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What is fracking?

Fracking is, basically, the creation of fissures in targeted rock formations deep underground. An emulsion, or mixture, of water, sand and chemical agents is pumped into the target formation.

The chemical agents keep the sand in suspension in the fluid throughout the pumping process. When the chemical agents break down the fluids are removed and the sand remains to keep the fissures open and increase the flow characteristics of the rock.

The chemicals used in modern fracking pose no threat to the environment. More on chemical additives here

Why is fracking done?

Fracking is mainly carried out in natural gas reservoirs, and coal-seam gas (CSG) bearing coal seams, to encourage the gas to flow more freely; and thereby increase the rate of well and field recovery, and the total amount of gas recovered. In some cases, fracking can reduce the number of wells needed to extract a resource and, less frequently, fracking has been used in oil reservoirs.

Fracking is only done if economically viable. In the case of CSG, fracking of a coal seam is often necessary for encouraging the gas to flow at economic rates of extraction.

As the more easily-tapped sources of oil and gas are extracted, and as the price of petroleum rises, the world is likely to see increased use of "unconventional technologies", including fracking.

The geology

Two aspects to gas-bearing rock strata must be understood to complete the picture on why fracking is done: porosity, the amount of pore space within the rock, and permeability, the degree to which the pores are inter-connected.

To illustrate, pumice floats because there are many empty spaces within the rock but the spaces are not connected to one another – this rock is said to be highly porous but not permeable. Imagine, on the other hand, a cone of oranges stacked high in a grocer’s shop. If you pour water over the stack, it will flow easily through the oranges onto the shelf; the stack is both porous and permeable.

Some gas-bearing strata are in between. The spaces in the rock are very small and are full of gas but the gas cannot move easily on its own, even from an area of high pressure (deeply-buried rock), to low pressure (the well). By opening fissures in this rock, fracking greatly increases the permeability of the reservoir.