Page 115 - Introduction to Petroleum Engineering

6

PETROLEUM GEOLOGY

The ability to manage subsurface resources depends in part on our knowledge of the
formation and evolution of the Earth. We describe the geologic history and structure
of the Earth and then present concepts from petroleum geology.

6.1 GEOLOGIC HISTORY OF THE EARTH

The age of the Earth is approximately 4.5 billion years old based on radioactive
dating of the oldest available rock samples. The cross section of the Earth’s interior
is subdivided into an inner core, the mantle, and the crust (Figure 6.1). Seismic mea-
surements have shown that the core consists of a crystalline inner core and a molten
outer core. The electric and magnetic properties of the Earth and the density of the
core provide evidence for identifying the metal as an alloy of iron and nickel. Iron is
the dominant constituent.
The density of rock in the mantle is greater than in the crust because the mantle
contains primarily basalt, a dark volcanic rock. Basalt is composed of magnesium
and iron silicates. Basalt at the surface of the mantle exists in a semimolten state.
This layer of semimolten basalt is called the asthenosphere. As we descend through
the mantle, the rigidity of the basalt increases until the mantle acquires a rigidity in
excess of the rigidity of steel.

Introduction to Petroleum Engineering, First Edition. John R. Fanchi and Richard L. Christiansen.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/Fanchi/IntroPetroleumEngineering