HR: 16:45h
AN: V54C-04    [Abstracts]
TI: ANALYSIS OF 3D MAGNETOTELLURIC MEASUREMENTS OVER THE COSO GEOTHERMAL FIELD
AU: * Newman, G A
EM: ganewman@lbl.gov
AF: Earth Sciences Division Lawrence Berkeley Laboratories, One Cyclotron Road MS 90-1116, Berkeley, Ca 94720, United States
AU: Gasperikova, E
EM: EGasperikova@lbl.gov
AF: Earth Sciences Division Lawrence Berkeley Laboratories, One Cyclotron Road MS 90-1116, Berkeley, Ca 94720, United States
AU: Hoversten, M
EM: HOVG@chevron.com
AF: Chevron Corporation Seismic Analysis & Property Estimation, R&D, 6001 Bollinger Canyon Rd, D1046, San Ramon, Ca 94583, United States
AB: We have carried out an investigation of the Coso Geothermal field utilizing a dense grid of magnetotelluric (MT) stations plus a single line of contiguous bipole array profiling over the east flank of the field. Motivation for this study is that electrical resistivity/conductivity mapping can contribute to better understanding of enhanced geothermal systems (EGS) by imaging the geometry, bounds and controlling structures in existing production, and by monitoring changes in the underground resistivity properties in the vicinity of injection due to fracture porosity enhancement. Initial analysis of the Coso MT data was carried out using 2D MT imaging technology to construct a starting 3D resistivity model from a series of 2D resistivity images obtained using the inline electric field measurements (Zxy impedance elements) along different measurement transects. This model was then refined through a 3D inversion process. The 3D resisitivity model clearly showed the controlling geological structures influencing well production at Coso and shows correlations with mapped surface features such as faults and regional geoelectric strike. We have also correlated the model with an acoustic and shear velocity model of the field to show that the near-vertical high conductivity (low resistivity) structure on the eastern flank of the producing field is also a zone of increase acoustic velocity and increased Vp/Vs ratio.
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting