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2.0 MINING AND OIL AND GAS DEVELOPMENT 2.1 MINING DEVELOPMENT 1~Iining in the area was preceded by the attempted development of the area known as the "second right." This area is located south of the affected area, and was first developed in January 1988. A geologic anomaly was encountered during development that forced abandonment. A series of fault location holes were drilled to attempt to locate the magnitude, direction, and extent of the fracture zone. Results of this program did not reveal any faults; however, a structural downwarp, similar to a monocline, was infetted. The monocline appears to decline at a rate of 8 percent [o the east over a distance of 400 feet. The fractured zone was interpreted to trend north-south at 6,600 feet above mean sea level (AMSL). For reference, the surface of the Purgatoire River is at 7,010 feet AMSL, making a fracture zone approximately 410 feet below surface grade at the location of the second right development. Permanent seals were emplaced to separate [he fracture zone from the mine. In addition, vent wells were installed into they second right development, and methane has historically and is currently being extracted from the wells. After the second right development was abandoned, a development of the mine was turned north under the :Purgatoire River. Development of entries under the river began in 1989, and the first longwall panels were mined on the north side of the river in 1993. A ventilation shaft was installed for these activities in late 1989 and early 1990. Mining at the site ceased in December 1995. :Pumps were deactivated after mining ended and the mine is currently filling with water. In addition, gas is recovered from [he mine by active ventilation. The mine is therefore maintained under negative pressure. 2.2 NATURAL GAS DEVELOPMENT Gas development at the site has focused on coal bed methane (CBM). CBM is principally extracted from wells installed in coal seams [hat contain high volumes of gas. The methane is liberated by extracting water from the coal seam via the well, resulting in decreased pore pressure in the coal. Typically, methane is then piped from the wells to compressors, and then to consumers. 'There aze two CBM wells at the site. These wells are known as Picketwire 28-10 and Picketwire 28-I I. ' Picketwire 28-10 is the eastern well and Picketwire 28-11 is the western well (Figure 1). We1128-10 was spudded on September 24, 1990, and Well 28-11 was spudded on October 25, 1990. ' Well reports for We1128-10 indicate that the ground level at the site was 7,018 feet AMSL. The well was first drilled by emplacing a surface casing (conductor) by drilling with a 17-1/2-inch bit to 25 feet, [hen placing the 13 3/8-inch conductor pipe. The conductor pipe was cemented into place, and drilling was commenced with a ' 12 1/4-inch bit to 207 feet depth, when the surface conductor washed out and drilling was ceased to recement the conductor. Drilling continued to 448 feet, where an 8 5/8-inch casing was set at 438 feet. Drilling then continued with a 7 7/8-inch bit to 1,550 feet, where a 5 1/2-inch production casing was set. ' When well 28-10 was drilled, the temperature log indicted that gas was entering the borehole at approximately 504 feet below ground surface (bgs). No circulation to the surface was noted during the 8 5/8- inch casing run. When the 5 1/2-inch casing was cemented, gas was noted flowing between the 8 5/8-inch t annulus, gas pressure of 20 to 30 pounds per square inch (psi) was still noted in the annulus between the 8 5/8-inch and 5 1/2-inch casing. A suspected fault zone was noted at 63-feet. Analysis of the bond log for the casing cement indicates that there is no cement above 450 feet and that the bonding is possibly poor from 450 ' 7.92-McW_(Z 14.04) 2-1