Influence of Cement Thermal Properties on Wellbore Heat Exchange

Abstract

Cementing geothermal wells is not an easy task. Besides the high temperature environment that affects the curing time of the cement, the cement sheath behind the casing, which is used primarily to protect and hydraulically seal the wellbore, influences the heat exchange from the wellbore to the formation and vice-versa. Depending on the geothermal operation, high or low heat exchanges might be preferred. For example, operators aim for a high and constant heat exchange in the lower part of a geothermal well and will try to insulate the upper part of the same well in order to minimize heat and efficiency losses accordingly. This study focuses on the ability of different cements’ thermal conductivities to influence the heat exchange in various wellbore segments under assumed static conditions. Sensitivities indicate which parameters play crucial roles while modeling the heat transfer in high temperature boreholes. Via Monte Carlo simulation, the relative importance of diverse thermal and geometrical parameters is considered when calculating the rock formation/wellbore heat exchange. The modeling highlighted the presence of a ‘working window' in which the variation of the thermal or geometrical parameters can strongly influence the borehole-formation heat exchange. Finally, the paper provides the optimum cement thermal properties required to properly cement a geothermal well and so minimize/enhance heat exchange to/from the wellbore.