Early Calcite Dissolution as a Major Control on Porosity Development in The Geysers Steam Field, California -- Additional Evidence in Core from Unocal Well NEGU-17
- Key words
- Exploration; USA; California; Hydrothermal; Liquid Dominated; Carbonate; High Temperature; Reservoir Models; Reserves; Porosity; Quartz; Vein; Mineralization; CO2; Calcite; Franciscan; Metagraywacke
- Location
- The Geysers, California
- Conference
- Geothermal Resources Council Transactions
- Year
- 1992
- Session
- Exploration; Calcite; Porosity; Core sampling; Lithology; Hy
- Language
- English
Abstract
Detailed characterization of core from Unocal Corporation well NEGU-17 in the Geysers steam field has strengthened our belief that hydrothermal dissolution of Franciscan (lat Mesozoic) vein calcite and possibly aragonite created substantial matrix porosity on a field wide basis. This paragenetically early carbonate dissolution took place in a liquid dominated, high temperature hydrothermal system immediately antedating the modern steam reservoir. Not only was the Franciscan carbonate extensively dissolved, but resulting voids were lined or filled by porous cal-silicate aggregates with very high surface areas conductive to water absorption. In progress quantification of the abundances, geometries, and surface area of these other crystal lined voids in the Geysers cores should help provide realistic constraints for those modeling the field's performance and ultimate reserves.
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