Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 417

well

0

water table

1

formation will
fracture

2

no
injection

injection will
occur

0 50 100
Pressure (Mpa)

Figure 9.6.3 Pressure profi les relevant to fl uid injection
Sketch of various pressure profi les in the subsurface relevant to fl uid injection. The
water table, which is defi ned as the level of water in an open static well at equilibrium,
is the starting point of a hydrostatic pressure profi le.

Question 9.6.1 Fracture permeability

Examples of fractures in a cave carved into
soft chalk (calcium carbonate) are shown
in the fi gure. These fractures were proba-
bly caused by near-surface subsidence or
stress changes related to the excavation of
the cave. If there is on average one fracture
every 2 m with aperture 0.5 mm running
through this otherwise low-permeability
rock, what is the effective permeability of
the rock? Hint: The correct answer gives a
permeability similar to that of clean
sandstone.
Fractures exposed in a cave impart a
large overall permeability to an otherwise
low-permeability rock. Photo by Curt
Oldenburg, 2011.