Estimating Individual Injectivity Indices for Two or More Feed-Zones in Geothermal Wells

Abstract

Spinner logs are widely used for feed zone analysis in geothermal wells, both for location and permeability purposes. Traditionally, temperature logs have been used as a major basis for feed zone location and co-interpreted with circulation loss information during the drilling process, qualitative feed zone size has been estimated. In 2012 spinner logs were added to ÍSOR´s logging toolbox for supporting and improving feed zone analysis of geothermal wells. The feed zone analysis scheme introduced is based on a well-known fluid velocity determination with spinner logs and it assumes the same well diameter above and below each feed zone recognized from a change in fluid velocity. Up and down spinner-logs combined with corresponding pressure log at two different flow rates form the basis for a quantitative feed zone analysis to determine the injectivity index of individual feed zones. With a good quality spinner log, added feed zone indices accurately fit the total injectivity index obtained in a conventional injectivity test