Pre-Packed Well Screens: When a Factory-Filled Screen Replaces a Gravel Pack

How dual-wall pre-packed well screens are built, how to pick glass bead size and slot, and when they replace a gravel pack in drainage and dewatering work.

By Serkan İnkaya, Mert Aytünür, Ümit Can Özer, ADEN Wedge Wire · 22 October 2026 · 14 min read

Pre-packed well screens: the short answer

A pre-packed well screen is two concentric wedge wire screens with a layer of sized filter media, usually glass or ceramic beads, filled and sealed between them in the factory. It is used where a gravel pack is hard to place or there is no room for it: narrow boreholes, drainage, recovery and dewatering wells, and re-equipping old wells.

This article covers pre-packed screens for water, drainage, remediation and dewatering wells. Oil and gas sand control pre-packs are a different product with their own qualification route and are only touched on briefly.

How a pre-packed screen is built

From outside to inside, a pre-packed section has:

• an outer continuous-slot wedge wire screen, V-wire wound on longitudinal rods and resistance welded at every crossing;
• the filter media, filled into the gap between the two screens;
• an inner wedge wire screen of the same construction;
• top and bottom end plates welded across the gap to close it, plus the end connection (weld ring, thread or other coupling).

In the published dual-screen designs both screens carry the same slot, and that slot is chosen to hold the finest bead. The media is filled with the screen standing upright and the screen is vibrated so the beads settle and leave no voids; then the ends are welded shut. Catalogue designs keep the gap between the screens at approx. 25 to 27 mm across the whole size range, from about 60 mm ID up to about 460 mm ID. A gravel pack placed on site is normally designed 50 to 125 mm thick, approx. 75 mm being the usual optimum.

Flow is outside to inside. Water passes the outer slot, the bead layer, then the inner slot, and the pump sits in the bore of the inner screen. Because the outer V-wire slot widens inwards, a grain that gets through the slot does not wedge in it.

Pre-pack or gravel pack: the main differences

So the pre-pack filter is thinner but very uniform, and since it is never placed in the hole it cannot segregate or bridge during placement. With a gravel pack you get more filter thickness and can correct it later, but it needs annular space and good placement practice to work.

When a pre-packed screen makes sense

We see pre-packs specified mostly in these situations:

1. The borehole is too small for a proper pack. If the annulus cannot give the approx. 75 mm design thickness, a pre-pack puts a defined filter on the screen anyway.
2. Placing gravel is difficult or unreliable, for example in a deep, narrow hole, in a collapsing formation, or where the drilling method leaves no clean annulus.
3. Drainage and recovery wells where the contractor wants a fast installation without a separate packing step.
4. Horizontal or inclined drains, where a pumped gravel pack is hard to place evenly around the screen.
5. Re-equipping an existing well, where a smaller screen is set inside the old casing and there is no way to pack between them.

Published catalogue data also give the dual-screen construction a higher collapse rating than a single screen of the same size. That is plausible, since two welded screens and a compacted bead layer carry load together, but any collapse value for a specific screen must come from a project calculation. We do not quote collapse figures without one.

Before choosing one, weigh the limits:

• The filter is thin. If the aquifer grading is wide or the well is pumped hard, a 25 mm bead layer has less reserve than a 75 mm gravel pack.
• If the bead layer clogs from fines, iron or biofouling, it cannot be washed out or replaced in place. The section has to be pulled.
• A pre-pack is several times heavier per metre than a single screen of similar size, and it takes more material and much more labour to build. Expect a higher price per metre.
• The borehole still has to pass the largest OD, which is usually the coupling, not the screen body.

Choosing the fill: glass beads, ceramic or sand

Glass beads are the common fill for water and drainage work. They are round and very uniform, with a uniformity coefficient (D60 / D10) of approx. 1.5 against approx. 2.5 for a good graded gravel pack. A uniform fill has a narrow band of pore sizes, so the slot can be matched to it closely. Ceramic beads are also used, and some catalogue pre-packs use resin-free ceramic media, which is less inclined to biofilm and scaling than resin-bonded fills.

Bead size is chosen in the same way as gravel pack size, from the sieve analysis of the finest aquifer layer the screen faces:

1. Take the D30 of the aquifer, the size that 30 % of the sample passes.
2. Multiply it by a pack-to-aquifer ratio. Published guidance differs: the US NRCS National Engineering Handbook gives 4 to 9, a widely used water well design text gives 3 to 8, and one manufacturer works with 4 to 6. Lower ratios suit fine, uniform sands; higher ratios suit coarse or poorly sorted ones.
3. Pick a bead band whose D30 falls in that range.
4. Choose the slot so it holds the finest bead in the band.

Full method, with the gravel pack case worked through: slot and gravel pack selection.

Choosing the slot

With glass beads the slot has to retain all of the media, not 90 % of it as with gravel. One published catalogue pairs standard bead bands with slots as below (converted from inches, rounded).

In every row the smallest bead is clearly larger than the slot, roughly 1.1 to 1.6 times. As an illustration: an aquifer with D30 of 0.35 mm and Cu of 2.2 is a fine, uniform sand. At a ratio of 4 to 6 the pack D30 should be 1.4 to 2.1 mm. A 1.5 to 2.0 mm bead band sits in that range, and a 1.0 mm slot holds all of it. One drainage well enquiry we worked on this year asked for exactly that pairing, 1.0 mm slot with 1.5 to 2.0 mm beads; another asked for a 2.75 mm slot with 3.5 to 4.0 mm beads, which follows the same rule. This is an illustration, the real design starts from your own sieve curve.

Open area is the second check. For wedge wire it is s / (s + w) x 100, where s is the slot and w the top width of the wire. On the same slot the outer screen of a pre-pack often ends up with less open area than the inner one, so we check entrance velocity on the outer screen, normally against 3 cm/s. You can try wire and slot combinations with our Open Area Calculator.

Drainage, recovery and remediation wells

Drainage wells in fuel storage areas, tank farm bunds and recovery wells on contaminated sites are where pre-packs earn their place most often, and the same questions come up every time.

Pick the stainless grade from the water analysis, chloride first. Nickel Institute guidance for neutral pH at ambient temperature puts the chloride limit at approx. 200 ppm for 304, 1,000 ppm for 316 and 3,600 ppm for duplex 2205. Tell us if the water carries hydrocarbons, solvents or other contaminants, so we can review the metal and any non-metallic parts in the casing and screen column for that service. More on grades in our article on stainless steel well screens and on our Materials page.

A stainless screen joined directly to carbon steel casing in saturated ground sets up galvanic corrosion of the carbon steel. Use a dielectric (insulating) coupling between them, or at least plan for it.

The ID of the inner screen is set by the pump, sensor or skimmer that has to go inside, with clearance. Keep the upward velocity inside the screen at or below approx. 1.5 m/s.

A 6 m section does not fit in a 20 ft container (internal length 5.898 m). For crated sea freight we keep net lengths in a 20 ft box to approx. 5.7 m, and longer sections go in 40 ft containers. If you want a single-piece screen, say so early, because it decides both the build and the freight.

Horizontal remediation wells under tank farms have been completed with stainless steel screens. Wire-wrapped screen bodies are designed to hang in tension, not to be pushed under axial compression, so a horizontal pull-in needs the load path through the rods and joints checked. In oil and gas, thin pre-packs for horizontal wells are offered with a heavier outer wire for short-radius wells and an optional perforated protective shroud against damage while running in, and with a recommended minimum annular clearance of approx. 0.75 in (19 mm). The same caution applies to long horizontal drains.

Dewatering wells

Dewatering wells are temporary, but the screen still sees fines from the formation, and a pre-pack saves the time of placing a pack in each hole. If the screens are to be pulled and reused on the next site, tell us at enquiry stage. Pulling puts the full column weight on the longitudinal rods and the couplings, so tensile capacity, which comes from the number and size of the rods, matters more than in a permanent well.

Standards

For water wells, the current German standard for wire-wrapped well screens is DIN 4900-2:2017; DIN 4935, which older specifications still quote, was withdrawn in 2017. We make pre-packed screens to customer drawing and specification, and material certificates (EN 10204 type 3.1) are supplied with the screens. Sand control pre-packs for oil and gas completions are qualified under ISO 17824 / API Spec 19SS; that is a separate product route and not what this article describes.

What to send us for a pre-packed screen quote

• sieve analysis of the aquifer or formation, at least of the finest layer the screen will face;
• borehole diameter and well depth, and the depth range of the screen section;
• required inner diameter, or the pump or sensor that has to fit inside;
• screen length, number of sections and the longest single piece you can handle;
• water analysis: pH, chloride, H2S, iron, and whether hydrocarbons or other contaminants are present;
• casing material and connection type (weld ring, thread, flange), and whether the well is vertical, inclined or horizontal;
• expected flow rate, and whether the screens will be pulled and reused.

If you already have a catalogue reference or a drawing from another supplier, send it as well. We work from the dimensions, slot and bead band, not the product name. See also Water Well Screen and the overview of screen types in Water Well Screen Types Compared.

Send us your data

ADEN Wedge Wire is a wedge wire screen manufacturer based in Istanbul, Turkey, with a European office in Sindelfingen, Germany. Send the grain size curve, the borehole diameter and the pump you plan to use. We reply within 24 hours and follow up with a proposal that includes the bead size and slot. Use the RFQ form or email info@adenwedgewire.com.

Frequently asked questions

References

1. National Engineering Handbook, Part 631, Chapter 32, Well Design and Spring Development, USDA Natural Resources Conservation Service
2. Chloride guidance for stainless steels, Nickel Institute
3. DIN 4900-2:2017, Brunnenfilter aus nichtrostendem Stahl, DIN
4. EN 10204:2004, Metallic products, types of inspection documents, CEN
5. ISO 668, Series 1 freight containers, ISO