THE DEEP SUBSURFACE GEOLOGY, HYDROLOGY, AND ENHANCED GEOTHERMAL SYSTEMS (EGS) POTENTIAL OF NPR-3 (TEAPOT DOME), NATRONA COUNTY, WYOMING

RMOTC is located at the Teapot Dome oil field, aka the Naval Petroleum Reserve No. 3 (NPR-3). The field is thirty-five miles north of Casper, Wyoming, and is operated by the U.S. Department of Energy as a test site for new and developing oil and gas and renewable energy technologies.

At NPR-3 the Pennsylvanian Tensleep produces sufficient hot water for the generation of low-temperature geothermal energy. The average production temperature for the Tensleep Formation is 195°-200°F. In 2008 a 250 kW Organic Rankine Cycle power plant was installed to demonstrate small-scale geothermal power generation in an oil field.

NPR-3 is not located in an area of known high surface heat flow, so the produced water temperatures seen from the relatively moderate depths of 5,500 feet are anomalous for the area. Based on the temperatures observed from Tensleep production, the local geothermal gradient is 3.0°F per 100 feet of depth (55°C per km). The groundwater resource in the Tensleep Formation is continuously recharged from mountains to the west. The hydrologic system in the area apparently has the groundwater heated by proximity to deep basement rocks prior to entering into the Teapot Dome anticline.

Analysis of aeromagnetic and gravity data and 2D and 3D seismic surveys over the site indicate there is not a significantly deeper top of basement surface along the groundwater migration pathway. Explanations for the heat anomaly include (1) higher heat flux than projected near the sedimentary-crystalline basement interface, (2) deep fractures into the basement allowing groundwater flow down into the granite prior to entry into the Teapot Dome structure, (3) higher heat flow in the basement below NPR-3 due to radiogenic granite or a previously undetected buried magma body.

RMOTC plans to deepen an existing well into the granite at least 1,000 feet as a “science well” to find out additional information on the setting, including temperature profiling, a modern logging suite, and coring to obtain samples of the basement that can be further evaluated for geomechanical properties. This information should help to better understand the thermal gradient within the crystalline basement rock, presence of natural fractures, rubble zones or “granite wash”, and the potential for induced fracturing methods for an Enhanced Geothermal System (EGS) reservoir.