ABSTRACT: Water Injection Operations and Studies in the Geysers Geothermal Field

B. J. Barker, J. J. Maney, D. J. Camille, K. H. Williamson

Water injection into the steam reservoir at The Geysers began in 1969 for powerplant condensate disposal. The 82 MW installed capacity at that time has since grown to 2043 MW, of which 1103 MW is supplied by the Unocal-NEC-Thermal (U-N-T)joint venture. All of these plants rely on injection into the reservoir for excess condensate disposal, with the condensate stream also used to carry dissolved noxious gasses such as ammonia and hydrogen sulfide.

Production interference and corrosion are frequent operating problems. However, the potential for secondary heat recovery prompted U-N-T in 1980 to begin pumping extra water from Big Sulphur Creek during the winter months of high runoff. Total injection averages 27% of mass produced. Plant condensate alone averages 24%.

Numerous tracer studies have been conducted in the field, most notably using tritium. These studies confirm high lateral permeability over broad areas and suggest a mobile liquid phase at depth. Isotope trends have been used to constrain a numerical reservoir model, which gives estimates of long-term production contributions.

Production response indicates that injected water is recovered as steam over a period of several years. Because the recovery period is long and injection facilities costly, current low energy prices do not justify developing major new water sources. In the absence of any new, inexpensive water source, additional steam supplies from supplemental water injection will be small.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990