Page 55 - Petrophysics

CHAPTER 2

INTRODUCTION TO

PETROLEUM

GEOLOGY

REVIEW OF COMPOSITION OF THE GLOBE

Geology is the study of the earth, which is a dynamic system covered by
crustal plates that are constantly moving and changing in structure. The
crustal plates are driven by deeplying forces that are not yet completely
understood. New crustal plates are being formed by magma rising from
molten regions deep in the earth at mid-ocean rifts. Other crustal plates
are being consumed as they are drawn downward into the mantle at
subduction zones at the edges of some continents, such as the Pacific
coasts of North and South America.
Detailed analyses of earthquake wave seismograms, waves that travel
on the earth’s surface, gravity and magnetic differences, heat flow from
the interior, and electrical conductivity have been used to develop a
composite picture of the globe. Four distinct zones have been identified:

(1) the lithosphere, which includes the continental and ocean crusts;
(2) the mantle underlying the lithosphere, which is readily recognized
because the seismic (earthquake) waves increase in velocity at the
boundary known as the Mohorovicic discontinuity in honor of its
discoverer (generally called the Moho discontinuity);
(3) a liquid outer core composed principally of nickel and iron; and
(4) the solid inner core.

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