| Title | Temporal Changes in Noble Gas Compositions Within the Aidlin Sector of The Geysers Geothermal System |
|---|---|
| Authors | Dobson, Patrick; Sonnenthal, Eric; Kennedy, Mack; van Soest, Thijs; Lewicki, Jennifer |
| Year | 2006 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Resource Characterization; Aidlin, noble gases, injection, reservoir modeling |
| Abstract | The use of nonreactive isotopic tracers coupled to a full thermal-hydrological reservoir simulation allows for an improved method of investigating how reservoir fluids contained within matrix and fractures contribute over time to fluids produced from geothermal systems. A combined field and modeling study has been initiated to evaluate the effects of injection, production, and fracture-matrix interaction on produced noble gas contents and isotopic ratios. Gas samples collected periodically from the Aidlin steam field at The Geysers, California, between 1997 and 2006 have been analyzed for their noble gas compositions, and reveal systematic shifts in abundance and isotopic ratios over time. Because of the low concentrations of helium dissolved in the injection waters, the injectate itself has little impact on the helium isotopic composition of the reservoir fluids over time. However, the injection process may lead to fracturing of reservoir rocks and an increase in diffusion-controlled variations in noble gas compositions, related to gases derived from fluids within the rock matrix. |