{"id":15417,"date":"2026-09-22T06:37:45","date_gmt":"2026-09-22T06:37:45","guid":{"rendered":"https:\/\/tenessy.com\/?p=15417"},"modified":"2026-09-22T06:37:47","modified_gmt":"2026-09-22T06:37:47","slug":"polyanionic-cellulose-pac-in-oil-drilling-fluids-complete-guide","status":"publish","type":"post","link":"https:\/\/tenessy.com\/el\/polyanionic-cellulose-pac-in-oil-drilling-fluids-complete-guide\/","title":{"rendered":"Polyanionic Cellulose (PAC) in Oil Drilling Fluids: Complete Guide"},"content":{"rendered":"
\"PAC\"
<\/figcaption><\/figure>\n\n\n\n

\u03a0\u03bf\u03bb\u03c5\u03b1\u03bd\u03b9\u03bf\u03bd\u03b9\u03ba\u03ae \u03ba\u03c5\u03c4\u03c4\u03b1\u03c1\u03af\u03bd\u03b7 (PAC) <\/u><\/a>in oil drilling fluids is the preferred fluid-loss control and rheology additive for water-based mud systems, delivering stable filtration control in fresh water, seawater, and saturated brine at temperatures up to 120 \u00b0C. This guide explains how PAC-LV and PAC-HV differ, how they pass API\/ISO 13500 testing, and how to dose them for optimized drilling performance in every water chemistry.<\/p>\n\n\n\n

\u0395\u03b9\u03c3\u03b1\u03b3\u03c9\u03b3\u03ae<\/strong><\/h2>\n\n\n\n

Fluid loss is the quiet killer of drilling economics. When drilling mud leaks into permeable formations, the filter cake thickens, the hole begins to stick, formation damage sets in, and the mud bill climbs. Polyanionic cellulose (PAC) is the additive drilling-fluid engineers reach for when they need predictable, temperature-stable filtration control across the widest range of water chemistries \u2014 from fresh water to saturated brine.<\/p>\n\n\n\n

Polyanionic cellulose (PAC) is a high-purity, high degree-of-substitution carboxymethyl cellulose (CMC). The carboxymethyl groups (up to DS 0.9\u20131.3, far higher than standard CMC) make the molecule strongly anionic, highly soluble, and resistant to the salt that deactivates ordinary CMC. PAC comes in two functional grades that solve different problems: PAC-LV (low viscosity) for filtration control with minimal viscosity contribution, and PAC-HV (high viscosity) for filtration control plus viscosity and cuttings suspension. Most field muds use both, tuned to the density, water chemistry, and temperature of the well.<\/p>\n\n\n\n

\u03a3\u03c4\u03bf TENESSY Chemical<\/u><\/a>, we manufacture PAC from premium cotton-derived cellulose on German process equipment, with production control aligned to API 13A \/ ISO 13500 testing methods. Our PAC grades are exported to 40+ countries and used in both land and offshore drilling operations. This guide distills the field experience behind PAC selection: the mechanism of filtration control, the LV vs. HV decision, performance in every water type, and practical dosage programs.<\/p>\n\n\n\n

The Role of PAC in Drilling Fluids: Filtration, Viscosity, and Rheology<\/strong><\/h2>\n\n\n\n

Fluid-Loss Control: The Filter Cake Mechanism<\/strong><\/strong><\/h3>\n\n\n\n

Fluid loss is the volume of mud filtrate that escapes into the formation under pressure. In a standard API filtration test (API 13B-1, LPLT, 690 kPa \/ 100 psi over 30 minutes), a good PAC-treated mud gives 5\u20138 mL filtrate, versus 15\u201340 mL or more for an untreated or starch-only mud.<\/p>\n\n\n\n

Polyanionic cellulose (PAC)controls this loss through the filter cake. The polymer chains adsorb onto the surfaces of clay particles (bentonite) and drill solids, bridging them into a thin, low-permeability cake on the wellbore wall. Because the cake is thin and pliable, it limits both the volume of filtrate and the risk of a stuck pipe. Two properties make PAC the right polymer for this job:<\/p>\n\n\n\n

    \n
  • High anionic charge.<\/strong>\u00a0The carboxymethyl groups adsorb strongly onto positively charged clay edges and onto the calcium\/magnesium sites on formation rock, so the cake binds firmly even in brines.<\/li>\n\n\n\n
  • Chain extension.<\/strong>\u00a0In solution, PAC’s charged chains repel each other and stay extended, so even a small dosage covers a large surface area of clay. This is why PAC outperforms starch (which is neutral and leaches out of the cake) and ordinary CMC (which coils up in brine and loses effectiveness).<\/li>\n<\/ul>\n\n\n\n

    Viscosity and Suspension<\/strong><\/h3>\n\n\n\n

    PAC-HV raises the mud’s viscosity by entangling in the water phase, which does three jobs:<\/p>\n\n\n\n

      \n
    • Cuttings transport.<\/strong>\u00a0The annulus must carry drilled cuttings to the surface; a viscosity minimum is required to keep them moving. At low shear rates (5\u2013100 s\u207b\u00b9, the range of the annulus), PAC-HV builds the gel-like structure that suspends cuttings when circulation stops.<\/li>\n\n\n\n
    • Hole cleaning in deviated wells.<\/strong>\u00a0In horizontal and deviated sections, cuttings settle on the low side of the hole. The low-shear viscosity from PAC-HV is the main defense.<\/li>\n\n\n\n
    • Barite suspension.<\/strong>\u00a0Weighted muds rely on a yield stress to keep barite (density 4.2 g\/cm\u00b3) suspended when pumps are off. PAC-HV contributes to that yield stress.<\/li>\n<\/ul>\n\n\n\n

      Rheological Control and Temperature Stability<\/strong><\/h2>\n\n\n\n

      Polyanionic cellulose (PAC) is thermally robust for a biopolymer: it maintains its filtration and viscosity performance up to about 120 \u00b0C (some high-DS grades to 130 \u00b0C) in low-solids muds, and it is compatible with the common rheology modifiers \u2014 xanthan gum for low-shear viscosity, polyacrylamide-based shale inhibitors, and lignosulfonate thinners. Unlike xanthan, PAC does not shear-degrade catastrophically in the bit nozzles, and unlike starch, PAC does not ferment or thin out in hot, oxygenated mud. Its resistance to bacteria is another practical advantage: starch needs biocide treatment, PAC does not.<\/p>\n\n\n\n

      The typical field combination is PAC-LV for filtration + xanthan or PAC-HV for viscosity, with the ratio set by the mud density and hole angle. A straightforward rule of thumb is covered in the dosage section below.<\/p>\n\n\n\n

      \"\u03c3\u03c5\u03b3\u03ba\u03cc\u03bb\u03bb\u03b7\u03c3\u03b7\"
      <\/figcaption><\/figure>\n\n\n\n

      PAC-LV vs PAC-HV: What’s the Difference and Which One Do You Need?<\/strong><\/h2>\n\n\n\n
      \u03a0\u03b1\u03c1\u03ac\u03bc\u03b5\u03c4\u03c1\u03bf\u03c2<\/strong><\/strong><\/td>PAC-LV<\/strong><\/strong><\/td>PAC-HV<\/strong><\/strong><\/td><\/tr>
      Primary function<\/td>Fluid-loss control<\/td>Fluid-loss control + viscosity<\/td><\/tr>
      Typical viscosity (1% solution in brine, Brookfield)<\/td>30\u2013120 mPa\u00b7s<\/td>500\u20131,200 mPa\u00b7s<\/td><\/tr>
      Filtrate control (API LPLT, 30 min)<\/td>5\u20138 mL<\/td>6\u201310 mL<\/td><\/tr>
      Effect on mud rheology<\/td>\u0395\u03bb\u03ac\u03c7\u03b9\u03c3\u03c4\u03bf<\/td>Significant (builds structure)<\/td><\/tr>
      Best in<\/td>Low-solids muds, brine muds, weighted muds<\/td>Unweighted and lightly weighted muds, vertical sections<\/td><\/tr>
      Typical dosage (per m\u00b3 of mud)<\/td>2\u20138 kg<\/td>1\u20136 kg<\/td><\/tr>
      \u0391\u03bd\u03bf\u03c7\u03ae \u03c3\u03c4\u03bf \u03b1\u03bb\u03ac\u03c4\u03b9<\/td>Excellent (saturated brine)<\/td>\u0395\u03be\u03b1\u03b9\u03c1\u03b5\u03c4\u03b9\u03ba\u03cc<\/td><\/tr>
      \u0398\u03b5\u03c1\u03bc\u03b9\u03ba\u03ae \u03c3\u03c4\u03b1\u03b8\u03b5\u03c1\u03cc\u03c4\u03b7\u03c4\u03b1<\/td>Up to ~120\u2013130 \u00b0C<\/td>Up to ~120 \u00b0C<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

      The selection logic is simple once you know the mud program:<\/p>\n\n\n\n

        \n
      • PAC-LV is the filtration specialist.<\/strong>\u00a0It is chosen when the mud already has enough viscosity from bentonite, xanthan, or solids, and the only gap is fluid loss. This is the common case in weighted muds, where adding a high-viscosity polymer would push yield stress and pump pressure too high.<\/li>\n\n\n\n
      • PAC-HV is the dual-purpose additive.<\/strong>\u00a0It is used in low-solids, unweighted muds (where there is no bentonite to build viscosity) and in vertical-hole sections where the mud needs viscosity but no extra density. PAC-HV adds viscosity and filtration control with a single product.<\/li>\n<\/ul>\n\n\n\n

        Most mud systems use both.<\/strong><\/strong> A typical field recipe for a fresh-water low-solids mud starts with 4\u20136 kg\/m\u00b3 PAC-LV plus 1\u20133 kg\/m\u00b3 PAC-HV; a saturated-brine completion brine uses 5\u20138 kg\/m\u00b3 PAC-LV alone, because no polymer viscosity is wanted in a completion fluid.<\/p>\n\n\n\n

        PAC Performance in Fresh Water, Seawater, and Saturated Brine<\/strong><\/h2>\n\n\n\n

        he defining test for a fluid-loss polymer is its performance in salt. Ordinary CMC loses most of its viscosity and filtration control in brines because salt shields the polymer’s charges and coils the chains. PAC, built with higher DS and higher purity, keeps its chains extended even in saturated NaCl.<\/p>\n\n\n\n

        Fresh-Water Muds<\/strong><\/h3>\n\n\n\n

        In fresh water, Polyanionic cellulose (PAC)\u00a0disperses and hydrates quickly. A typical fresh-water mud with 4% bentonite + 4 kg\/m\u00b3 PAC-LV gives an API filtrate of 6\u20138 mL\/30 min and a plastic viscosity increase of only 1\u20133 mPa\u00b7s \u2014 filtration control with almost no rheology penalty. This is the classic application for PAC-LV in low-solids muds, where the filtration spec is met while the mud stays thin enough to drill fast.<\/p>\n\n\n\n

        Seawater and High-Salinity Muds<\/strong><\/h3>\n\n\n\n

        Seawater (about 3.5% total salts) and mixed-salt muds are where PAC separates from CMC. At 3.5% NaCl, standard CMC retains only 40\u201360% of its fresh-water viscosity; PAC retains 70\u201390% because its higher DS keeps the chains ionized. Filtration control remains in the 6\u20139 mL range. Field practice is to raise PAC-LV dosage by 20\u201330% when the mud system switches from fresh to seawater to compensate for the remaining viscosity loss.<\/p>\n\n\n\n

        Saturated Brine (NaCl \u2265 36%)<\/strong><\/h3>\n\n\n\n

        Saturated-brine muds and completion brines are the harshest environment. The mud is nearly a dead salt solution, and most polymers either precipitate or gel. PAC at 5\u20138 kg\/m\u00b3 delivers an API filtrate of 8\u201312 mL\/30 min in saturated NaCl \u2014 acceptable for most drilling operations and far better than starch, which gives 15\u201325 mL and degrades. For completion brines (where no filter cake on the producing formation is desired), PAC-LV is used specifically because it builds a thin, acid-soluble cake that cleaning fluids can remove. Note that PAC is used in monovalent brines; for divalent brines (CaCl\u2082, CaBr\u2082, ZnBr\u2082) above about 10%, PAC’s performance degrades and specialist polymers are required.<\/p>\n\n\n\n

        Water type<\/strong><\/strong><\/td>PAC-LV dosage (kg\/m\u00b3)<\/strong><\/strong><\/td>API LPLT filtrate (mL\/30 min)<\/strong><\/strong><\/td>\u03a3\u03b7\u03bc\u03b5\u03b9\u03ce\u03c3\u03b5\u03b9\u03c2<\/strong><\/strong><\/td><\/tr>
        Fresh water<\/td>3\u20135<\/td>5\u20138<\/td>Add to 4% bentonite mud<\/td><\/tr>
        Seawater \/ 3.5% salt<\/td>4\u20136<\/td>6\u20139<\/td>Increase dosage ~25% vs fresh<\/td><\/tr>
        10\u201320% NaCl<\/td>5\u20137<\/td>7\u201310<\/td>Use high-DS PAC grades<\/td><\/tr>
        Saturated brine<\/td>5\u20138<\/td>8\u201312<\/td>PAC-LV preferred; acid-soluble cake<\/td><\/tr>
        KCl-polymer muds<\/td>3\u20136<\/td>5\u20138<\/td>Pairs with shale inhibitors<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

        API and ISO Testing Standards for PAC<\/strong><\/h2>\n\n\n\n

        Drilling-fluid additives are bought to standards, not to datasheets. PAC grades are tested and certified according to:<\/p>\n\n\n\n