Tight Natural Gas
Another form of unconventional natural gas is referred to as tight gas. This is gas that is stuck in a very tight formation underground, trapped in unusually impermeable, hard rock, or in a sandstone or limestone formation that is unusually impermeable and non-porous (tight sand).
In a conventional natural gas deposit, once drilled, the gas can usually be extracted quite readily, and easily. A great deal more effort has to be put into extracting gas from a tight formation. Several techniques exist that allow natural gas to be extracted, including fracturing and acidizing. However, these techniques are also very costly. Like all unconventional natural gas, the economic incentive must be there to incite companies to extract this costly gas instead of more easily obtainable, conventional natural gas.
Tight gas makes up a significant portion of the nation's natural gas resource base, with the Energy Information Administration (EIA) estimating that, as of January 1, 2000, 253.83 Tcf of technically recoverable deep natural gas exists in the U.S. This represents over 21 percent of the total recoverable natural gas in the United States, and represents an extremely important portion of natural gas resources.