Hydrocarbon source-rock

In recent years, the development of bedrock hydrocarbon production (shale oil and gas) has considerably altered the US energy landscape.

Bedrock hydrocarbons are liquid or gaseous hydrocarbons that have remained trapped in the organic-rich clay layer (the bedrock), where they were formed by pressure and temperature increases during their burial over geological time. Some of the hydrocarbons formed in the bedrock are expelled, and, if geological conditions are favorable, will go on to form conventional deposits. The remainder is bedrock hydrocarbons. These are hydrocarbons whose mode of formation and chemical composition are identical to conventional hydrocarbons, but which are contained in a rock with very low porosity and virtually impermeable, making them impossible to produce using conventional methods. They are therefore classified within the large family of unconventional hydrocarbons, along with Canada's tar sands and Venezuela's heavy and extra-heavy oils.

The production of these hydrocarbons makes massive use of two techniques already commonly employed in the oil industry: horizontal drilling and hydraulic fracturing. Horizontal drilling makes it possible to penetrate the layer containing bedrock hydrocarbons over long distances (1 to 2 km), while hydraulic fracturing creates an artificial fracture that allows the hydrocarbons present to be drained towards the well. Due to the particular nature of these clays, the drainage radius and productivity of wells are relatively small, necessitating the multiplication of installations. It is this large number of production wells that accounts for a larger environmental footprint than in the case of a conventional deposit. This footprint is reflected in land use, water resource management and the risk of aquifer and air pollution. All current developments are aimed at reducing this environmental footprint and assessing the risks involved.

The rapid and widespread development of these bedrock hydrocarbons, in liquid (shale oil) or gaseous (shale gas) form, has shown that they can be produced at competitive costs. In the United States, the massive production of shale gas has led to a significant drop in the cost of methane, while the production of shale oil has enabled us to return to the peak production levels reached in the early 1970s. All source rocks sufficiently buried to have generated liquid or gaseous hydrocarbons are therefore potential targets for this type of production. Subsoil resources are therefore considerable, but these figures need to be weighed up against the low recovery rate and the large number of production sites. While it is still too early to define the importance of bedrock hydrocarbons in the future energy mix, it is reasonable to assume that in many sedimentary basins,...