Summary of recent flow testing of the Fenton Hill HDR reservoir

Abstract

A sequence of reservoir flow tests has been conducted at the Fenton Hill Hot Dry Rock (HDR) test site as part of the Long-Term Flow Testing (LTFT) program. This testing, which extended over an aggregate period of about 8 months, has demonstrated several significant features concerning HDR reservoirs that taken together reflect very positively on the future development of the HDR concept into a viable commercial reality. Of most significance is the demonstrated self-regulating nature of the flow through such a reservoir. Both temperature and tracer data indicate that the flow, rather than concentrating in a few potential direct flow paths, progressively shifted towards more indirect flow paths as the test proceeded. This self-regulating mechanism may be related to the strongly temperature-dependent viscosity of water. Measurements have shown that the reservoir flow impedance is concentrated in the near-wellbore region surrounding the production well. This situation may well be a blessing in disguise since this suggests that the distance between injection and production wells can be significantly increased, with a greatly enhanced access to fractured hot rock, without an undue impedance penalty. However, since the multiply interconnected joints within the HDR reservoir are held open by fluid pressure, a higher meanmore » reservoir pressure is the obvious path to increased productivity while still retaining the distributed nature of the flow. Other significant observations include a very small rate of reservoir water loss that was still declining at the end of the flow testing, and a set of temperature measurements in the production well that show no significant temperature drawdown during the period of testing.« less