Cement De-bonding Under Elevated Temperature Conditions: What Is Different?

Abstract

Geothermal wells rely on hydraulic fracturing in order to enhance the heat exchange downhole. However, when hydraulic fracturing is performed the injection fluid is typical lowering the temperature in the near wellbore area, resulting in possible loss of wellbore integrity. A very controversial aspect is the effect of heating and cooling on cement properties, particularly related to interfacial bonding strength. A novel experimental setup has been developed to compare cement interfacial de-bonding with cement shear during the geothermal well exploitation. This setup allows the evaluation of bonding and shear stresses between cement and casing, and could help the improvement of casing movement models. The samples are cured at elevated temperature (around 80 deg C) and then cooled down by immersing them in room temperature water bad. After the sample temperature stabilizes, the samples are then tested. This paper will present the latest results of interfacial cement shear stress and the pure cement shear stress that were performed at elevated temperatures mimicking the natural cycle of a geothermal well: drilling, cementing, wait on cement, fracturing, production. The results will be compared with reference samples kept at room temperature.