Gas Geothermometry for Drilhole Fluids from Vapor Dominated and Hot Water Geothermal Fields
The compositions of steam from the vapor-dominated geothermal systems of Larderello, Italy and The Geysers, California have been shown by previous investigators to vary with position in the field. The most conspicuous chemical patterns observed in the Larderello and The Geysers vapor-dominated geotherrnal are strong increases or decreases from the center to the edges of constituents carried in the steam. The pattern of these parameters in vapor-dominated systems seem to be controlled mainly by a process of lateral steam movement and condensation. The condensation process, at constant temperature and total pressure increases the partial pressure of CO{sub 2} at the same rate as the gas/steam ratio, strongly affecting the composition of the total gas (including steam). The condensation effect should increase contents of CO{sub 2}, H{sub 2}S, H{sub 2} and CH{sub 4} in the residual steam to about the same degree because their solubilities are similar. However, the general trend observed is almost constant ratios of H{sub 2}S, H{sub 2}, CH{sub 4} to H{sub 2}O as the CO{sub 2}/H{sub 2}O ratio increases in Larderello about 5-6 times from the center to the edges at constant temperature. This means that the H{sub 2}/CO{sub 2}, CH{sub 4}/CO{sub 2}, and H{sub 2}S/CO{sub 2} ratios decrease with increasing CO{sub 2}/H{sub 2}O ratios. Apparently the only rnechanism that can explain this behavior is reaction of these three gases with other gases and with reservoir minerals so that the partial pressures of these gases are buffered by temperature-dependent reactions with water and rock minerals. A system of appropriate equations involving H{sub 2}O, CO{sub 2}, H{sub 2}. CH{sub 4}, H{sub 2}S were set up. The geothermometers have been tested on data from the Italian fields of Larderello, Travale, Bagnore, Piancastagnaio and from The Geysers, U.S.A. The gas geothermometers have been applied t o steam samples from wells FBN and ALR in order to define changes in both well and reservoir temperatures. The H{sub 2}S geothermometer appears to give results consistant with liquid-based geothermometers.
- Research Organization:
- IIRG-CNR, Pisa, Italy; U.S. Geological Survery, Menlo Park, CA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AT03-80SF11459
- OSTI ID:
- 889283
- Report Number(s):
- SGP-TR-50-48
- Country of Publication:
- United States
- Language:
- English
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