Where is it found?
Shales are present worldwide in the sedimentary sequence. Large sedimentary basins, where sediments accumulated over millions of years, are favorable places to find large extent shale deposits of sufficient thickness. Certainly not all shales contain reasonable quantities of natural gas. Geologic modeling can lead exploration geologists to promising locations, and the subsequent investigation of drilled rock samples will eventually give information on the gas content of the shales.
Since large-scale shale gas production is ongoing only in North America, information on the location of gas shales worldwide is rather incomplete. The 2013 U.S. EIA report "Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States" summarized information on 95 shale basins in 41 countries (Fig. 1), including brief descriptions of the geology, reservoir properties, resources and activities in individual basins.
Fig. 1: Map of major shale gas basins in 41 countries (EIA, 2013).
North America
The large shale gas formations of North America are shown in Fig. 2. Many of the shales have been proven to contain natural gas and are already being exploited. Large-scale shale gas production started in the U.S. in the Barnett shale, Texas, in the late 1990s.
Fig. 2: Natural gas resources of North America (IEA, 2012).
Europe
Whether the large shale deposits in Europe (Figs. 3-5) are promising for large-scale shale gas production is in most cases yet unknown. A few prospective wells have been drilled, and scientific investigations are now being carried out to find and compile data on where to locate the shales and also how they formed.
A prominent effort in this respect is the project "Gas Shales in Europe" (GASH). It is the first European interdisciplinary shale gas research initiative. Coordinated by GFZ German Research Centre for Geosciences, GASH is developing a GIS-based European black shale database, and is conducting 12 research projects with a multinational expert task force drawn from research institutions, geological surveys, universities and consultants.
Fig. 3: Prospective shale gas basins of Eastern Europe (EIA, 2013).
Fig. 4: Shale gas basins and coalbed methane of Western Europe (IEA, 2012).
Fig. 5: Assessed shale gas basins of Poland (EIA, 2013).
