Formation permeability at the feedzone of geothermal wells employing inflow type-curves

Abstract

Geothermal Inflow Performance Relationships (GIPR) may be used to estimate formation permeability, by overlapping the well inflow curve with different theoretical GIPR curves. This method does not require field measurement of the well inflow curve. The complete well inflow curve is obtained from a single wellhead or bottomhole measurement of mass flowrate (W), pressure (P) and specific enthalpy (h), and from the static pressure at the well feedzone (Ps). Wellhead data of previous discharge tests from six wells of the Los Azufres geothermal field are used. The permeabilities obtained by the proposed method are in the right range as referred to a reservoir thickness of 100 m. The difference between calculated and field data is on the order of 6% for wellhead pressure and 2% for specific enthalpy when uncertainty of the field data is low. Inflow type-curves include the effects of undisturbed reservoir initial conditions, fluid and formation properties and cumulative mass production, for two-phase inflow. Skin effects were disregarded.