Abstract
A procedure was developed to allow manged temperature drilling of the granite heat source of an enhanced geothermal well. It was shown that the procedure created economies due to the removal of the MPD equipment, the requirement to stage-in and the need to circulate chilled water. It was determined that the procedure could be deployed in any well provided that it was considered at the outset. It is indicated that time spent on drilling the heat source can be reduced. The procedure involved the installation an additional casing called a parasite string. The installation of the parasite string allowed for the installation of temperature sensing equipment that is able to provide an accurate down hole temperature gradient. The installation of the parasite string also allowed for the automation of the temperature control. The installation of the parasite string made operations safer because super heated water was never allowed to the surface. It was shown that the installation of an additional string of casing did not interfere with the final hole diameter and that it was possible to drill into the hot dry rock with an 8 ½" bit and 7" production tubing for the hot water. It was shown that the heat source could be drilled with plain water resulting in significant savings in preparation and maintenance of a drilling fluid. The use of the parasite string resulted in a reduction in the area required for cooling ponds and in an area where cooling ponds may not be acceptable a refrigerated water chiller would be all that was required. It was determined that after the well was drilled and completed an insulating gel material could be installed in the two annuli created by the parasite string. The insulation would enhance the life of well by conserving the heat in the production tubing.
