An Analysis of Gravity and Geodetic Changes Due to Reservoir Depletion at The Geysers, Northern California

Authors: Denlinger, Roger P.; Isherwood, William F.; Kovach, Robert L.
Keywords: Subsidence; Reservoir Depletion; Gravity; Leveling; USA; California; Geysers; Thermal Contraction; Strain; Pore Volume; Mass Production; Gravity Survey; Well Data; Reservoir Engineering; Pore Fluids; Recharge; Steam Production; 1973-1977 Period; Water Tab
Conference: Geothermal Resources Council Transactions Session: Exploration; Geophysical surveys; Gravity surveys; Subsidenc
Year: 1979 Language: English
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Abstract: In this paper gravity and geodetic data are combined with reservoir engineering studies to place upper and lower bounds on the volume and pore fluid mass changes within the depleted portion of the steam reservoir at the Geysers. We combined the gravity and temperature data to constrain the changes in pore fluid mass distribution due to fluid depletion, and thus limited the drainage volume to lie between 15 and 25 cubic km. We then modeled the surface geodetic data to determine values of strain between 3. and 8. x 10-5 for these drainage volumes. We determined that this strain could be induced either mechanically or thermally, and there is presently no way of distinguishing thermal from mechanical strain.
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