Unique aspects of drilling and completing hot, dry rock geothermal wells : Carden, R S; Nicholson, R W; Pettitt, R A; Rowley, J C J Pet EngngV37, N5, May 1985, P821–834

Abstract

The drilling and completion of wells in hot, non-porous crystalline basement rock has challenged conventional rotary and directional drilling tools, procedures, and instruments used for oil and gas drilling. Drilling operations at the Fenton Hill Hot Dry Rock (HDR) Geothermal Test Site have led to numerous developments needed to solve the problems caused by a very harsh downhole environment. A pair of deep wells were drilled to approximately 15,000 ft (4.6 km); formation temperatures were in excess of 600/sup 0/F (300/sup 0/C). The wells were directionally drilled, inclined at 35 degrees, one above the other, in a direction orthogonal to the least principal stress field. The well site is near the flank of a young silicic composite volcano in the Jemez Mountains of northern New Mexico. The completion of this pair of wells is unique in reservoir development. The lower well was planned as a cold water injector which will be cooled by the introduced water from the static geothermal gradient to about 80/sup 0/F (25/sup 0/C). The upper well will be heated during production to over 500/sup 0/F (250/sup 0/C). The well pair is designed to perform as a closed loop heatextraction system connected by hydraulic fractures with amore » vertical spacing of 1200 ft between the wells. These conditions strongly constrain the drilling technique, casing design, cement formulation, and cementing operations. The completion of these two wells by hydraulic fracturing is proving to be very difficult, due to the large water volumes required, problems with zone isolation, logging, and extreme temperatures. New and upgraded technologies have been developed to resolve these difficulties.« less