The Use of Slim Hole Drilling Technology in the Hawaiian Scientific Observation Hole (SOH) Program: A Case History

Abstract

Prior to the initiation of the Scientific Observation Hole (SOH) program of July 1, 1988, the geothermal potential of the Kilauea East Rift Zone (KERZ) on the Island of Hawaii was assumed to approximately 500 megawatts of electrical energy. To test this assumption, the Hawaii Natural Energy Institute (HNEI) proposed a plan to assess Hawaii.s geothermal resource potential by core drilling small diameter observation holes along the KERZ and the Haleakala Southwest Rift Zone on Maui. The goals of the SOH program, as defined by the enabling legislation, were to Hawaii.s geothermal resource potential and stimulate geothermal exploration by the private sector. Approvals for geothermal activities in Hawaii must be coordinated with the Department of Health.s Office of Environmental Quality Control, the Department of Land and Natural Resources, and the Planning Commission of the County in which the activity is planned. Required public hearings were held and agency approvals coordinated to ensure that all necessary permits were issued. To assess the geothermal potential of the KERZ, an array of four holes, three of which were drilled, were sited along the long axis of the within existing Geothermal Resource Subzones (GRS). These holes were drilled by Tonto Drilling Services, Inc. using a Universal drilling rig. Two holes were spaced to provide step-out coverage between or beyond existing and planned geothermal production wells, and two holes were located with the intent of .pairing. the SOHs with production wells to test for permeability across the rift zone. Successful drilling techniques, casing procedures, and a mud program were devised as the geologic formation became known and its characteristics noted.