Page 14 - Drilling Technology in Nontechnical Language

Chapter 1 – DRILLING GEOLOGY 5

Fig. 1–3 shows what happens when rock is compressed from the sides
until the force exceeds the rock strength. Faults (breaks in the rock layers)
develop, and part of the rock is pushed upwards. If a well is drilled across
a thrust fault, part of the rock sequence will be repeated in the well. If the
rock layers stretch, the opposite happens—normal faults develop. A well
drilled through a normal fault will have part of the rock sequence missing

(fig. 1–4).

Fig. 1–3. Thrust fault, rocks were compressed together

Fig. 1–4. Normal fault, rocks were stretched apart

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