Author: Arella Sun Publish Time: 2026-10-27 Origin: Unionchem
Polyanionic cellulose (PAC) is a cellulose-derived polymer used in water-based drilling fluids to help control filtration and improve the quality of the filter cake. Depending on the grade, it can also contribute substantially to fluid viscosity. The central purchasing decision is therefore not simply whether a drilling fluid needs PAC. It is which PAC grade provides the required fluid-loss control without creating an unwanted rheology or mixing problem.
For many systems, PAC-LV is a starting point when fluid-loss control is needed with a limited increase in viscosity. PAC-HV may be more appropriate when the formulation also needs a stronger viscosity contribution. Neither designation guarantees performance in a particular mud: base-fluid chemistry, solids content, salinity, temperature exposure, and the supplier’s test methods all affect the result.
Terminology: In this article, PAC means polyanionic cellulose. It does not mean polyaluminum chloride, which is also abbreviated “PAC” in other industries.
Selection question | PAC-LV is often worth screening when… | PAC-HV is often worth screening when… |
Primary objective | Reduce filtrate volume while limiting additional viscosity | Combine filtration control with a meaningful viscosity contribution |
Existing mud rheology | The system already has sufficient viscosity | The system needs additional body or suspension support |
Pumping constraints | Excess viscosity could increase operational difficulty | The system can accommodate the resulting rheology |
Evaluation priority | Fluid loss and filter cake at acceptable rheology | Fluid loss, filter cake, and the full rheology profile |
These are screening directions, not interchangeable product specifications. PAC-LV and PAC-HV grades can differ between suppliers. Compare actual test data under a common procedure before treating two products with the same label as equivalents.
During drilling, pressure can force the liquid phase of a mud into a permeable formation. Solids and polymers left behind form a filter cake on the wellbore wall. Effective fluid-loss control aims to limit filtrate invasion while producing a filter cake compatible with the operation.
PAC helps by modifying the fluid phase and contributing to filter-cake formation. Its value should be assessed through several connected outcomes:
Filtrate volume: How much liquid passes through the test medium under defined conditions?
Filter-cake quality: Is the cake reasonably thin, consistent, and appropriate for the system?
Rheology: How does PAC affect plastic viscosity, yield point, gel strengths, and low-shear behavior?
Mixing efficiency: Does it disperse and hydrate reliably with available equipment?
Compatibility: Does it work alongside the system’s salts, clay, starch, xanthan gum, lubricants, and other additives?
A product that produces a low filtrate result in a simple laboratory slurry may not be the best choice if it creates excessive viscosity or hydrates poorly in the field mud. The useful benchmark is performance in the intended fluid system, not the lowest isolated fluid-loss number.
The “LV” and “HV” labels describe the grade’s intended viscosity contribution: low viscosity and high viscosity. Both types may contribute to filtration control, but they give formulators different ways to balance fluid loss and rheology.
If a mud has acceptable rheology but loses too much filtrate, PAC-LV is a logical candidate. The goal is to improve filtration behavior without unnecessarily increasing circulating viscosity.
That distinction matters in systems where adding more polymer could complicate pumping, change solids transport behavior, or require further formulation adjustments. “Low viscosity,” however, does not mean “no rheological effect.” Measure the change in the complete mud.
PAC-HV can be useful when the fluid needs filtration control and an additional viscosity contribution. It may reduce the need to obtain those functions from separate additives, depending on the system.
The trade-off is that a grade selected for its strong viscosity response can overshoot the rheology target. Before choosing it, check not only filtrate volume but also the drilling fluid’s full flow profile before and after aging.
Replacing PAC-LV with PAC-HV—or switching suppliers within either category—should trigger a new formulation trial. A matching label does not establish matching polymer behavior, and similar results at one dosage do not guarantee similar results after salinity or temperature exposure.
The water used to prepare a drilling fluid can materially affect additive performance. A result obtained in fresh water should not automatically be applied to seawater or a concentrated brine.
When screening PAC for a saline system, prepare trials using representative makeup water and salt concentrations. Record when salts are added relative to PAC; addition order can influence dispersion and hydration.
A drilling fluid may experience conditions that differ significantly from a room-temperature bench test. If thermal exposure is relevant, compare samples before and after an aging procedure appropriate to the project.
Report the aging temperature, duration, fluid composition, and testing procedure. A statement that PAC is “temperature stable” is not useful without the conditions under which that conclusion was reached.
Reactive clay, drilled solids, weighting material, and other suspended particles influence both filtration and rheology. Test PAC in a representative solids system rather than assuming that results from a clean polymer solution will carry over to the working mud.
PAC is commonly evaluated alongside other water-based mud additives. Their combined effects are not always the sum of their separate effects. If the formulation contains xanthan gum, starch, CMC, or other polymers, run combination trials at the intended concentrations and mixing sequence.
A supplier comparison should begin with a common test plan. Otherwise, two data sheets may appear comparable while using different water compositions, dosages, mixing times, aging procedures, or filtration tests.
Request the following information for each candidate grade:
Information to request | Why it matters |
Grade designation and intended use | Establishes whether the offer is PAC-LV, PAC-HV, or another grade |
Test method for viscosity and filtration | Makes supplier data comparable |
Test-fluid composition | Shows whether the results are relevant to the target mud |
Dosage used in reported tests | Prevents misleading comparisons at unequal concentrations |
Rheology before and after addition | Identifies unwanted viscosity changes |
Filtrate volume and filter-cake observations | Evaluates the primary filtration objective |
Aging conditions, if tested | Shows what temperature claims actually mean |
Particle-size or handling information | Helps assess dispersion and make-up behavior |
Lot-specific certificate of analysis | Connects the supplied material to the approved specification |
Change-control and traceability process | Supports repeatability after the first order |
Where relevant, buyers can ask suppliers how their test program relates to API 13A specifications and methods used to test water-based drilling fluids, such as those described in API Recommended Practice 13B-1. Those references should be used precisely: testing a product using an API-related method is not the same as claiming that a company or product is “API certified.”
If an API designation is a contractual requirement, specify the applicable edition, grade, test criteria, and evidence required in the purchase documentation.
A controlled comparison does not have to begin with a complicated formulation program. It does need to isolate the decisions that matter.
Prepare the intended mud without the candidate PAC. Record its composition, mixing procedure, initial rheology, filtrate result, and filter-cake observations.
Screen PAC-LV and PAC-HV at the same selected concentration points. Use identical makeup water, addition order, shear input, and hydration time. This reveals the different rheology contributions more clearly than testing each product under a supplier-chosen procedure.
For each sample, document:
filtration result;
filter-cake appearance and thickness, where measured;
rheology at the defined test temperature;
dispersion or lumping observations;
any change after the specified aging procedure.
Once a grade shows promise, refine its dosage. The winning material is not necessarily the one with the lowest filtrate result at the highest concentration. It is the one that meets the filtration requirement while keeping the rest of the mud within its operating window.
Before relying on one approved sample for recurring supply, agree on release specifications, test methods, lot identification, and the procedure for handling an out-of-trend shipment.
Observation | Possible cause | First check |
Filtration remains too high | Dosage or grade is unsuitable; competing effects from the base fluid | Recheck test conditions and compare grades in the actual mud |
Viscosity rises too much | PAC-HV or total polymer loading exceeds the formulation target | Review the full rheology profile and screen PAC-LV |
Powder forms lumps | Addition is too fast or mixing is inadequate | Adjust dispersion method and addition sequence |
Bench test passes, field result differs | Makeup water, solids, shear, or hydration time changed | Recreate field conditions in the lab |
Performance drops after aging | The selected grade or system does not tolerate the test conditions | Review the aging protocol and screen alternatives |
Repeat orders behave differently | Test methods or commercial lots are not adequately controlled | Compare lot-specific COAs and retained samples |
Do not automatically respond to every poor filtration result by adding more PAC. First confirm whether the problem lies in polymer concentration, solids control, water chemistry, mixing, aging, or the test procedure itself.
No—not without testing.
PAC and CMC are related cellulose-derived materials, but commercial grades can differ in substitution, viscosity behavior, and application performance. A buyer should compare their actual drilling-fluid results, not assume that either name guarantees a particular level of salt tolerance or filtration control.
Xanthan gum is often selected when low-shear rheology and suspension are central concerns. PAC is commonly selected for filtration control, with its viscosity contribution depending on grade. They may be used together in a water-based mud, but the combination should be evaluated for both filtration and rheology.
If the problem is primarily excessive filtrate with otherwise acceptable viscosity, begin by screening a fluid-loss-control option such as PAC-LV. If suspension and low-shear performance are also inadequate, examine the whole additive package rather than expecting one polymer to solve every requirement.
Before placing a commercial PAC order, confirm these points in writing:
Is the offered product polyanionic cellulose, and is it designated PAC-LV or PAC-HV?
Which test methods and editions are used for specification and application data?
What water composition and PAC dosage were used to generate the reported results?
What are the measured effects on both filtration and rheology?
Has the grade been tested in the intended saline, clay-containing, or weighted system?
Are temperature-related claims backed by a stated aging procedure?
Can the supplier provide a lot-specific COA, TDS, and SDS?
How are commercial lots traced to the approved sample and release specification?
What packaging and storage conditions are recommended?
What are the confirmed MOQ, lead time, Incoterm, and complaint-handling process for the quoted order?
PAC stands for polyanionic cellulose. It is used in water-based drilling fluids primarily for filtration control and, depending on the grade, viscosity contribution. It should not be confused with polyaluminum chloride, which shares the same abbreviation in other industries.
Neither is universally better. PAC-LV is often screened when the mud needs filtration control without a large additional viscosity contribution. PAC-HV may be useful when both filtration control and increased viscosity are desirable. Compare them at matched dosages in the actual fluid system.
PAC may be evaluated for saline systems, but suitability depends on the specific grade, salt composition and concentration, and complete mud formulation. Request test data prepared with representative water rather than relying on fresh-water results.
No. A supplier can report results obtained using an API-referenced test method without that statement constituting certification. If a purchase contract requires conformity to a particular API specification, identify the applicable requirements and the evidence the supplier must provide.
Not automatically. PAC and xanthan gum are often selected for different primary functions in drilling fluids. Replacing one with the other requires a fresh assessment of filtration, rheology, suspension, and field handling.
At minimum, compare candidate materials using the same base fluid, dosage points, mixing method, filtration test, and rheology procedure. Add salinity and aging tests when those conditions matter to the project, then confirm that the supplier can reproduce the approved specification in commercial lots.
The most effective way to buy PAC is to define the drilling-fluid problem first. If the system needs better filtration control but already has enough viscosity, PAC-LV is a logical candidate. If it needs both filtration control and more viscosity, PAC-HV may deserve a trial. The final choice must be supported by comparable tests in the intended mud and by a supplier specification that can be maintained across commercial shipments.
For a grade recommendation or quotation, provide Unionchem with the base-fluid composition, target filtrate result, current rheology, salinity, expected temperature exposure, and estimated purchase volume. That information makes it possible to evaluate PAC-LV and PAC-HV against the application rather than selecting by product name alone.
