Natural gas is located deep below the earth's surface in the pores of deposits. To increase the flow from these deposits, drillings are hydraulically stimulated.
For “hydraulic fracturing” (or “fracking" for short) liquid is pressed into the rock, at selectively chosen depths, under high pressure and at a high rate of flow. This gives rise to thin cracks. To prevent these cracks from closing again, very strong and small balls of bauxite are also pressed into the cracks with the liquid, to hold them open. This ensures, for the oil and gas, that the paths of flow to the well are now enlarged so that the natural gas can be extracted from the deposit more efficiently.
Benefits of the Technology
- Fewer drillings are needed to reach the raw materials of a reservoir. This reduces impact on the environment.
- Production at high rates of flow is possible over a longer period.
- The quantity of produced hydrocarbons per drilling increases.
Planning and Preparations for the Work
The aim of each fracturing process is to increase the delivery rate with as little liquid and propping agent as possible. For this reason the entire process is precisely planned and simulated. Once planning is completedan operating programmme is prepared for checking by the mining authority.
The operating programme must first be approved by the mining authority before the necessary material and personnel can be sought and the work begun.
Sole Use of Non-Poisonous and Non-Environmentally-Harmful Liquids
As a carrier for the propping agent the pumped liquid is composed of:
- water (95 %)
- additives (5 %)
For fracking only licenced, non-poisonous materials are used. The components of the "frac fluids" are continuously analysed and improved.
The propping agent is bauxite, which is a highly pressure-resistant ceramic product. It is non-toxic. After the work the fluid and part of the propping agent are returned to the surface and then disposed of by companies professionally certified for this purpose. For all waste there is a special plan of operations that is approved by the mining authority. The rest of the propping agent remains in the direct fracking area where it holds the cracks open.
Fracking in Conventional Natural Gas Reservoirs
The reservoirs lie in the very small pores of geological sandstone formations at depths of around 4,700 to 5,200 metres. The fracturing process used by DEA in these conventional reservoirs in the past have had no negative effects.
In Germany no single case is known in which fracking activities have led to pollution of the groundwater or to mechanical consequences on the site surface.
Conventional and Unconventional Natural Gas Production in Comparison
Conventional reservoirs are located at a great depth of approx. 4,000 to 5,500 metres. Unconventional deposits in Germany are located at a depth of approx. 1,000 metres. One of the most important differences lies in the fact that the natural gas in conventional reservoirs can already flow, whereas in unconventional reservoirs it has to be forced to flow via fracking activities.
In general it can be said that it is not the natural gas (methane) that is conventional or unconventional but the reservoir in which it can be found. Conventional reservoirs have to do with condensed sandstone from which the so-called "tight gas" is produced. Sandstone, in contrast to the shale in unconventional reservoirs, is more porous and thus more permeable for the natural gas. To recover the so-called shale gas from the shale of unconventional reservoirs, flow channels must be created by fracking activities.
|Conventional Gas Reservoirs||Unconventional Gas Reservoirs|
|Natural gas in sandstone or limestone layers. In Germany only in very deep-lying earth layers around 4,000 to 5,500 metres.||Natural gas in coal-containing layers or in clay. In Germany as from 1,000 metres.|
|The natural gas has collected in a trap-like structure with mighty gas-and-liquid-retarding top layers through which contact with the groundwater is not possible.||In both cases the layers can be very close to the surface (in the United States, for example, as from a depth of 100 metres) and sometimes have no top layer.|
The natural gas can flow alone to the well.
|The natural gas cannot flow alone to the well (fracking is necessary).|
Fracking activitiesrequire the pumping of around 300 m³ to 400 m³ of liquid into the well.
|Fracking activities require the pumping of around 20,000 m³ of liquid into the bore hole.|