Pick a shaker screen by “mesh” alone and you are guessing. Mesh count never described what a screen actually does to the fluid, and two screens with the same mesh from different makers could perform completely differently. API RP 13C exists precisely so you no longer have to guess — it gives every screen a label that means the same thing across every manufacturer.
What the API RP 13C label tells you
The standard — a revision of the older API RP 13E, and internationally ISO 13501 — defines a screen by measured properties, tested the same way industry-wide, so a screen from one maker is genuinely comparable to one from another:
- Separation cut (D100 / cut point) — the particle size, in microns, at which the screen splits the feed (100% of larger particles retained). This decides how fine a solid you remove, and the designation is set by matching the cut to the nearest ASTM sieve.
- Conductance (kD/mm) — how freely fluid passes through the screen. This decides how much fluid the screen can handle before it floods.
- Non-blanked open area — how much of the panel is actually working surface.
Both cut point and conductance are required on the permanent screen label — something raw mesh count could never deliver.
The trade-off you are always managing
Cut point and conductance pull against each other. A finer cut removes more solids but passes less fluid, so it floods sooner. A coarser cut handles more fluid but lets finer solids through to the next stage. Screen selection is simply choosing where on that trade-off your section needs to sit.
| Section | Choose | Why |
|---|---|---|
| Top-hole, high ROP | Coarser cut, higher conductance | Handle the heavy fluid load and large-volume returns without flooding. |
| Reservoir / lower sections | Finer cut | Protect mud properties and remove fine drilled solids, accepting lower throughput. |
| Weighted mud | Watch cut vs barite size | Too fine a screen starts removing the weight material you paid for. |
Reading the deck by eye
The label gets you the right screen; the deck tells you whether it is working. The single most useful thing to watch is the fluid pool — the “beach”:
- A small pool that breaks well before the discharge end — healthy. The screen is handling the load with margin to spare.
- Fluid running off the end of the screen — you have out-run its conductance. The screen is too fine or the load too high, and you are losing whole mud over the back.
- A screen nearly dry across its whole length — you can likely afford to go finer and remove more solids.
Blinding, holing and the things that fool you
Two failure modes quietly wreck cut point regardless of label:
- Blinding — near-size particles plugging the openings (common in sticky or fine formations). It cuts conductance and floods a correctly chosen screen.
- Holing — a torn or punctured panel lets un-screened fluid bypass entirely. A single small hole can undo the whole deck, because fluid takes the path of least resistance.
Walk the screens, look for shiny worn spots and tears, and replace panels as a set — a fresh screen beside a worn one just unloads onto the old one.
Key takeaways
Read the label, match the section, watch the deck. The API RP 13C cut point and conductance turn screen selection from folklore into a decision you can defend; the fluid pool turns the running shaker into a live readout of whether that decision was right. That is screen selection without guesswork.