Flow Test At Long Valley Caldera Geothermal Area (Farrar, Et Al., 2003)
Exploration Activity: Flow Test At Long Valley Caldera Geothermal Area (Farrar, Et Al., 2003)
|Exploration Activity Details|
|Location||Long Valley Caldera Geothermal Area|
|Exploration Technique||Flow Test|
|Activity Date||2000 - 2001|
The study integrates detailed results from pump tests, fluid level monitoring, temperature logging, and fluid sampling/analysis of the LVEW with information obtained from other wells drilled on or near the resurgent dome to provide a comprehensive conceptual model of the different stages of hydrothermal activity, flow, and recharge in the Long Valley caldera groundwater system.
Pumping tests of the LVEW were conducted in May and July 2000 to evaluate the pumping and fluid disposal systems. These tests used a submersible downhole pump, pressure transducer, and thermistor tool set at approximately 400 m depth. Pressure measurements obtained during these tests revealed that adequate data analysis would require installation of a pressure transducer near the fracture zone to reduce the effects of temperature and variations in fluid density on the measurements. Installation of a pressure transducer designed and built by Sandia National Laboratory at 2600 m depth was completed on September 7, 2001. Pumping was resumed on September 9th following replacement of an electric generator that failed the previous day. The well was pumped at an average rate of 0.70 L/s for 50 hours, and was then monitored through a recovery period that lasted an additional 24 hours. This final flow test provided the most complete dataset of all the tests run, and so data from the September 9-12 test are used in subsequent pressure modeling calculations. Flow rates measured during the test were between 0.66 and 0.74 L/s. Frequent variations in the measured flow rate relate to the effects of gas entrained in the discharge line on the flow meter, and so pressure data were reduced by fitting a 30-point moving average curve to the data for the purpose of estimating flow rate variations in the flow model. Total measured drawdown over the course of the test was 0.32 MPa, with a brief period of flattening and slight pressure rise at 24 hours related in part to declining flow rates. Flow rates and drawdown increased following a brief 1.5 hour interruption in flow measures caused by a burst pipe at 32 hours, then drawdown stabilized at approximately 42 hours.
- Christopher D. Farrar, Michael L. Sorey, Evelyn Roeloffs, Devin L. Galloway, James F. Howle, Ronald Jacobson (2003) Inferences On The Hydrothermal System Beneath The Resurgent Dome In Long Valley Caldera, East-Central California, USA, From Recent Pumping Tests And Geochemical Sampling