| Abstract |
Formation permeabilities are usually determined from pressure transient tests or laboratory measurements on drill cores. The use of geothermal inflow type-curves may be a viable alternative to estimate this reservoir parameter. The inflow type-curves relate produced mass flowrate to flowing pressure in the feed zone of the well. By superposition of the inflow curve of a geothermal well with geothermal inflow type curves it is possible to estimate the absolute formation permeability at the feed-zone of the well. The permeability value implicit in the type-curve of the best match is then the permeability value sought. This methodology does not require field measurement of the inflow curve of the well. Use of two geothermal inflow performance dimensionless reference curves, one for mass productivity and another for thermal productivity, allows calculation of the well complete inflow curve, when combined with reservoir static pressure P0 and a single measurement of mass flowrate, flowing pressure and specific enthalpy (W,P,h)0 at the well feed-zone or at the wellhead. In order to do this, a computation system was developed which is described in this work. The system makes it possible to overlap the geothermal well inflow curve on to different geothermal inflow type-curves and then to select the best possible match. Type-curves covering the temperature range from 200 to 350?C in 25?C increments and Corey and linear relative permeabilities were considered. The system also allows estimation of the output curves associated to 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 proposed 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. This system can be considered as a complementary tool to the laboratory measurement of permeability and to the transient pressure tests as well as to well analysis. |