History of Natural Gas Seeps in the Northern San Juan Basin

Historically documented naturally occurring gas seeps throughout the San Juan Basin existed prior to oil and gas drilling operations. Coal-miners found pockets of methane in mines in the northern part of the Basin. Figure 3 shows a coal prospect in the Fruitland coal outcrop.

Figure 3: Prospect in Fruitland coal outcrop

Shallow water wells penetrating Fruitland and Menefee coalbeds around the Basin rim have historically produced methane gas. Especially notable in La Plata County, Colorado, are seeps at the northern and western rim of the San Juan Basin. Known gas seeps include the Carbon Junction area where the Animas River crosses the Fruitland Formation. At this location methane and hydrogen sulfide seeps were commonly recognized as early as the 1930’s (Amoco, 1996). Local residents noted as early as 1920 that “ a “rotten egg smell” is being emitted from the Carbon Junction Area” (Whitton, personal communication, 1996). Another well-known site of historic gas seepage is a topographic low in the Hogback Monocline between Valencia Canyon and Iron Springs Canyon on the western rim of the San Juan Basin. Historically emitting odors of “rotten egg gas” (hydrogen sulfide), this pass through the hogback was known by old-timers as “stink hill”. Other areas of seepage existed at the northeastern edge of the San Juan Basin rim. Ranchers ignited escaping natural gas from water faucets, holes punched in iced-over streams, or known soil seeps in entertaining pyrotechnic displays impressing new-comers or merely celebrating the Christmas Season (Halverson, 1994; Hocker, 1994). Dugan (1990) recalls a mention of a gas seep near Bondad, Colorado and a gas seep in a drill rig cellar in 1955. In approximately 1968, several water wells were drilled in the Cedar Hill, New Mexico area, but the water was unusable due to the strong sulfur odor (Kearl, 1988). Forty years ago a group of local youngsters who inadvertently cast a campfire ember into the Los Pinos River were duly impressed when the surface of the river ignited in a flash (Hocker, 1999).

As early as 1980-1985, new seeps not associated with Basin rim outcrops, but interior to the Basin, appeared to be forming in pastures in the Animas River Valley south of Durango near Bondad, Colorado and Cedar Hill, New Mexico (Shuey, 1990; Beckstrom and Boyer, 1991). Rural property owners in the Cedar Hill and Bondad areas noticed bubbles in the Animas River and in their tap water. Water well pumps cavitated as natural gas exsolved from the groundwater so rapidly that some pumps failed to perform. Several pump houses exploded when methane gas accumulated in the confined spaces and were ignited by a spark, possibly generated by a pressure switch or electric motor brushes. One well owner in the Cedar Hill area reportedly shot a high-powered rifle into his water well casing to develop the well, and inadvertently started the well on fire. Gas seeps in soils that overlie Mesaverde sandstone outcrops were noted in the mid-1990’s as manifesting patches of dead grass in pastures northeast of Durango along CR #240.