Reservoir evalutation of the Ölkelduháls geothermal field, Hengill area, SW-Iceland

Abstract

In order to produce viably from a given geothermal reservoir, one needs to know its deliverability, properties and size. The Ölkelduháls geothermal field is one of at least seven geothermal fields in the Hengill high-temperature area in SW-Iceland located about 35 km east of Reykjavík, just north of the town of Hveragerdi. This field belongs to Orkuveita Reykjavíkur (Reykjavik Energy). Warm-up and injection transient test and temperature and pressure profiles from well HE-20, exploration well ÖJ-1 and the recently drilled well HE-22 were used for estimating reservoir parameters, determining deliverability and establishing some of the reservoir’s natural state concepts for a model. In HE-20, the pressure control point was manifested at about 1500 m depth, near the main feedzones which are located at about 1400 and 1600 m depth. Estimates of formation temperatures and initial reservoir pressures at these depths were obtained using the Horner method and the program PREDYP and found to be about 250°C and 85 bar-g, respectively. Using non-linear regression, the derivative plot, Theis solution, multiple rate techniques and type curve matching, fall-off and injection step test data were used to infer the permeability-thickness (kh) in the range from 9 to 84 Dm, storativity about 3 × 10-8 m/Pa.s, whereas skin was deduced between 0 and -3. The limits of the reservoir could not be determined and analyses could not establish whether the boundaries were open or closed. However, the radius of investigation for the period of the tests was evaluated as 3.6 km. Previous resistivity surveys approximate the reservoir at 20 km2 in area. The deliverability of well HE-20 was determined by the Russell James critical lip pressure method and through simulation using the HOLA wellbore simulator. For the period of discharge, with a reservoir pressure of .........