Field Notes on Poly Anioniccellulose (PAC): what operators actually ask for

If you’ve spent a week on a rig, you already know the rule: keep filtrate low, keep shales calm, keep costs steady. That’s where Poly Anioniccellulose (PAC) quietly earns its keep. It’s a highly purified, water‑soluble cellulose ether (usually sodium salt), white to light‑yellow, odorless, and yes—soluble in cold and hot water. It’s become the default polymer in salty systems, from onshore salt beds to offshore brines. Many customers say it’s the “no‑drama” additive they trust when wells get tricky.

Industry trends (quick take)

Two clear moves: higher brine salinity tolerance and cleaner formulations. Offshore projects are pushing for predictable fluid loss under high TDS; unconventional plays want better shale integrity without heavy dosing. Actually, we’re also seeing tighter QA—suppliers win bids by showing reproducible API/ISO test data, not just a datasheet blurb.

Typical technical specs (field-friendly)

Note: real‑world use may vary with brine composition, solids loading, temperature, shear history, and biocide/oxidant exposure.

Where it’s used

• Saltwater and offshore drilling fluids (primary fluid‑loss control, shale inhibition assist).
• Workover/completion brines (cleaner filtrate, better formation compatibility).
• Make‑up pills and lost‑circulation blends, when finer bridging and tight filtrate are needed.

How it’s made (short version)

Base cellulose is alkalized, then etherified (introducing anionic carboxymethyl‑type groups) to raise substitution and uniformity. After neutralization and washing, it’s dried, milled, and screened. Labs verify substitution level, purity, and salt‑brine performance.

Testing standards: API RP 13B‑1 for rheology/filtrate, ISO 13500 alignment for drilling‑fluid materials. Some buyers also request microbial count and heavy‑metal screening. Service life: typically 24 months in sealed bags; in fluid systems, performance holds to ~120–150°C (some grades ≈ 160–180°C) depending on salts and oxygen/oxidants.

Advantages you actually notice

• Low filtrate with light dosage, even in high‑TDS brines.
• Smooth rheology—less spiky than some synthetic copolymers, easy to thin/control.
• Clean solids control; fewer high‑molecular tails plugging screens.
• Good compatibility with starches, PAC/CMC blends, and bridging agents.

Vendor landscape (my quick comparison)

Ask for API RP 13B‑1 test sheets per lot, plus salt‑brine viscosity curves. Real‑world results may vary by solids, temperature, and shearing.

Customization and QC

Common options include LV vs. HV grades, tailored degree of substitution, faster-hydrating milling, and anti‑caking packages. QC usually covers moisture, purity, DS, particle size, Brookfield viscosity, API filtrate (with/without salt), and thermal aging (e.g., 16 hr @ 150°C).

Mini case study

Offshore brine system (NaCl 20%): switching from generic polymer to Poly Anioniccellulose (PAC) LV at 6 g/L cut API filtrate from 18 mL to 9 mL and reduced screen blinding. A superintendent told me, “Surprisingly, we used less to get the same flat curve.” Not earth‑shattering, but it saved rig hours on conditioning.

Bottom line: If your fluid program needs predictable low filtrate in salt, Poly Anioniccellulose (PAC) remains a safe, economical lever—especially when you get hard data aligned to API RP 13B‑1 and your actual brine chemistry.

1. API RP 13B‑1: Recommended Practice for Field Testing Water‑Based Drilling Fluids. American Petroleum Institute.
2. ISO 13500: Petroleum and natural gas industries — Drilling fluid materials — Specifications and tests.
3. Drilling Fluids Processing Handbook (G. R. Gray et al.), Elsevier; practical polymer/filtrate guidance.
4. SPE Technical Literature on polymer fluid‑loss control in brines (overview papers; performance vs. salinity and temperature).