History and unconventional gas generation

In the nearly 200 years of oil and gas exploration and development history, on oil and gas causes problems in the past have had a long heated debate in recent years controversy was underway.
Since the 1870s, oil and gradually formed the genesis of inorganic and organic produce to generate two schools. However, due to the world's oil and gas fields have been discovered in sedimentary distribution of 99.9% moderately important facts, especially in the 1970s, the French Tissot establish kerogen hydrocarbon evolution model is proposed kerogen late hydrocarbon doctrine, theory popularity of organic produce kerogen hydrocarbon theory swept the world, becoming the traditional sense of the dominant theory of oil and gas exploration. According to the theory and accumulation patterns found in reservoirs, people often view them as conventional oil and gas reservoirs.
However, in the late hydrocarbon kerogen theory widely accepted by the international oil industry at the same time, the world exploration and practice new discoveries of oil and gas on the traditional theory of challenges. For example, do not have a mature source rock areas have been found to exist "immature - low mature" oil, indicating the existence of a significant number of nature in the early generation of  unconventional gas  resources. World has been in the United States, the former Soviet Union, France, Venezuela and other 21 basins found 75 deeper than 6000 m of industrial oil and gas reservoirs. This can not be explained by the traditional theory, visible in a suitable geological and geochemical conditions, ultra-depth source rocks can still generate industrial-scale hydrocarbon gases. Since the 20th century, since the 1960s, Groningen gas field in the North Sea and elsewhere, a series of large gas discoveries were associated with Mesozoic and Cenozoic coal measures related to its gas composition and origin analysis shows that this is different from the kerogen Another said hydrocarbon gas. In addition, in recent years, inorganic theory once again cause for concern, there are many signs that the methane may also have inorganic sources. Exploration practice in many new discoveries of oil and gas generation is difficult to use traditional theory to explain, therefore, people will  Unconventional gas  such as natural gas.
The scientific community for similarities and differences between natural gas components, or the original parent material, build environment, differences in other aspects of occurrence needs further understanding, and thus on the concept of unconventional natural gas remains to be further determined. Now commonly known as unconventional gas can be roughly summarized as the following.
Coal seam gas and coal in coal refers to the dispersion of organic matter generated during the coalification gas, unconventional natural gas is the most important one.
CBM is designed specifically refers to the adsorbed state exists in the coal seam gas, coal gas is to describe the occurrence of a specific term, its meaning also commonly known as coal mine gas.
Dissolution of soluble gas, also known as high-pressure gas, refers to the oil and gas basins in a dissolved state occurs in a hydrocarbon gas formation water, abnormal formation pressure is often the main conditions for soluble gas enrichment.
shale gas in foreign countries mainly refers to the depth of 4000 meters below the natural gas resources in China usually refers nowadays mainly exploring layer (mostly 3500 m depth) below the gas resources.
In addition, unconventional gas  should also include organic reaction does not involve any role and processes of hydrocarbon or non-hydrocarbon generated gases, they belong to the inorganic gas.