The San Juan Basin of southwestern Colorado has a
long history of methane gas production.
Several formations have been extensively developed for this
resource. Since the 1980’s, the
Fruitland Formation’s coalbed methane resource has been the main development
target. These coalbeds are continuing
to be developed with possible associated side effects manifested. Methane gas seeps, groundwater
contamination, and coalbed fires have been discovered. These conditions may be exacerbated by
continued production of water from the Fruitland coalbeds. Gas well water production could conceivably
influence the potential for spontaneous combustion of near-surface coals due to
the quantity of water withdrawn through pumping as compared to water level
fluctuations attributable to normal seasonal variations as a product of
precipitation and normal recharge alone.
Fruitland water extraction could also play a part in drawing ambient air
into the coalbeds, providing oxygen necessary for combustion and facilitating a
resurgence of dormant (smoldering) coal fires.
Increases in methane content of soils overlying
Fruitland coalbeds, lowering of water tables in domestic and water monitoring
wells drilled into the basin rim coals, fires in Fruitland coalbeds, alignment
of recently killed vegetation with underlying coal outcrops harboring high
methane concentrations/depleted oxygen, and an apparent intensification of
naturally occurring methane/hydrogen sulfide seeps have all been noticed since
the early 1990’s. These occurrences have been documented in a series of
research reports and studies commissioned and conducted by regulatory agencies,
the oil and gas industry and local government agencies. This time-span is concurrent with coalgas
production from the Fruitland coalbeds in the San Juan Basin. In a recent
report on environmental monitoring at the northern rim of the San Juan Basin
(Oldaker, 1999), a correlation between bottom hole pressure decreases at Basin
rim shut-in gas wells and water monitoring wells with down-dip water production
from Fruitland coalgas wells was termed probable.
The COGCC 3M Project, which includes strategies to
map, monitor and model significant environmental and reservoir effects of
Fruitland coalbed development was launched in 1999, as a continuation of the
efforts already inaugurated by the Southern Ute Indian Tribe and the Bureau of
Land Management. The Colorado Oil and Gas Conservation Commission, the Southern
Ute Indian Tribe, and the Bureau of Land Management’s San Juan Field Office
support this 3M Project. This effort to
understand Basin dynamics related to CBM development is critical due to
anticipated future CBM development.
Human health and safety issues, vegetation losses, environmental
degradation, and oxidation of coal reserves loom as potential associated
consequences of intensified gas development.
New techniques to mitigate coalbed dewatering effects
along the Basin rim where the Fruitland coalbeds are exposed may be initiated
during 1999. Based upon the results of
these and other preliminary pilot projects, the most effective mitigation
techniques can be determined for future implementation as necessary.
Recent indications of environmental degradation at an
increasing number of sites both on and off the Southern Ute Indian Reservation
lead to the concern that these conditions may proliferate. The nature and severity of potential impacts
of continued Fruitland coalgas production and additional gas wells drilled
close to the San Juan Basin rim need to be more fully understood. Computer model projections and the results
of proposed pilot mitigation efforts should enable well-founded regulatory
responses to predictable events. Until
projected effects are better understood, further approvals of infill drilling
development in the Ignacio-Blanco Field, (particularly those in proximity to
the outcrop) must be seriously scrutinized.