Use of Pressure-Temperature-Spinner Surveys to Characterize Geothermal Production Well Behavior

Abstract

In the Mak-Ban and Tiwi geothermal fields operated by Philippine Geothermal Production Company, Inc. (PGPC), there is now a significant database of Pressure-Temperature-Spinner (PTS) surveys conducted in both steam and two-phase production wells as well as injection wells. Normally a series of surveys are run on a well, including uplogs and downlogs at two or more logging speeds to characterize the flow conditions and provide the necessary information to convert the measured spinner velocities to mass flow. Stationary runs may also be conducted at various locations to check if flow is occurring at that location and if it is upflowing or downflowing. In the majority of wells, the results from the PTS surveys normally indicate that downhole flow conditions are stable and the surveys are relatively easy to analyze to provide information on permeable zone locations and thermodynamic conditions. However, in both Mak-Ban and Tiwi, there are a number of wells that exhibit unstable well behavior and this is normally manifested by cycling or spikes in the wellhead pressure and associated changes in production flow rates and enthalpies although in some wells, changes in wellhead conditions may not be apparent. PTS surveys have been run to help characterize the downhole conditions in these wells and the results obtained have in many cases been quite surprising in terms of how dynamic the conditions can be in the wellbore. In some wells, very unstable spinner responses have been measured in regions of the well that suggest counterflow is occurring. In other wells, there are significant changes in the PTS profiles from one survey to the next as the fluid changes from being predominantly two-phase to almost single-phase liquid while the survey is being conducted. In many of these cases, quantitative analysis may not be possible but the surveys still provide qualitative information that helps in understanding the well’s characteristics.