| Title | A Play Fairway Analysis for Structurally Controlled Geothermal Systems in the Central Cascades Arc-Backarc Regime, Oregon |
|---|---|
| Authors | Philip E. WANNAMAKER, Andrew J. MEIGS, John D. TRIMBLE, Ellen A. LAMONT, B. Mack KENNEDY, Joseph N. MOORE, Virginie MARIS, Eric L. SONNENTHAL, Gregory D. NASH |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | play fairway analysis, central Cascades Oregon, exploration, GIS |
| Abstract | A research team with membership from the University of Utah/EGI, the Oregon State University, and Lawrence Berkeley National Laboratory have carried out a play fairway analysis (PFA) for geothermal resources in the Central Cascades arc-backarc volcano-tectonic regime of central Oregon. This is a unique region for geothermal exploration because active Basin and Range (B&R) extension is superimposed upon and contemporaneous with subduction arc magmatism. Cumulative heat flow along the N-S strike grows from negligible values at the north end to more than 300 MW in the space of ~100 km concentrated in the northern portion of the PFA area. Perhaps surprisingly then, no geothermal resources leading to construction of an electricity-producing power plant have yet been identified in the U.S. Cascades. Succinctly, our PFA adds to understanding of the potential sources of heat and permeability in the region, which are the two principal criteria for establishing a geothermal resource. A constraint of the PFA project was that only existing data could be analysed, albeit using new and state-of-the-art methods. A challenge in this PFA region is the paucity of existing data, presumably related to the lack of historical geothermal development as well as some non-trivial access. Criteria selected for establishing heat potential include direct heat flow measurements in boreholes, magnetotelluric (MT) low resistivity anomalies, fluid geochemistry, and proximity to recent volcanic eruptions. Permeability is established by fault density, propensity of faulted sub-regions for slip or dilation, and MT low resistivity anomalies. Heat source and permeability potential are expressed in terms of their individual common risk segment maps, with a color scheme using green for most favorable (low risk) and red for least favorable (high risk). Due to data scarcity, we need to mix approaches based upon probability kriging and conceptual global models based on experience in other environments. For dominantly andesitic arc type resources, inferred heat sources and permeability as well as land and transmission access suggest that prospective areas may lie along a NW-SE fault trend passing from Breitenbush Hot Springs area through the Mt Jefferson volcanic edifice into the backarc area, as well possibly as areas nearby to the north of Mt Jefferson. For dominantly extensional type resources, new areas worth examining could lie along diffusely oriented normal faulting extending north of Newberry volcano and into the Warm Springs region. |