and test procedure. A conditioned Manual Fann35 sample and a flowing sidestream need an agreed basis for comparison.[1]

How RheoSense supports that record

RheoSense draws fluid from a connected part of the mud system and provides automated measurements from that sidestream. Its records can help the team follow rheology changes between Manual Fann35 samples and density changes between manual mud-balance measurements, and review them against the operational timeline. Complete rheology profiles and gel results follow their respective measurement cycles.[1]

Newpark and operators supported by IMS are already using real-time data from IMS.

Manual Fann35 samples remain part of rheology reference checking and targeted investigation. Manual mud-balance measurements provide the corresponding density check. Surface-fluid trends also need to be considered alongside the relevant drilling and well-control information; a surface trend alone cannot establish what is happening downhole.

Which gap matters on your next campaign?

Which change would your team want to see before the next Manual Fann35 sample or manual mud-balance check? A temporary density excursion during a transfer? A treatment response? A developing rheology trend?

Start with that question, then define the sampling point, the response time needed and how the result will be verified.

Contact Intelligent Mud Solutions to discuss your fluid programme and the monitoring gap you want to investigate.

Sources

[1] Intelligent Mud Solutions (4 October 2026). Fann 35 and RheoSense: Spot Measurements and Automated Fluid Monitoring.

[2] Toomes, R. J. and Offenbacher, M. (2024). The 5th Mile: A Review of the Limiters to Reaching Further in Unconventionals. AADE-24-FTCE-059, p. 5. This paper provides general technical context, not validation of an IMS installation.

[3] SLB Energy Glossary. Hydrostatic pressure. Relationship between fluid density, vertical fluid-column height and hydrostatic pressure.

Figures: IMS-supplied graph extracts and conceptual sequence. Highlighted rheology markers illustrate the timing of Manual Fann35 samples; density markers illustrate the timing of manual mud-balance measurements. None are actual manual test results.