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o l\j ~ ao CHAPTER V VERIFICATION PROGRAM , This was the only location where water was found in the Dakota Sandstone during the observation well drilling. Water quality in the wells near the river was similar to that found in the observation wells on top of the dome and in the springs and seeps; however, the water in the Dakota Sandstone had a lower pH. Well Reentry The major portion of the verification program involved reentering, cleaning out, testing, and plugging three of the abandoned oil wells-- the Marland, Scott, and James Wells. The Scott and James Wells were selected in addition to the Marland because well logs indicated that they had also been inadequately plugged. Scot t Well Reentry work on the Scott Well was initiated in October 1980. The well was found to be intact and a cement plug was located at 1,94~ feet. Through geophysical logging, however, it was determined that the annular seal (between the well casing and the rock formations) was only parti- ally intact. This condition caused pressurized water to be isolated from the upper formations but allowed movement of water from the Entrada Sandstone into the shallower formations. Recorded reactions in the nearby observation wells verified the condition. Subsequently, the well was plugged to the surface with cement (December 1980). Marland Well The Marland Well was suspected to be the primary pathway for saline water to enter the shallow formations. Reentry began in December 1980, and it immediately became apparent that the original well casing was in a seriously corroded condition. Numerous cementing efforts were re- quired to stabilize the deteriorated casing as drilling progressed. The lower part of the well, from about 400 feet down to 640 feet, apparently collapsed while the drill bit was being removed in preparation for cementing of the lower 200 feet. Attempts made to clean the well and retrieve the tools proved unsuccessful, and the drill bit and 114 feet of drill pipe were abandoned in the well. " A second attempt to reenter the Marland Well was started in April 1981. Progress was much slower than expected because of the unstable casing and a need to use large diameter equipment. This reentry effort was halted after only 220 feet. In a final attempt at plugging, a parallel intercept well was drilled 16 feet from the original bore. The upper 220 feet of the Marland Well were recased with 5-inch PVC pipe so water levels in the original well could be monitored. The intercepting well was drilled vertically to I,OOO feet, and tests were conducted to identify formations and water sources in relation to the Marland Well. The upper 1,000 feet of the intercept well were then carefully cased with cemented steel. Using 17