The Sondex Capacitance Water Hold‑up Tool essentially measures the proportion of water in the well fluid. The design of the fluid flow path through the tool ensures representative sampling of the fluid in the well and ease of cleaning. The tool is most responsive up to 45% water cut, above which it starts to saturate as the conductive phase becomes dominant. In high water cut flows presentation scales can be expanded to indicate hydrocarbon entry that may not be detected by density tools. Also, though the tool is primarily a water holdup tool, because the tool has slightly different frequencies in gas and oil, in water free high Gas Oil Ratio wells it can be used to emulate a density tool as an indicator of GOR, but with higher resolution.
The tool is essentially an annular capacitor with the central probe and external cage acting as the capacitor plates and the well fluid flowing between the plates as the dielectric. Water has a high dielectric constant and hydrocarbons have low dielectric constants thus the output frequency of the tool changes in relation to the changing average dielectric constant, or water / hydrocarbon ratio, of the fluid flowing through the tool. Water holdup is determined by reference to a holdup / fractional response chart.
The plot opposite shows the productive zones against the fractured zones observed clearly by CAST-V in the White Tiger fractured basement reservoir
Entry of fluid is clearly indicated in the permeable zone as per CFBRATE, DENR and CWHRATE.