Conductance and Open Area in VSM300 Primary Deck Screens
Introduction: Conductance and open area describe two different things on a VSM300 primary deck, and treating them as one number is what leads operators to the wrong screen choice.
Walk up to a shaker and the question is almost always the same: will this screen handle the mud coming at it? Two screens can carry the same mesh number, look nearly identical on the rack, and still behave differently once the deck is running. That gap is where most confusion starts, because open area is a measurement of geometry and conductance is a statement about flow capacity. Keeping the two apart helps operators read screen labels more accurately, interpret what a VSM300 shaker screen supplier is actually offering, and judge field results without blaming the mesh for everything.
Why Conductance and Open Area Are Often Confused on the Shaker Deck
Most of the confusion is verbal. On a shaker deck, people use "open" as shorthand for "mud is going through it," and that habit quietly folds two separate measurements into one idea. A screen that drains well gets described as having high open area, and a deck that floods gets blamed on low open area, even when the mesh and the frame are doing exactly what they were built to do. Spec sheets make it worse, because mesh count, API designation, open area, and conductance usually sit side by side in the same column, which reinforces the impression that they are interchangeable views of one property. The two terms do tend to move in the same direction, and that pattern is what makes the mix-up stick. A cloth with more unbonded surface generally does pass fluid more easily, so operators see a rough correlation and stop questioning it. But conductance is a flow capacity figure produced under defined conditions: a specific fluid, a specific oscillation, a specific test setup. Field mud is not a defined fluid. Solids load, viscosity, clay chemistry, and particle shape all shift from one well section to the next, and each one changes how quickly fluid clears the screen. Cut point is a third label with a third job, describing the particle size at which separation happens, so conductance, open area, and cut point are three separate statements rather than three names for one number.
How Open Area Describes Geometry While Conductance Describes Flow Capacity
The split gets easier once each term is tied to the question it actually answers: how much metal is missing, and how much fluid moves. A working breakdown looks like this.
- Geometric open area. Open area counts the surface you can see through. It takes the apertures across the mesh, multiplies them by their individual size, and compares that total against the full screen footprint, subtracting wire diameter and any blanked frame or support area. It is a static, geometry-only figure, so the same screen returns the same open area whether it sits on a pallet or is clamped onto a deck.
- Conductance under vibration. Conductance answers a flow question instead of a geometry question. In oilfield terminology it is treated as a flow capacity concept, describing how much fluid a screen passes under stated test conditions, including the fluid used, the oscillation applied, and how long the measurement runs. Two screens with matching open area can still post different conductance values when weave, mesh layer count, or surface profile differ, because those details change how fluid drains through the cloth.
- Field throughput factors. Field throughput is the number operators watch on the pit, and it is the product of the screen plus everything around it. Mud viscosity, solids concentration, drilled-solids shape, reactive clays, deck angle, g-force, and how evenly flow is spread across the deck all push throughput up or down. Blinding, where particles wedge into apertures, can cut flow on a screen whose measured open area never changed at all.
The practical effect is that open area and conductance describe different parts of one story, and neither alone predicts what a deck will do with a given mud. A screen with generous open area can blind quickly in sticky clay, while a tighter screen with cleaner drainage can pass more fluid at the same pump rate. That is why field results sometimes contradict what a spec sheet seems to promise, and why comparing screens on a single number rarely settles an argument between two experienced hands.
What the 890 by 686 by 73 mm Format Tells You About the VSM300 Primary Deck
The 890 mm × 686 mm × 73 mm format is a fit statement. Length and width define the footprint that drops into the VSM300 primary deck seat, while the 73 mm figure describes the frame height profile that has to clear the support rails and sit correctly in the clamping arrangement. PRM Drilling lists VSM300 primary deck replacement screens at those dimensions, built with corrugated pre-tensioned mesh bonded to a one-piece laser-cut steel sheet frame with cross support, and rated for use with both water-based and oil-based mud systems. For anyone sourcing a replacement, the numbers answer the first question on the list: will it mount. They do not describe throughput, and they are not a performance rating. Two screens can share the same 890 × 686 × 73 mm envelope and still differ in mesh count, wire diameter, weave, and number of layers, and those differences change both separation and flow. What the format does tell an operator is that the screen was made for this deck rather than adapted to it. The frame edges line up with the clamp, the corrugated profile keeps the mesh under pre-tension instead of letting it flex, and a one-piece sheet frame removes the welded joints that tend to open up under continuous vibration. Those are construction facts that support consistent fit and service life. The format also sets up the right comparison questions. Once mounting is settled, the useful conversation turns to mesh designation, measured open area, and any conductance figure the shaker screen manufacturer publishes, ideally on the same test basis so the numbers can be placed side by side. Operators comparing two candidates, and buyers assembling wholesale shaker screens orders for a rig, get more from a consistent specification sheet than from a single headline number. Anyone evaluating a primary screen supplier can ask which figures come from a stated test method and which are simply descriptive.
Conclusion
Conductance and open area both matter on a VSM300 primary deck, but they answer different questions. Open area measures geometry: how much of the screen surface is actually open. Conductance describes flow capacity under defined conditions, with a stated fluid and a stated motion. Field throughput is a third thing entirely, shaped by mud properties, solids load, blinding, and how the deck is run. Once an operator separates those three, screen labels stop blurring together. For a replacement on a VSM300 primary deck, start with the 890 × 686 × 73 mm fit and the frame construction, then compare mesh, measured open area, and conductance on a common basis before deciding which screen belongs on the deck.
FAQ
Q：What is the difference between conductance and open area in shaker screens?
A：Open area is a geometric figure, the percentage of screen surface that is not blocked by wire, frame, or support structure. Conductance is a flow capacity concept, describing how much fluid a screen passes under stated test conditions that include the fluid and the oscillation used. Because one is measured on static cloth and the other reflects fluid movement, the two can point in different directions on the same screen.
Q：Does more open area always mean better VSM300 primary deck performance?
A：No. More open area gives fluid more places to pass, but performance on the deck depends on mud viscosity, solids concentration, particle shape, deck motion, and blinding. A screen with high open area can blind quickly in sticky clay, and a screen with less open area can drain better when the flow path stays clear. Open area is one input, not a performance promise.
Q：Why does the 890 x 686 x 73 mm size matter for VSM300 primary deck screens?
A：Those three numbers describe fit and format. Length and width match the primary deck seat, and the 73 mm height profile lines up with the support rails and clamping arrangement so the screen mounts properly. The dimensions confirm installation compatibility; they say nothing about mesh count, separation size, or how much mud the deck will process.
Sources / References
conductance (Energy Glossary, SLB)
cut point (Energy Glossary, SLB)
Standards (American Petroleum Institute)
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