Precise Gravimetry and Geothermal Reservoir Management

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Conference Paper: Precise Gravimetry and Geothermal Reservoir Management

Abstract
Modern portable gravimeters can routinely achieve a5 ugal uncertainty with careful measurementprocedures involving multiple station occupations inthe same day, and stacking of readings over at least15 minutes during each occupation. Although furtherimprovements in gravimeter accuracy are feasible,other practical factors relating to repeat surveys ofgeothermal fields make such improvements oflimited value. The two most important factors arebenchmark elevation variations (3 ugal/cm) andgroundwater level fluctuations (5-10 ugal/m). Dualfrequency GPS receivers can give elevations to about2 cm after 30 minutes of recording, and for reducinggroundwater uncertainties, repeating the surveysduring the same season coupled with checks ofgroundwater monitor wells is advisable.Simple models are presented for the gravity effects ofevolving steam zones at Wairakei field, Dixie Valleyfield, and The Geysers field. Changes during themain pressure-drawdown phase of developmentprobably caused gravity decreases of 200 - 1000ugal, but subsequent changes would have been muchsmaller in amplitude. Gravity monitoring is able todiscriminate between steam zone dry-out and steamzone resaturation. However the amplitude of gravityincreases associated with individual injection wells isoften small and may not be resolvable with annualsurveys. Once fields have passed their initialpressure-drawdown phase and the rate of gravitychange decreases, the frequency of gravity surveysshould be decreased.

Authors 
R. G. Allis, P. Gettings and D. S. Chapman






Conference 
Proceedings Twenty-Fitfh Workshop on Geothermal Reservoir Enggineering, Stanford University, Stanford California; Stanford University; 2000


Published 
Proceedings Twenty-Fitfh Workshop on Geothermal Reservoir Enggineering, Stanford University, Stanford California;, 2000





DOI 
Not Provided
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Online 
Internet link for Precise Gravimetry and Geothermal Reservoir Management

Citation

R. G. Allis,P. Gettings,D. S. Chapman. 2000. Precise Gravimetry and Geothermal Reservoir Management. In: Proceedings Twenty-Fitfh Workshop on Geothermal Reservoir Enggineering, Stanford University, Stanford California. Proceedings Twenty-Fitfh Workshop on Geothermal Reservoir Enggineering, Stanford University, Stanford California; 2000; Stanford University. Stanford University: (!) ; p. (!)


Related Geothermal Exploration Activities
Activities (1)


Areas (1)
  1. Dixie Valley Geothermal Area
Regions (0)