文档介绍：Chapter 1 Subsurface Macro Structure
The flow of fluids and transport of species through porous media occur in a
macroscopic system with geometric boundaries and internal structure. When the
system is subsurface formations of the earth, it is described by the structural
geology of the system. Even though the geology presented here will be
superficial, it will provide the setting for a more detailed study of the transport
processes.
Depositional Environments
The formations making up the earth’s crust is described by the term “facies”.
This is an interpretative description that has many levels. Most everyone is
familiar with the meaning of igneous, metamorphic, and sedimentary facies. The
sedimentary facies is of most interest with respect to fluid flow. The sedimentary
facies is broadly divided into sandy or sandstone facies, shaly facies, and
carbonate facies. The sandstone facies can be divided into “deep water facies”,
“turbidite facies”, “deltaic facies”, etc. As you can see, the facies is related to the
environment in which the sediment was deposited. Figure is a
representation of the various environments that sediments may be deposited.
Fig Schematic representation of sedimentary environments
(from Bjorlykke, 1989)
1-1
Fundamental Mechanism for Grain Size Sorting
The most noticeable difference in sandstones is the size of the grains
making up the rock. The sorting mechanism in water borne sediments is based
on Stoke's Law (for small particles). Consider the balance of forces acting on a
spherical particle with radius R settling in a fluid by the action of gravity. There is
the buoyancy force and the drag force as a result of its motion. The velocity of
settling can be determined be equating these two forces.
4
FRg=∆π 3 ρ
buoyance 3
= πµ
FRvdrag 6
2
vRg=∆2 µρ
9
Thus larger particles settle faster than smaller particles in proportion the square
of the particle size