Gases and water isotopes in a geochemical section across the Larderello,Italy, geothermal field |
| |
| Authors: | Alfred H Truesdell Nancy L Nehring |
| |
| Institution: | 1. U.S. Geological Survey, 345 Middlefield Road, 94025, Menlo Park, California, USA
|
| |
| Abstract: | Steam samples from six wells (Colombaia, Pineta, Larderello 57, Larderello 155, Gabbro 6, and Gabbro 1) in a south to north section across the Larderello geothermal field have been analyzed for inorganic and hydrocarbon gases and for oxygen-18 and deuterium of steam. The wells generally decrease in depth and increase in age toward the south. The steam samples are generally characterized by - Total gas contents increasing south to north from 0.003 to 0.05 mole fraction;
- Constant CO2 (95±2 percent); near constant H2S (1.6±0.8), N2 (1.2±0.8), H2 (2±1), CH4 (1.2±1), and no O2 in the dry gas;
- Presence of numerous, straight chain and branched C2 to C6 hydrocarbons plus benzene in amounts independent of CH4 contents with highest concentrations in the deeper wells;
- Oxygen-18 contents of steam increasing south to north from ?5.0‰ to ?0.4‰ with little change in deuterium (?42±2‰).
These observations are interpreted as showing: - Decreasing gas contents with amount of production because the proportion of steam boiled from liquid water increases with production;
- Synthesis of CH4 from H2 and CO2 with CO2 and H2 produced by thermal metamorphism and rock-water reactions;
- Extraction of C2 to C6 hydrocarbons from rock organic matter;
- Either oxygen isotope exchange followed by distillation of steam from the north toward the south (2 plates at ～220°C) or mixture of deeper more-exchange waters from the north with shallow, less-exchanged recharging waters from the south.
|
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
