Page 11 - Drilling Technology in Nontechnical Language

2 Drilling Technology in Nontechnical Language Second Edition

deposited first. Smaller fragments (being more easily carried) would move

further. In this way, the rock fragments could become sorted so that a
particular bed of sediment might consist of fragments all of a similar
size. Large particles are deposited in high-energy environments (e.g.,

a fast-flowing river), and small particles are deposited in low-energy
environments (e.g., a lake or swamp).

Fig. 1–1. Earth’s structure

Over millions of years, these sediments became buried deep within
the earth, subjected to high pressures (from the weight of rock above them)
and temperatures (the earth gets hotter at increasing depths). The minerals
in the sediments change chemically, forming rock. This process of forming
new rock by chemical changes to sediments is called diagenesis. Other
types of rock form by small grains of mineral becoming bonded together
by minerals growing where the grains touch, such as sandstone. This
process is called cementation.
Rocks that are formed by the diagenesis or cementation of sediments
are called sedimentary rocks. Sandstone is one type of sedimentary rock.
Existing rocks of any type can be physically changed by high pressures
and temperatures. This process is called metamorphosis (the same word

that applies to a caterpillar changing to a butterfly). These changed rocks
are called metamorphic rocks.

The rock cycle diagram (fig. 1–2) was first constructed by Scottish
geologist James Hutton in a book published in 1795, The Theory of the

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