Computational system to estimate formation permeabilities and output curves of geothermal wells

Geothermal Inflow Performance Relationships (GIPR) numerically obtained may be used to estimate formation permeability at the geothermal well feed zone, by superimposition of the well inflow curve with different GIPR curves (geothermal inflow type-curves). Each type-curve reflects behavior which depends on the formation properties. The methodology 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), flowing pressure (P) and specific enthalpy (h), (W,P,h)(0), and from the static pressure at the well feed zone (P-s), by using two geothermal inflow performance dimensionless reference curves, one for mass productivity and another for thermal productivity. In order to facilitate the permeability diagnostic by means of this methodology, a computation system was developed which is described in this work. The system makes it possible to superimpose the geothermal well inflow curve on different geothermal inflow type-curves and then to select the best possible fit. Type-curves integrated to the system covering the temperature range 200-350degreesC in 25degreesC increments and Corey and linear relative permeabilities were considered. The system also allows estimation of the output curves associated with the well inflow curve by considering each calculated point of the well inflow curve as the input of a geothermal well flow simulator. The computation system shows instantaneously the estimated mass output curve (mass deliverability curve) for the well under analysis and the corresponding thermal power and specific enthalpy output curves. When it is required to validate the methodology for a particular well, the (W, P, h)(0) data may be from a previous discharge test and then the system will display the estimated output curves comparing them with all the field data of the corresponding discharge test. It is expected that this system can be considered as a complementary tool to the laboratory measurements of permeability and to the transient pressure tests as well as to well analysis. (C) 2003 Elsevier Ltd. All rights reserved.