Geodetic analysis of reservoir depletion at the Geyser steam field in northern California

Journal of Geophysical Research Solid Earth
By: , and 

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Abstract

Reservoir depletion at the Geysers from 1974 to 1977 is evident in measured changes in gravity, surface strain, and pore pressure drainage. The drainage area increased about 20%, the maximum gravity decrease was about −120 μGal, and the maximum elevation change was about 6 cm during this period. Since the net mass withdrawal is known, it may be combined with the gravity change to estimate a drainage volume. The maximum drainage volume is 25 km3. Because the depth of the caprock and extent of the pore pressure drainage is known, this volume limit implies that no significant mass withdrawal occurs below a depth of 4 km. The ratios of surface elevation changes to horizontal contraction coinciding with the drainage area imply an equant drainage geometry, assuming that fluid production produces negative dilatation. Using the same cylindrical geometry used to model the gravity, negative dilatational strain rates of 4 to 5 × 10−5/yr were found to produce the observed surface displacements. The likelihood of boiling in the system to produce steam combined with apparent large bulk moduli (from seismic velocities) and small pore pressure declines suggest that most of the reservoir contraction is due to cooling.

Publication type Article
Publication Subtype Journal Article
Title Geodetic analysis of reservoir depletion at the Geyser steam field in northern California
Series title Journal of Geophysical Research Solid Earth
DOI 10.1029/JB086iB07p06091
Volume 86
Issue B7
Year Published 1981
Language English
Publisher American Geophysical Union
Description 6 p.
First page 6091
Last page 6096
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