Oil and Gas at Your Door? (2005 Edition) - Earthworks

Oil and Gas Development and Impacts
Development of Nonconventional Gas and Oil
Forward-thinking landowners may want to investigate the possibility of unconventional reservoirs
beneath their land, since it is likely that more non-conventional oil and gas deposits will
be developed in the near future. This is certainly happening with the nonconventional coalbed
methane gas deposits.
Nonconventional gas includes gas trapped in coal formations (coalbed methane); and low-permeability
sandstone (tight sands) and shale formations (gas shales). These three types of natural
gas are currently being exploited in some areas of the U.S., and will be discussed in this section.
Other nonconventional natural gas resources, such as gas hydrates, are not likely to become
commercially viable for decades to come. 150 Consequently, they will not be discussed in this guide.
Nonconventional oil deposits include heavy oils, tar sands and oil shales. As mentioned previously,
petroleum is a broad term for hydrocarbons that includes gases, highly fluid “light” oils,
viscous “heavy” oils, tars and bitumens. Today, light oils comprise approximately 95 % of petroleum
production. 151 As will be discussed later in this section, when compared to conventional
deposits and methods, the amount of work required to produce an equivalent amount of crude
oil from tar sands or oil shales makes it cost prohibitive under most circumstances. 152
COALBED METHANE (CBM)
As many landowners in Wyoming, Montana, Colorado, New Mexico and Alabama can attest, an
increasingly significant source of natural gas is coalbed methane (see the Introduction chapter
for a map of CBM producing areas). Two decades ago, coalbed methane was not a highly profitable
source of natural gas. By the year 2004, however, CBM accounted for more than 8% of
natural gas production in the U.S. 153
According to the CBM Association of Alabama, 13% of the land in the lower 48 United States
has some coal under it, and in all coal deposits methane is found as a byproduct of the coal
formation process. Historically, this methane was considered a safety hazard in the coal mining
process and was purposely vented to the atmosphere. Recently, however, companies have
begun to capture the methane found in coal mines, as well as recover methane from coalbed
deposits that are too deep to mine. 154
Coal beds are an attractive prospect for development because of their ability to retain large
amounts of gas—coal is able to store six to seven times more gas than an equivalent volume of
rock common to conventional gas reservoirs. 155 On a daily basis, however, CBM wells typically
do not produce as much gas as conventional wells. 156 In most regions of the U.S., coalbed
methane wells produce between 100 and 500 thousand cubic feet (Mcf) per day, while the
average conventional well in the lower 48 states produces approximately 1.7 million cubic feet
(MMcf) per day. 157 There are, however, some extremely productive coalbed methane areas, such
as the San Juan basin in Colorado and New Mexico, where some wells produce up to 3 MMcf
of methane per day. 158
The amount of methane in a coal deposit depends on the quality and depth of the deposit. In
general, the higher the energy value of the coal 159 and the deeper the coal bed, the more
methane in the deposit. 160
Methane is loosely bound to coal—held in place by the water in the coal deposits. The water contributes
pressure that keeps methane gas attached to the coal. In CBM development, water is
removed from the coal bed (by pumping), which decreases the pressure on the gas and allows
it to detach from the coal and flow up the well.
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