Rising 3- and 6-rpm Readings: What Is Changing in Your Fluid?
A sustained rise in 3- and 6-rpm readings tells the drilling team that the fluid’s low-shear response is changing. The operator’s next decision is what to check before selecting a treatment. Solids accumulation, recent additions, temperature changes and changes in oil-based mud condition can all be relevant. RheoSense trends help identify when the change started and whether it persists; targeted tests and operating records help establish the cause.
Why the rise matters
The aim is to keep the fluid within the range required for the well. More low-shear structure can support suspension, but higher readings are not automatically better. Excessive rheology can increase pressure losses, depending on the full flow curve, flow rate and well geometry. The 3- and 6-rpm readings alone do not establish hole-cleaning performance, equivalent circulating density or static suspension behaviour. Review the full rheology profile and gel strengths alongside the drilling conditions. [1]
First compare on the same basis
Check that the trend represents the same fluid stream and comparable measurement conditions. Align timestamps, sampling location and temperature basis. For manual comparisons, use consistent sample preparation and test temperature. Temperature and shear history can affect rheology. A return-line trend and a suction-tank sample may describe different fluid at different times, particularly during treatments or transfers. [2]
Investigate solids accumulation
Drilled solids entering the circulating system can contribute to increased viscosity and gel strengths. A persistent rise warrants a review of solids-control performance, dilution and the fluid’s solids content. Low-gravity solids are not synonymous with drilled solids: they can also include intentionally added materials such as bentonite. [3, 4]
Review the retort results and the mud engineer’s solids calculations using the relevant density, salinity and formulation information. Check recent weighting and solids additions. A density increase alone does not quantify low-gravity solids. The operator value is a better basis for deciding whether solids removal, dilution or another response is appropriate, rather than assuming every rise requires a rheology treatment. [4]
Laboratory test shows the effect of fine shale
Deville, Fritz and Jarrett tested a water-based mud with finely ground shale cuttings (median particle size below 10 microns). The equally aged samples show both 3- and 6-rpm readings increasing with added low-gravity solids (LGS). [8]
Figure 1. Laboratory fines-addition test, replotted from SPE 140868, Table 3. All three samples were aged for 48 hours at 400°F and measured at 120°F. Percentages follow the source labels. [8]
Operator value: a sustained rise gives the team a reason to check solids content and solids-control performance. Combine the trend with retort/LGS calculations, treatment and temperature records before choosing solids removal, dilution or another response. Then use the trend to assess the response.
This is laboratory evidence for one water-based formulation, not a real-time well record or an alarm threshold. The readings alone do not measure fines concentration. The study reports that the fluid retained useful performance; it does not establish filter-cake damage or stuck-pipe risk.
Field example A shows a sustained rise in OBM
In this anonymized oil-based mud (OBM) field example, both low-shear readings rise over several hours. Temperature also changes. The trend makes the timing and persistence visible, but does not establish the cause. [9]
Figure 2. Anonymized OBM field measurements, plotted against elapsed time. Values are approximate, replotted from report traces. Temperature is converted to °C. [9]
Operator value: use the onset and duration of the rise to focus the investigation. Compare the trend with temperature, fluid additions and transfers; review solids/retort results and, for OBM, emulsion and wetting checks. Then follow the response to an agreed action.
Fines buildup is not confirmed. Matched solids and treatment records are not available to verify that explanation. The laboratory test illustrates a possible mechanism in WBM; it does not diagnose this OBM event. This example shows a measured trend, not a verified operational outcome.
Field example B shows a higher sustained level in WBM
In this anonymized water-based mud (WBM) field example, both low-shear readings move to higher levels, with shorter excursions along the way. The recorded inlet temperature also changes, so this is not a constant-temperature comparison. [10]
Figure 3. Anonymized WBM field measurements, plotted against elapsed time. Recorded values are shown without smoothing, with inlet temperature in °C. [10]
Operator value: distinguish a lasting shift from a short excursion and identify the periods to compare with mixing, transfers and solids-control activity. Use targeted fluid tests to decide whether an intervention is needed, then track the response against the agreed operating range.
Fines buildup is not confirmed. Matched solids, retort and treatment records are not available to establish the cause. These examples show how to follow a change over time; they do not establish verified operational outcomes or a like-for-like comparison of the two fluids.
Check oil-based mud condition
In an invert-emulsion oil-based mud, rheology can change when the emulsion condition or solids wetting changes. These are related but distinct properties: the emulsion holds water droplets in the continuous oil phase, while oil-wetting concerns the surfaces of solids. Water contamination, reduced emulsion stability and water-wet solids can occur alongside high viscosity. None is established by rising 3- and 6-rpm readings alone. [5]
Review electrical stability (ES) as a trend under consistent test conditions, together with the oil/water ratio and treatment history. Where relevant to the fluid programme, examine HPHT filtration results and perform wetting checks. ES provides evidence about emulsion and wetting qualities, but it is not a direct, standalone measure of either. This combined review helps the mud engineer distinguish a formulation issue from a solids-management issue. [6, 7]
Connect the change to treatments and transfers
A rise may be the intended response to a viscosifier addition or a change in fluid composition. Compare its timing with mixing, transfers, dilution and temperature changes. Allow for the time required for mixing and circulation before judging the response. A matching timestamp is a lead to investigate; confirmation comes from the fluid tests and the subsequent trend.
Use the trend to improve the next decision
RheoSense measurements, reviewed in RheoView and alongside manual results in RheoReport, give the team a record to work from. Use that record to define the period to investigate, select the tests that can distinguish the likely causes, and review the response to an agreed action. Log the treatment time and amount so that the next shift can follow the same evidence.
For operators, the practical value is earlier visibility of a sustained change, a clearer basis for treatment decisions and a shared record of whether the fluid moved back towards the agreed range. Apply the response within the well’s fluid programme and review it with the mud engineer and drilling team.
References
[9] IMS. Anonymized OBM field measurements. Source record retained internally.
[10] IMS. Anonymized WBM field measurements. Source record retained internally.
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