As sickdude has pointed out the Schlumberger website is a great place to get an answer to most of your questions. But I would like to add, that unconventional gas plays comes in many form, and they may or may not recquire fraccing.
What is Unconventional Gas?
Natural gas is formed over thousands of years by the combination of pressure and heat on organic material trapped in rock. After natural gas is formed, the earth’s pressure often pushes the gas upward through small holes and cracks in rock until it reaches a layer of impermeable rock where the gas becomes trapped. It sits there in a “pool” until it is released from the ground by a drill bit providing a path to the surface. This is what we call conventional gas, the resource upon which our gas industry was built. But not all gas is found in these formations. In fact, there are a number of forms of unconventional gas that were created in formations without the permeability necessary to allow migration. These include:
• Tight Sands Gas – formed in sandstone or carbonate (called tight gas sands) with low permeability which prevents the gas from flowing naturally.• Coalbed Methane (CBM) – formed in coal deposits and adsorbed4 by coal particles.
• Shale Gas – formed in fine-grained shale rock (called gas shales) with low permeability in which gas has been adsorbed by clay particles or is held within minute pores and microfractures.
• Methane Hydrates – a crystalline combination of natural gas and water, formed at low temperature and high pressure in places such as under the oceans and permafrost.
