Elimination of the Thermal Lift Effect from Pumping Observations in Deep Geothermal Wells

Abstract

During the pumping of geothermal wells, water at the wellhead may reach a temperature close to the bottomhole conditions, especially when the flow rate is high and the pumping time is long enough. As a result of the pumping, the mean temperature of the fluid in the well rises, causing the average density of fluid to decrease. The volumetric expansion of water due to temperature rise - called the thermal lift effect - often disturbs the readings of the wellhead pressure or the water level. 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. 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. 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 CAC was developed. This Python tool allows for the correction of raw pumping data and graphical representation of results on charts. The tool was designed to work with liquid-only wells for both freshwaters and brines.