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Shale Gas or unconventional Oil, Myths or real threats? Part I

Posté le 20/08/2013

Shale gas rigShale gas rig

 Lézin TITYConsultant Geosprojects


In France as in Europe, shale gas is seen everywhere, a kind of scarecrow which is stirred each time when a rig takes place somewhere. On one hand, there are those who denounce daily shale gas or oil as if it were a pandemic. On the other hand, there are states or politics and institutions do not make educational efforts to explain to people what it is. According to me it is only an energy source among many others. Shale gas or oil is it a threat against civilization?  It would be time that reason take place of fear.

Shale gas or oil extracted is it more harmful than conventional gas or oil? The problem to solve is the extraction technique which is hydraulic fracturing. The precautionary principle prohibiting hydraulic fracturing is normal but should be limited in time. The authorization of shale gas or shale oil is the responsibility of governments and parliaments. What is surprising is the psychosis in which we are immersed by the politicians and environment activists. Hydraulic fracturing is to blame for the groundwater pollution? What’s about seismic activity in an operation area? The truth is lacking or is elsewhere.

Do you know that there are small petroleum or gas fields a few miles from Paris? Many of these fields have been operating for 50 years in the Seine-et-Marne (Field Chaunnoy), Essonne (Vert-le-Grand, Vert-le-Petit), La Marne (Field of Trois-Fontaines), l’Aube (Field St. Martin Bosnay), Loiret (Chateaurenard), etc.

Several companies, including Total, GDF-Suez, Hess Oïl, Vermillon and others are holders of concessions or exploration permit. Global production exceeds one million tons annually. It is the same in UK, Germany, Poland, Russia, etc. Note that these licenses or concessions are for conventional oil and gas extraction with vertical or deviated or horizontal wells. Hydraulic fracturing has already been practiced in France and Europe, in onshore and offshore areas for several years to optimize production. How many cases of pollution have been recorded?

Hydrocarbons are born in great depths in buried sediments mainly clay or marl rich in organic material. Its sediments are called the source rock which has the main feature low porosity and negligible permeability. Eventually, they migrate over geological time to reservoir rocks whose characteristic is high porosity and permeability. Migration stops when the fluid reaches a structure called trap. It defines a volume in which oil accumulated in the reservoir rock, in conditions of substantial temperature and pressure. These hydrocarbons are called conventional.

Shale gas or oil is called unconventional hydrocarbons because the process of born within the source rock is the same as described above. But the hydrocarbons have not reached the reservoir, there is no accumulation. Oil or gas is trapped in the source rock. The development operations require hydraulic fracturing and are expensive.

The hydrocarbon exploration, conventional as unconventional, is done by seismic interpretation and geological data in order to map the area. A prospect or leads assessment (traps) is performed to rank them according to the potential of success. Thereafter, the wells are decided in order to confront specialists’ theories with reality. Most of the time, these well sites are vertical to achieve the objective. But it may happen that we add a deviated or horizontal to achieve other objectives or to optimize the production.


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