Page 83 - Introduction to Petroleum Engineering

4

PROPERTIES OF RESERVOIR ROCK

Porosity and permeability are fundamental rock properties. Porosity is a measure of
the storage capacity of the rock and permeability is a measure of rock flow capacity.
Storage capacity tells us how much resource can be contained in the rock, and flow
capacity tells us how fast we can produce the resource. Porosity, permeability, and
associated topics are the subject of this chapter.

4.1 POROSITY
Consider a handful of sand that contains sand grains and space between grains.
The volume of the sand is the sum of the volume of the sand grains plus the volume
of space between grains. Figure 4.1 presents a sketch of a block of rock with grains
of sand filling the block and an example of Berea sandstone from Berea, Ohio. The
Berea sandstone image is a microscopic view of sandstone surface that has been
expanded 25 times. Rock grains and the space between grains, called pore space, are
visible in the image.
What is the difference between a handful of sand and a piece of sandstone?
The handful of sand consists of loose grains of sand. By contrast, grains in the sand-
stone are cemented together by minerals that have precipitated from the mineral‐rich
water that has occupied the pore space over tens of thousands, perhaps millions, of
years. Furthermore, sandstone is typically composed of a variety of grain sizes.
Small grains can fill pore space between larger grains and reduce the porosity

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