| Title | Stratigraphic and Structural Framework of the Proposed Fallon FORGE Site, Nevada |
|---|---|
| Authors | Nicholas H. HINZ, James E. FAULDS, Drew L. SILER, Brett TOBIN, Kelly BLAKE, Andrew TIEDEMAN, Andrew SABIN, Douglas BLANKENSHIP, Mack KENNEDY, Greg RHODES, Josh NORDQUIST, Stephen HICKMAN, Jonathan GLEN, Colin WILLIAMS, Ann ROBERTSON-TAIT, Wendy CALVIN |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Great Basin, Fallon, Nevada, EGS, temperature, permeability, stratigraphy, structural setting |
| Abstract | The proposed Frontier Observatory for Research in Geothermal Energy (FORGE) at Fallon site lies within and adjacent to the Naval Air Station Fallon (NASF) directly southeast of the town of Fallon, Nevada, within the broad Carson Sink basin in west-central Nevada. The site is located on two parcels that include land owned by the NASF and leased and owned by Ormat Nevada, Inc. The Carson Sink in the vicinity of the Fallon site is covered by Quaternary deposits, including alluvial fan, eolian, and lacustrine sediments. Within the primary FORGE footprint, three wells penetrate the entire Neogene section and terminate in Mesozoic basement. Review of ~14,500 meters of core, cuttings, thin sections of core and cuttings, and well logs have refined earlier summary studies on the stratigraphic and structural framework. Late Miocene to Quaternary basin-fill sediments are 0.5 to 1 km thick and overlie Miocene volcanic and lesser sedimentary rocks. The volcanic section is 0.7 to 1.1 km thick and dominated by Miocene mafic lavas. The Neogene section rests nonconformably on heterogeneous Mesozoic basement, which consists of Triassic-Jurassic metamorphic rocks intruded by Cretaceous granitic plutons. These Mesozoic units are widespread across western Nevada and were formed in the back arc of the Sierran arc. Review of more than 250 km of seismic reflection profiles and gravity models indicate that the FORGE footprint occupies a broad, gently west-tilted block between a synclinal accommodation zone to the west and an anticlinal accommodation zone to the east. Quaternary faults have not been observed within the proposed FORGE site. The documented temperatures, permeability, and lithologic composition of potential reservoirs fall well within the ranges specified by DOE for FORGE. The well data indicate that a sizeable area (~4.5 km2) has adequate temperatures in crystalline basement but lacks sufficient permeability within the proposed FORGE site. There are at least three possible, competent target formations in Mesozoic basement for stimulation in the FORGE project area: 1) Triassic to Jurassic felsic metavolcanic rocks, 2) Jurassic metaquartzite, and 3) Jurassic to Cretaceous granitic intrusions. These units make up at least 3 km3 in the project area and have target temperatures of ~175 to 215° C. The documented temperatures, low permeability, and basement lithologies place Fallon in the target range of FORGE. |