Page 10 - Drilling Technology in Nontechnical Language

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DRILLING GEOLOGY

Overview

This chapter will examine geology as it relates to drilling operations.
It is necessary to understand something about the physical and chemical
characteristics of rocks in order to understand drilling processes
and problems. The chapter also describes the basic principles of

hydrostatic pressure exerted by a fluid at depth, as this is important for
drilling operations.
This brief chapter will cover some important concepts that should be
understood for the chapters that follow.

Origins of Rock

When the earth first formed, it consisted of molten rock. As the surface

of the planet cooled down, the planet surface solidified. Rocks formed by

molten rock cooling and solidifying are called igneous rocks. Basalt and
granite are examples of igneous rock (fig. 1–1).

Water and gases form the oceans and atmosphere. The gravitational
pull of the sun and moon and solar heating cause movements of the
atmosphere (weather) and the oceans (tides and currents). The movements
of air, water, and ice erode rocks, releasing rock particles. These effects are
called weathering.
Particles of rock, from tiny grains to huge boulders, can be carried
long distances by wind and water. Eventually the forces carrying the rock
particles are reduced, and the rock fragments fall to the earth’s surface,
or to the bottom of a water body, forming thick beds of material called
sediments. As the water or wind slows down, the largest fragments are

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