Accurate Location of Feed Zones: Assessing Obscuration by the Liner in Geothermal Wells

Abstract

Feed zones in geothermal wells are typically identified primarily from pressure, temperature and spinner (PTS) data captured with a downhole tool during completion testing, when water is being injected into the well. Completion testing usually occurs after the slotted liner has been installed in the well, and it is frequently assumed that feed zone locations are at least partially obscured by the presence of the liner. In some wells there is also stage testing during drilling, to aid the decision on whether to continue drilling or not. Critically, stage testing occurs prior to the installation of the liner, and also captures PTS data. Some stage testing only captures data within the well casing down to the casing shoe. However, there are a number of examples with sufficient PTS data captured in the open-hole section to allow comparison to the results from completion testing. These examples show that the location and nature of the feed zones can be seen in much finer detail when the liner is not present.
The aim of this research is to quantify the degree to which the liner obscures the feed zone locations by comparing temperature logs acquired during open-hole testing (stage testing) with those acquired after liner installation (completion testing). Several field examples are presented, from liquid-dominated wells in the Taup? Volcanic Zone.