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Description
The interpretation of well tests or long-term observations of wellhead parameters is an extremely valuable tool in the correct assessment of the hydraulic capacity of geothermal reservoir. Despite using the same relationships describing mechanisms of water flow as in the case of freshwater or oil, an important factor that introduces a certain correction to the interpretation of pumping data in geothermal wells is the influence of temperature on the water density. Large fluctuations in water or brine temperature while pumping the well significantly disturb the readings of recorded data - the dynamic water level or the wellhead pressure. This phenomenon is called thermal lift effect.
It often happens that in the case of deep wells with good filtration parameters of the aquifer, the shape of the drawdown curve is far from expectations, because the effect of water expansions masks the true drawdown. The deeper the well and the higher the bottomhole temperature, the more significant this effect is. In any case, the thermal lift effect always causes the drawdown to be smaller than it would be observed if there was no volumetric expansion of water. This in turn can lead to overestimation of resources and unsustainable exploitation, because the real drawdown is often miscalculated. Therefore, it is good practice to separate the thermal lift effect from the raw data when interpreting both short- and long-term pumping data. This allows to filter out noise, correctly assess the actual drawdown, and as a result - the correct transmissivity of the aquifer.
As part of the GeoModel project, THERMALIFT calculator was developed. This Python tool allows for the correction of raw pumping data and graphical representation of results on charts. The only input data required are temperature and water or pressure level during pumping and the temperature profile along the well under natural conditions. The tool was designed to work with vertical and deviated wells with freshwaters and brines. However, the tool is not designed for 2-phase wells. The Python code is in the advanced phase of development and the documentation and user’s manual should be soon available on project website www.geomodel.pl/en
