country's conventional gas industry for thousands of years.
The North Sea is also thought to contain substantial quantities of unconventional petroleum.
The main difference between conventional and unconventional accumulations is the ease with which oil and gas flows through the formation. Geologists measure this permeability in Darcy units. Permeability for the giant carbonate and sandstone reservoirs of the Middle East is a thousand times or more than for shale formations.
Until the advent of horizontal drilling and hydraulic fracturing, there was no way to extract oil and gas in commercial quantities from low-permeability rock formations such as shale. But by creating a network of tiny fissures in the rock formation, hydraulic fracturing can enable oil and gas to flow through rocks that were formerly impermeable.
However, it is important not to overstate the differences between conventional and unconventional production. Conventional oil and gas producers regularly use hydraulic fracturing, acidizing and other treatments to stimulate production from wells.
Hydraulic fracturing treatments have been performed more than a million times in the United States since 1947, in most cases on "conventional" oil and gas wells, according to the National Petroleum Council ("Prudent Development: Realising the Potential of North America's Abundant Gas and Oil Resources" 2011).
Old and New Industries
The U.S. Energy Information Administration (EIA) estimates there are 6,622 trillion cubic feet (tcf) of technically recoverable shale gas resources in the United States and 32 other countries.
To put this in perspective, the world's proven resources of (conventional) natural gas are about 6,600 tcf, and total technically recoverable resources are roughly 16,000 tcf, so shale gas extends the conventional resource base by 40 percent ("World Shale Gas Resources: An Initial Assessment of 14 Regions Outside the United States" Apr 2011).
Some of the biggest shale accumulations are likely to be found in countries that already have substantial conventional gas resources. The United States is thought to have 862 tcf of shale gas, Libya's shale resources are put at 290 tcf, and Algeria's at 231 tcf.
The EIA study did not assess shale accumulations around the Middle East Gulf or in Russia and the other countries of the former Soviet Union, but they are thought to be extensive.
The report did not assess shale oil resources at all. But given the geology of total petroleum systems, it is very likely large shale accumulations will be found in the same areas and countries that already have large accumulations of conventional oil.
Crude-laden shale formations like North