The Platinum Resistance Thermometer is used to give a high precision reading of wellbore temperature. It outputs temperature data as a digital word allowing for very high resolution. Because of the small size of the tip it also has a very rapid response time, which minimizes the effects of differing line speeds. It can be run alone, or as part of a string of Production Logging tools.
The change of resistance of a length of platinum wire with changing well temperature is used to drive a Voltage Controller Oscillator. The frequency output from the VCO is digitized and encoded on the line. The high thermal conductivity copper tip is isolated with a low thermal conductivity body, which allows for high-resolution measurement even with high differential temperatures between the well fluid and the tool body.
When downhole pressure is lower than bubble point pressure, associated gas is released. This gas could result in a temperature anomaly due to Joule – Thomson effect as shown in the plot opposite.
This plot indicates flow behind casing at 240m3/d flow rates.
The temperature curve shows flow behind the casing from 3800m down to 4176-4180m, where it enter the casing.