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Measured depth

Measured depth is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Measured depth rather than just read about it. In short: In the oil industry measured depth (commonly referred to as MD, or just the depth) is the length of the drilled borehole. In conventional vertical wells, this coincides with the true vertical depth, but in directional or horizontal wells, especially those using extended reach drilling, the two can deviate greatly.

Measured depth — main illustration
Measured depth — illustration

Key takeaways

  • Measured depth belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Measured depth to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Measured depth from memory before moving on to harder problems.

Reference excerpt

In the oil industry measured depth (commonly referred to as MD, or just the depth) is the length of the drilled borehole. In conventional vertical wells, this coincides with the true vertical depth, but in directional or horizontal wells, especially those using extended reach drilling, the two can deviate greatly. For example, at the time of writing (2012) a borehole in Odoptu field, Sakhalin-I, has the greatest measured depth of any borehole at 12,345 m, but most of this is horizontal, giving it a true vertical depth of only 1,784 m. For comparison, the Kola Superdeep Borehole has a slightly shorter measured depth at 12,262 m, but since this is a vertical borehole, this is also equal to the true vertical depth, making the Kola Superdeep Borehole deeper by a factor of 6.9.

See also Depth in a well True vertical depth Driller's depth

References

Illustrations

Measured depth: (a) is an imaginary line representing the true vertical depth, while line (b) is the borehole itself, and its length is called the measured depth.
(a) is an imaginary line representing the true vertical depth, while line (b) is the borehole itself, and its length is called the measured depth.

Worked examples

Example 1 — a first encounter with Measured depth

Start with the simplest possible case. Write down what Measured depth claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Measured depth before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Measured depth ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Measured depth

In research
Measured depth appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Measured depth in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Measured depth is common in secondary-school and first-year university syllabi. It links to neighbouring topics Petroleum engineering, Petroleum stubs, so understanding it makes those chapters shorter.
In everyday life
Look for Measured depth outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Measured depth in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Measured depth means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Measured depth out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Measured depth in simple terms?

In the oil industry measured depth (commonly referred to as MD, or just the depth) is the length of the drilled borehole. In conventional vertical wells, this coincides with the true vertical depth, but in directional or horizontal wells, especially those using extended reach drilling, the two can…

Why does Measured depth matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Measured depth?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Measured depth.

Tags

  • Petroleum engineering
  • Petroleum stubs

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