Lost Circulation Materials (LCM): Types, Particle Sizing and Pills

Lost circulation materials (LCM) are solids, such as sized calcium carbonate, resilient graphite, ground nut shells, mica flakes and fibers, added to a drilling fluid to seal the fractures, caverns and permeable rock that take whole mud. One loss event can cost up to a million dollars or more (Alsaba et al., AADE-14-FTCE-25, 2014).

Every loss raises the same three questions: which material, which size and how much. LCM keeps the circulating drilling fluid in the hole, and each answer below rests on a named paper, standard or regulation.

LCM falls into eight categories under the 2014 classification, is sized to the opening by seven published rules dated 1977 to 2017, and is dosed by treatment, from a pre-treated active system to a high-concentration pill. Selection follows loss severity, fluid system and hole temperature, and in US offshore waters only the whole mud carrying the LCM faces a discharge limit.

Standards and regulations are checked against their issuing bodies, product values against the named data sheet and figures against the dated source named in the sentence; see our methodology and fact-checking.

What Is a Lost Circulation Material (LCM)?#

A lost circulation material is any substance added to a drilling fluid while the fluid is being lost to formations downhole, and its three classic forms are fibrous, flaky and granular. Fibrous LCM includes cedar bark, shredded cane stalks and mineral fiber. Flaky LCM includes mica and cellophane, and granular LCM includes ground limestone or marble and nut hulls.

The 2014 update of the classification lists eight categories: granular, flaky and fibrous materials, LCM mixtures, acid- or water-soluble LCM, high-fluid-loss squeeze materials, swellable or hydratable combinations and nanoparticles (Alsaba et al., AADE-14-FTCE-25, 2014). Each category is defined by how it plugs an opening, not by its chemistry, which sets LCM apart from the other drilling fluid additive classes. Weighting agents, viscosifiers, fluid-loss additives and LCM each hold one function among the drilling fluid additive classes.

A 1951 grouping already named fibrous, granular, lamellated and dehydratable materials, as cited in AADE-14-FTCE-25. The 2014 scheme keeps the fibrous and granular groups and adds the soluble, swellable and nanoparticle groups.

How LCM differs from other mud additives#

LCM plugs openings that whole mud flows into, while fluid-loss additives reduce the volume of filtrate that passes through the filter cake. Whole mud escapes through fractures and caverns far wider than a pore throat, so LCM particles are sized to those openings, while filtration control acts on the thin cake that forms on permeable rock.

Sized calcium carbonate belongs to two classes, as a weighting solid and as a bridging solid. Filtrate volume is controlled by polymers and organic materials, such as polyanionic cellulose, starch and lignite, the fluid loss control additives that act at the filter cake.

How Does LCM Bridge and Seal Fractures and Pores?#

LCM stops a loss by bridging: rigid granules lodge at the mouth of a fracture or pore throat, and finer particles, flakes and fibers then fill the gaps until the bridge seals. Losses occur in four zone types: naturally fractured formations, cavernous formations, highly permeable formations and drilling-induced fractures (Alsaba et al., AADE-14-FTCE-25, 2014). Induced fractures are opened by the mud pressure itself.

Each LCM form seals in its own way. Flaky LCM, such as mica, lies flat over an opening as a mat that smaller particles then seal. Fibrous LCM, such as cedar fiber, intertwines into a mat that bridges the opening, and smaller solids deposit on that mat until it seals. Granular LCM, such as nut shells and sized calcium carbonate, wedges into the opening as a rigid bridge.

Resilient graphite adds a fourth behavior: it deforms under load and rebounds when the pressure drops, so the seal survives pressure cycling. In a 2000 joint-industry test program, resilient graphite blended with sized calcium carbonate at 1:2 by weight raised the fracture reopening pressure, while fibers alone did not (Whitfill and Hemphill, Drilling Contractor 2004). The same authors suggest using fibers in smaller amounts than the granular materials.

Types of Lost Circulation Material Compared: Shape, Density, Dose and Status#

Granular LCM such as sized calcium carbonate, resilient graphite and ground nut shells bridge openings, flaky and fibrous LCM such as mica and cellulose fibers mat over them, and diatomaceous earth forms high-fluid-loss squeeze pills. The table below compares seven material groups by chemistry and specific gravity, type and fluid system, dose with its basis, temperature data and API 13A status.

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Doses are lb of LCM per bbl of mud (kg/m3) from the cited papers, not supplier figures; offshore status per material follows the PLONOR list.

The seven groups differ in the property that decides their use, as summarized below.

• Sized calcium carbonate: the acid-soluble granular solid, removable from a reservoir with acid.
• Graphite: resilient graphitic carbon graded by D50, used in pre-treatment and in strengthening fluids.
• Nut shells: lignocellulosic granules with no CAS number, graded fine, medium and coarse.
• Mica: flakes of a mica group mineral, graded fine, medium and coarse.
• Fibers: cellulosic, mineral and synthetic fibers; the cellulose identity applies to cellulosic fibers only.
• Diatomaceous earth: kieselguhr, the base of high-fluid-loss, high-solids squeeze pills for depleted or highly permeable zones.
• Other LCM: cellophane, cottonseed hulls, corncobs and wood from the classic lists, plus swellable polymers from the 2014 update.

Fibers and nut shells are light, so one pound of either fills more of an opening than one pound of calcium carbonate, and treatments are compared by volume in the dose section.

How Are LCM Particles Sized to the Opening?#

LCM is sized to the opening it must plug, and the Abrams rule sets the median particle size (D50) at no less than one-third of the median pore size or fracture width (Abrams, JPT 1977). Abrams also asks for at least 5 % by volume of bridging solids in the final mud. Ideal packing theory aims instead for a continuous size distribution whose cumulative volume is proportional to the square root of particle size.

Fracture rules move the target upward. Whitfill (IADC/SPE 115039, 2008) sets D50 equal to the estimated fracture width, and Alsaba et al. (2017) ask for a D50 of at least 3/10 and a D90 of at least 6/5 of the width.

The table compares the seven particle-sizing criteria by target, opening and source.

Sizing needs a continuous size distribution rather than one grade, because coarse particles bridge and finer ones seal the gaps between them. Applied to a measured pore size or an estimated fracture width, these criteria give the D50 and D90 targets that set the particle size for LCM pills and blends.

LCM Pills, Sweeps and Pre-Treatment: When Each Is Used#

An LCM pill is a batch of mud loaded with mixed LCM at high concentration and pumped after losses start, while pre-treatment keeps bridging solids in the active system before losses (Alsaba et al., AADE-14-FTCE-25, 2014). The paper calls the pill corrective and the pre-treatment preventive. A sweep is a third mode: a nominal 50 lb/bbl (143 kg/m3) LCM slug circulated through the system (Whitfill and Hemphill, Drilling Contractor 2004), and geothermal crews run sweeps before setting casing (Tuttle, Stanford Geothermal Workshop 2025).

Pill type follows loss severity. Seepage and partial losses are treated with LCM blends in the mud, severe losses with settable pills such as cement, gunk and deformable viscous cohesive plugs, and depleted or highly permeable zones with high-fluid-loss, high-solids squeeze pills (Alsaba et al. 2014). Diagnosis of the loss itself, from rate to location, belongs to lost circulation as a drilling problem.

Wellbore strengthening plugs and seals induced fractures while drilling to raise the fracture gradient and widen the operating window (Salehi and Nygaard, quoted in AADE-14-FTCE-25). The stress cage model (Alberty and McLean, SPE 90493, 2004) and the fracture closure stress model (Dupriest, SPE/IADC 92192, 2005) underpin LCM design for wellbore strengthening.

How Much LCM Does a Treatment Need?#

An LCM treatment needs 20 to 25 lb/bbl (57 to 71 kg/m3) of bridging solids in a pre-treated mud and 40 to 60 lb/bbl (114 to 171 kg/m3) or more in a pill (Whitfill and Hemphill, Drilling Contractor 2004). Every dose is a mass of LCM per bbl of mud or pill.

The table compares LCM doses by treatment, with the fluid basis and source of each row.

Bit nozzles, downhole motors and other tools set the coarse limit of a treatment. The motor row is a field record of graphite and calcium carbonate concentrations that passed through motors, not a rating of any tool.

Treatments are designed by volume, because a light material fills more of an opening per pound than a dense one. The normalization factors of the 2004 Drilling Contractor article divide each material's specific gravity by that of graphite, and the table below applies them to a 10 lb/bbl (28.5 kg/m3) graphite dose.

Calculated from the SG normalization factors of Whitfill and Hemphill (2004); treatments are sized by volume.

How to Choose LCM by Loss Zone, Fluid System and Temperature#

LCM is chosen by three conditions: loss severity, which sets the treatment type, the fluid system, which limits some fibers and squeeze pills, and hole temperature, which limits cellulosic and nut-shell LCM. Severity is graded in loss classes, and no loss classification is an API or industry standard. Seepage, partial and complete losses are the three loss classes of the 2014 classification paper, each defined by loss rate.

Five conditions narrow the choice further, each with the materials that fit it.

1. Reservoir sections that need clean-up: acid-soluble calcium carbonate, water-soluble sized salt or oil-soluble resins, the removable bridging agents of reservoir drill-in fluids.
2. Induced fractures under pressure cycling: resilient graphite with sized calcium carbonate, which keeps the seal as pressure rises and falls.
3. Oil-based and synthetic muds: some fibrous LCM have limitations in oil-based mud, and high-fluid-loss squeeze pills may underperform in non-aqueous fluids (Alsaba et al. 2014).
4. Shale and other low-permeability rock: high-fluid-loss squeeze pills are difficult to apply there (Alsaba et al. 2014).
5. Hot holes: Tuttle (2025) rates cellulosic LCM as stable below 300 degF (149 degC) as a general rule, a limit that shapes geothermal drilling fluids.

Temperature data for organic LCM come from laboratory tests. Black walnut shells soften at 360 to 500 degF (182 to 260 degC) and mixed nut shells at 380 to 480 degF (193 to 249 degC) (Loeppke 1990, cited by Lee, Stanford Geothermal Workshop 2021). Cedar fiber, cottonseed hulls, microcellulose and sawdust were degradation-tested at 194 to 482 degF (90 to 250 degC) in DOE Geothermal Data Repository submission 1660.

Graphite with sized calcium carbonate sealed fractures up to 275 degF (135 degC) at 4,000 psi (27,579 kPa) overbalance in Gulf of Mexico wells (Smith and Growcock, AADE-08-DF-HO-21). That envelope is a field record of successful sealing, not a temperature limit of graphite.

How LCM Is Tested Before It Goes Downhole#

No single test is standard industry practice for preventive LCM, while corrective LCM is tested in a permeability plugging apparatus (PPA) or an HPHT fluid-loss cell fitted with slotted, tapered or ceramic discs (Alsaba et al. 2014). Each test is judged by the 30-minute fluid loss and the time to seal.

The disc is chosen to match the opening the LCM must seal, a slot for a fracture and a permeable disc for porous rock, so the sizing criteria above carry into the test. Comparing blends on one disc at one pressure is the core of LCM evaluation in the permeability plugging test.

Offshore Discharge and Notification Status of LCM#

No discharge limit applies to an LCM as such in US offshore waters; the whole water-based mud carrying it must meet 40 CFR 435.13 and is discharged only beyond 3 mi (4.8 km) from shore. Discharged water-based mud must pass a 96-hour LC50 of at least 3 % by volume of the suspended particulate phase, show no free oil and contain no diesel oil; the section 435.13 text dates from 77 FR 29836 (2012).

In the North-East Atlantic, calcium carbonate, including marble or limestone, is on the PLONOR list (OSPAR Agreement 2013-06, Update 2026). Inorganic products such as calcium carbonate receive no CHARM color band under the Offshore Chemical Notification Scheme (OCNS) of the UK and the Netherlands, only an OCNS group from A (most hazardous) to E based on persistence, bioaccumulation and toxicity data.

The whole-mud toxicity test, the no-discharge zone near shore and the cuttings rules for non-aqueous fluids form the US offshore discharge rules of 40 CFR 435.

LCM Suppliers, Grades and Purchase Documents#

LCM is bought by material and particle-size grade, such as fine, medium and coarse nut shells or mica, or resilient graphite graded by D50, with a certificate of analysis and a safety data sheet. No API 13A grade applies to any LCM.

API Spec 13A, 19th edition (2019) with Addendum 1 (2020), Addendum 2 (2022) and Errata 1 (2024), is the current edition (API Standards Plan, checked 2026-10-27); a 20th edition is in development. Its 18th edition (2010) text lists 13 materials, and none of them is an LCM.

Grade names such as fine, medium and coarse therefore carry no common size definition, and the particle-size data on the certificate is the basis for comparing drilling fluid additive suppliers on the same material.

LCM and the Other Drilling Fluid Additive Classes#

LCM works with the other drilling fluid additive classes: fluid-loss additives control the filtrate that LCM bridges do not stop, and weighting agents set the mud density whose overbalance drives the loss.

Cement plugs and LCM in cement slurries belong to well cementing, a separate field. Fluid-loss pills in completion work belong to completion chemistry, also a separate field.

Sized calcium carbonate is also a weighting solid at low density. Its density role, next to barite and hematite, places it among the weighting agents for drilling fluids.

Rarely used and emerging LCM: swellable polymers and nanoparticles#

Classic LCM lists also include cellophane, corncobs, cotton hulls, wood, laminated plastic, shredded cane stalks and hair. These materials appear in the fibrous, flaky and granular groups of the oldest classifications.

Swellable or hydratable combinations and nanoparticles of 1 to 100 nm are the two newest categories of the 2014 classification (Alsaba et al. 2014). Nanoparticles sit at the fine end of the size range, far below the micron-sized bridging solids of the sizing rules above.

LCM in HDD, water-well and geothermal drilling#

HDD, water-well and geothermal drillers use the same LCM classes, sized to pass the pumps, valves and bit orifices of the rig. Environmental impact also weighs in the choice of LCM for HDD drilling fluids.

A water-well LCM pill is mixed to about 50 s/qt Marsh funnel viscosity (Water Well Journal). In geothermal wells, lost circulation averages about 10 % of total well cost in mature fields and exceeds 20 % of well cost in many exploration and developing fields (Saleh et al., Stanford Geothermal Workshop 2020).