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Specifications for Fracture Pretest Boreholes Installed on the <br />Walls (Ribs) of the Colony Mine Tunnels <br />Three short test boreholes A, B, and C, each 25-30 feet long and 3.75 inches in <br />diameter, have been installed in three tunnels at the Colony Mine experiment <br />site. All three were drilled with a 5 degree inclination, at an elevation 4 feet <br />above the tunnel floor (7082 feet above sea level). <br />The three boreholes were drilled as part of the early fracture pretests described <br />in ExxonMobil's submission to the Division of Reclamation, Mining and Safety, <br />dated August 30, 2007. Each borehole was cased with a 25 foot long, 2.875 inch <br />diameter casing. The casings were 6.4 pound-per-foot, L-80 grade steel casing. <br />They were installed in 2, 5, and 6 foot lengths with threaded connections. The <br />casings were cemented in place. A smaller diameter pilot hole was drilled out 2- <br />5 feet from each cased hole. The pilot holes were hydraulically fractured with <br />colored cement-based grout to study the propagation directions, and pressure <br />requirements of hydraulic fractures in the mine. The hydraulic fractures created <br />in the tests were designed to extend 25 feet or less from the pilot holes. <br />Observation holes were drilled to locate each of the pretest fractures, and these <br />holes were left uncased. <br />The photograph below illustrates the trajectory and casing head fastening <br />assembly used in each of the three fractured boreholes.