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Development of effective exploitation strategies requires accurate characterization of geothermal reservoirs. Geophysical data are potentially the most powerful and cost effective means of exploration and characterization, providing images of the subsurface structures prior to extensive drilling. Once production is initiated, geophysics is commonly used to monitor changes in the reservoir, tracking the development of steam caps, changes in pore fluid pressure, and understanding the effects of re-injection.

NER focuses on the development and constraint of physical models to improve interpretations of geophysical observations in geothermal reservoirs. Effective characterization and monitoring of geothermal reservoirs requires a fundamental understanding of the geophysical properties of reservoir rocks and fracture systems as well as determining their relation to structural, hydrological, and geochemical characteristics. This is best attained through integration of core analysis, log analysis, and interdisciplinary studies of geological, petrological, and geophysical data. To help meet these needs, NER conducts studies to develop an understanding of the role of stress, temperature, fluid pressure, mineralogy, pore structure, rock type, degree and type of alteration, and core scale heterogeneity on key physical properties. We have worked extensively on The Geysers and Awibengkok core, which has allowed us to make use of excellent supporting data.

Key areas of technical focus include:

• Systematic study of shear weakening phenomena (rock-water interaction)
• mineralogic and textural controls
• effect of temperature and brine chemistry
• partial saturation
• pressure solution
• fracture properties
• Quantifying core scale heterogeneity
• mechanical
• electrical
• flow
• influence of heterogeneity on fracture properties 
• Integration and scaling of seismic, electrical, and flow properties
• experimental study of shear weakening of rock joints
• integration of core scale data into fractured rock models
• relationships between fracture systems and microseismicity

Selected Reports

• 2003 DOE Final Report, with synthesis of Awibengkok and The Geyers core data
• Interpretation of Field Seismic Tomography at The Geysers
• More on Interpretation of Field Seismic Tomography at The Geysers
• 1999 GRC Transactions preprint concentrating on Awibengkok velocities
• 2001 GRC Transactions preprint concentrating on Awibengkok electrical properties

Suggested Reading

• Ross et. al Geysers interpretation
• GunasekeraJGR.pdf
• MammothTom.pdf
• GRCTomo2004.pdf

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