Location of Production Zones with Pressure Gradient Logging

Abstract

The fact that geothermal wells produce from only a l imited number of discrete fractures o r "feed zones" often gives rise to confusing temperature and pressure logs. This is because the wells frequently are flowing from one zone to another while the measurements are made--even though the well is shut in. Interpretation of the temperature and pressure logs is then difficult unless the location of the feed zones can be determined and the internal flows recognized. Although this may often be determined by an experienced reservoir engineer there remains considerable room for ambiguity. This paper presents a method for locating the feed zones and simultaneously registering upward or downward flows by comparing the measured pressure gradient with the hydrostatic gradient calculated from a simultaneously run temperature log. Demonstration of the technique in Cerro Prieto is shown.