Open hole vs cased hole logging is one of the most common formation-evaluation searches on oilfield sites — and one of the easiest to answer with a dictionary sentence that does not help procurement. Buyers usually need three things: when each path is used, what changes after casing and cement are in place, and which fields to put in an RFQ so a logging conversation is actionable.
CNPS supplies oilfield equipment and logging-related solutions. This article feeds the existing comparison page and the logging / MWD / LWD hubs — it does not invent tool ratings or replace a well program.
Start with the borehole state, not the acronym
| State | What the tool “sees” | Typical timing |
|---|---|---|
| Open hole | Bare formation wall (and borehole fluid) | After drilling a section, before casing that interval |
| Cased hole | Formation behind steel casing and usually a cement sheath | After casing / cementing, during completion, workover, or production diagnostics |
If your RFQ only says “need logging,” vendors cannot tell whether you are evaluating an open interval or a completed string. Write the borehole state first.
For a shorter primer already on the site, see What’s the difference between open hole and cased hole logging?.
Open-hole logging: evaluate the formation before you pipe it
Open-hole logging runs tools in an uncased interval so sensors couple more directly to the formation. That is why many petrophysical suites (resistivity, porosity, density, acoustic, imaging — depending on the program) are planned in open hole.
Buyer language that belongs in the RFQ
- Hole size / bit size and expected washout risk.
- Mud type and weight (or clear fluid) — borehole environment drives tool choice.
- Interval tops/bottoms and the decision the log must support (landing, completion design, reserves conversation).
- Conveyance preference: wireline, pipe-conveyed, or while-drilling alternatives when hole conditions are unstable.
Open hole is not “always better.” Hole instability, differential sticking, and schedule pressure often push teams to case earlier and accept cased-hole constraints.
Cased-hole logging: look through pipe — on purpose
Cased-hole logging evaluates the well after casing (and typically cement) is in place. Tools must work through steel and cement, so the measurement physics and the questions change: cement evaluation, corrosion / metal loss, saturation behind pipe, production profiling, and intervention diagnostics are common themes.
Buyer language that belongs in the RFQ
- Casing size, weight, and grade (as project data).
- Cemented vs partially cemented assumptions.
- Well status: newly completed, producing, shut-in, workover.
- Pressure-control needs (lubricator / well control) if the well is live.
- The decision: integrity, bypassed pay, water contact, or production allocation.
Cased hole is not a failed open-hole plan. It is often the correct path when the well is already piped or when the question is about the completion, not the virgin borehole.
Open hole vs cased hole: a practical comparison
| Topic | Open hole | Cased hole |
|---|---|---|
| Access to formation | Direct (borehole wall) | Through casing ± cement |
| Typical questions | Lithology, porosity, saturation, borehole geometry | Cement / integrity, behind-pipe fluids, production diagnostics |
| Schedule risk | Hole condition and trip time | Well control and access through completion |
| Common RFQ failure | No mud / hole-size data | No casing / cement / well-status data |
| Related CNPS hubs | Formation evaluation conversation → logging pages | Same hubs + completion / integrity context |
Where mud logging, LWD, and MWD fit
Do not collapse every “logging” search into wireline open vs cased:
- Mud logging watches cuttings, gas, and drilling signals while the well is being drilled.
- LWD acquires formation measurements while drilling — often when open-hole wireline risk is high.
- MWD tools support directional and drilling measurements; they are adjacent to, not identical with, formation-evaluation wireline.
A clean RFQ states which of these jobs you actually need.
RFQ checklist (minimum)
- Open hole, cased hole, or both (by interval).
- Hole size / casing size and weight.
- Fluid / mud system and well status (drilling, completed, producing).
- Interval and the decision the data must support.
- Conveyance and well-control constraints.
- Deliverables expected (curves, images, cement map, production log — as project needs).
- Business email and a technical contact.
Then request a quote.
FAQ
Is cased-hole logging only for old wells? No. New wells are logged in cased hole for cement and completion diagnostics as well.
Can one toolstring replace the other? Not honestly. Physics and questions differ. Spec the borehole state.
Does this article list CNPS tool model numbers? No. It feeds the logging conversation and quote path without inventing SKUs.
Where should I start on cnps.com? Start with the open vs cased comparison, then mud logging / LWD / MWD hubs as needed, then the quote form.
Next step
Send the borehole state and interval data — not a generic “need logging” line.
