Geothermal hot dry rock drilling activities at Fenton Hill in the Jemez Mountains of northern New Mexico encountered problems in designing drilling fluids that will reduce catastrophic lost circulation. Four wells (GT-2, EE-1, EE-2, and EE-3) penetrated 733 m (2405 ft) of Cenozoic and Paleozoic sediments and Precambrian crystalline rock units to +4572 m (+15,000 ft). The Cenozoic rocks consist of volcanics (rhyolite, tuff, and pumice) and volcaniclastic sediments. Paleozoic strata include Permian red beds (Abo formation) and the Pennsylvanian Madera and Sandia Formations, which consist of massive limestones and shales. Beneath the Sandia Formation are igneous and metamorphic rocks of Precambrian age. The drilling fluid used for the upper sedimentary formations was a polymeric flocculated bentonite drilling fluid. Severe loss of circulation occurred in the cavernous portions of the Sandia limestones. The resultant loss of hydrostatic head caused sloughing of the Abo and of some beds within the Madera Formation. Stuck pipe, repetitive reaming, poor casing cement jobs and costly damage to the intermediate casing resulted. The Precambrian crystalline portion of the EE-2 and EE-3 wells were directionally drilled at a high angle, and drilled with water as the primary circulating fluid. Due to high temperatures (approximately 320 C (608 F) BHT) and extreme abrasiveness of the deeper part of the Precambrian crystalline rocks, special problems of corrosion inhibition and of torque friction were incurred. Several techniques were attempted to solve these problems but have met with varying degrees of success
