Fracture development and fluid transport

Permeability is a measure of how easily fluid flows through the rock. In porous media, the permeability is determined by the interconnection of pores. In solid rock, the porosity is normally quite low, due to diagenesis processes such as compaction and cementation, so that the fluid transport mainly takes place through interconnected fractures.

The term 'rock fracture' refers to any significant mechanical break in the rock. Fractures are the most common structures in the brittle part of the lithosphere. The generation and mainentance of fracture-generated permeability depends on (1) the formation of extension fractures and (2) the formation of shear fractures.

In fractured reservoirs, such as this carbonate reservoir analogue at Nash point, Wales (UK), the reservoir permeability is determined by the fractures that cross through several layers (non-stratabound fractures).

Numerical modelling

To understand the mechanisms behind fracture propagation and arrest, the linking up of fractures, and how fracture aperture changes with fracture evolution we need numerical modelling.

A numerical model showing a hydrofracture propagating in a layered and faulted rock.

Applications

The conditions for fracture development in relation to crustal fluid pressure and transport have implications for many fields, such as:

• Petroleum production and exploration
• Subsurface storage of carbondioxide
• Geothermal exploration
• Volcanic risk assessment
• Groundwater supply
• Nuclear waste disposal