The energy demand is increasing around the globe, and while oil and gas continue to play a main part in the energy impact, renewables are taking place as important contributors. In addition to this, the net-zero policy by 2050 developed in the United States is leaning the efforts towards cleaner energies. In that respect, geothermal will play an important function due to the untapped resources and presence around the world. Geothermal, as well as oil and gas operations, comes with different operational challenges, such as depth, which makes subsurface conditions very aggressive with respect to temperature and pressure. Therefore, to successfully perform geothermal operations, the integrity of the well needs to be assured.

Casing and cement play a crucial role in terms of well integrity, as many studies have suggested. Moreover, the elevated temperatures in geothermal operations make thermal properties on these components a parameter of utmost importance, something not widely investigated in comparison with mechanical properties. Thermal expansion is a thermal property with an important impact in the integrity of the wells, which might be jeopardized due to the constant thermal loads effected in such operations. Effects in casing go up to the collapse of the tubular, while cement can suffer from micro-annuli, cracks or debonding.

This investigation focuses on the measurements of the coefficient of linear thermal expansion for oilwell cements, as well as other reference materials and rocks, with novel equipment developed in the Well Integrity Laboratory at The University of Oklahoma. This equipment, which uses an optical shadowing technique, provides faster coefficient of linear thermal expansion calculations in contrast to other equipment or techniques.

More than 300 measurements were performed in this investigation, which includes diverse materials and rocks, are performed not just to corroborate the reliability on the equipment, but also to create a comparison between the coefficient of linear thermal expansions found in diverse literature. The experiments are performed at high temperatures up to 200 ºC (400 ºF), which simulate the extreme temperature conditions encountered in deeper downhole conditions for oil and gas, as well as in geothermal processes. Additionally, characterization of this thermal property is performed for oilwell cement composites, creating a unique database for different mixtures in which different recipes, including neat Class C, G and H cement, as well as other recipes with added additives are comprised. Moreover, other aspects such as cyclic tests or curing times, which go from 14 days to 3 years, are varied.

In conclusion, the results generated by this novel equipment provide reliable coefficient of linear thermal expansion values, when associating them with the values found in different studies. Additionally, the comparison in the coefficient of linear thermal expansion values performed for the different cement composites shows the effects of curing time and cyclic loading for the coefficient in linear thermal expansion on oilwell cements. Several discussions are made based on the experiments conducted in this research.