Overview of Deep Geothermal Production at the Peppermill Resort

Abstract

In 2009, Peppermill Resort Casino expanded its use of geothermal waters by drilling at depth into the Moana geothermal resource. The geothermal resource is of meteoric origin and is assumed to be heated by an intrusive body at depth. Past production of fluids from the resource was limited to shallow, Neogene clastic sediments. The first well drilled into the deeper Kat Peak formation was completed in 1988 and was completed as an injection well. In 2007, with the beginning of a large expansion to the facility, it was decided to make geothermal an integral part of the development plan. Two new deep wells were drilled in 2009 and 2010 to provide additional production and injection capacity. These wells demonstrated a significant improvement in temperature and flow over the earlier shallow wells. The use of acoustic and microresistivity logs, combined with other wireline logs and cuttings analysis, helped to develop a more detailed view of the resource. An intensely fractured zone occurs in the highly permeable andesite from approximately 2,500 ft to 3,400 ft. The majority of fractures in the Kate Peak trend northerly with a dip to the west. This data, with existing structural data, allows hypotheses regarding underlying controls of the Moana geothermal resource, as well as a foundation for further economic evaluation for commercial use.