Analysis of Production Data from the Krafla Geothermal Field, Iceland

Abstract

The Krafla geothermal field in northeastern Iceland consists of several zones, which contain fluids of different composition and thermodynamic state (Stefansson, 1981). In this paper we examine production data from wells which are completed in two-phase zones. Transient changes in flow rate and flowing enthalpy are analyzed to obtain insight into relative ( liquid and gas phase) permeabilities, and other reservoir parameters. Numerous studies have shown that predictions of geothermal reservoir behavior are strongly dependent upon the choice of r e l at i v e permeability functions. There is an extensive literature on gas-oil and o i l - water relative permeabilities, but steam-water r e l at i v e perm e a b i l i t i e s which are needed for geothermal r e servoir analysis are poorly known. (1978) and Counsil and Ramey (1979) have provided some data which, however, seem to be at variance with relative permeability characteristics deduced from field data by Grant (1977) and Horne and Ramey (1978). The differences may reflect uncertainties in the analysis methods used, or they may reflect " real " differences i nrel at i v e permeability behavior of fractured reservoirs from that of porous medium-type laboratory cores. Recent theoretical work by Menzies (1982) and Gudmundsson et a l. (1983) has substantiated the relative permeability characteristic s obtained by Horne and Ramey (1978) for Wairakei wells. Laboratory experiments by Chen et a l .