Field Study of Tracer and Geochemistry Behavior During Hydraulic Fracturing of a Hot Dry Rock Geothermal Reservoir

摘要

This study presents tracer and geochemistry data from several hydraulic fracturing experiments at the Fenton Hill, NM, HDR geothermal reservoir. Tracers have been injected at various times during these tests: (1) initially, before any flow communication existed between the wells; (2) shortly after a flow connection was established; and (3) after the outlet flow had increased to its steady state value. An idealized flow model consisting of a combination of main fracture flow paths and fluid leakoff into secondary permeability explains the different tracer response curves for these cases, and allows us to predict the fracture volume of the main paths. The geochemistry during these experiments supports our previously developed models postulating the existence of a high concentration indigenous ''pore fluid.'' Also, the quartz and Na-K-Ca geothermometers have been used successfully to identify the temperatures and depths at which fluid traveled while in the reservoir. The quartz geothermometer is somewhat more reliable because at these high temperatures (about 250 deg C) the injected fluid can come to equilibrium with quartz in the reservoir. The Na-K-Ca geothermometer relies on obtaining a sample of the indigenous pore fluid, and thus is somewhat susceptible to problems of dilution with the injection fluid. 14 refs., 6 figs., 1 tab. (ERA citation 11:019597)