Development of Radar-Controlled Directional Drilling Bottom Assembly for Geothermal Reservoirs

Abstract

Medium-radius horizontal directional drilling in geothermal reservoirs offers the potential for increasing the recovery of minerals from brine and the heat transfer rate in hydrothermal electricity generation. The technical challenges to be overcome in developing horizontal directional drilling technology are many. Exceedingly high reservoir temperatures require technology breakthroughs in designing electronics that can withstand the high-temperature environment. Geosteering of the bottom-hole assembly (BHA) requires low-frequency radar with antenna arrays with side- and forward-looking antenna patterns. The radar requires an electric-power generation supply and automated control signals for the gimbals. Solving these technical problems requires breakthroughs in the current state of the art.

Assuming that these technical challenges can be overcome, horizontal boreholes lined with high-temperature pipe can use super-heated steam to generate electricity using closed-circuit turbines. Because the construction area extends over the horizontal crosssectional area of the geothermal reservoir, the heat transfer can be maximized using multiple horizontal boreholes. The possibility of using distilled water circulating in a closed system eliminates the extreme scaling problem experienced in highly mineralized geothermal reservoirs, reducing the operating cost of producing electricity. Radar-controlled directional drilling can intercept geothermal reservoirs where brine flow pathway density maximizes. This paper describes the development of the radarcontrolled drilling hardware.