Understanding the heat transfer phenomena encountered in extreme oil and gas reservoir environments [i.e., thermal recovery, high-pressure/high-temperature (HP/HT), deepwater, etc.] and geothermal wells is important to enhance the exploration and production of subterranean energy resources. However, there can be a lack of information about thermal properties of current oilwell cement systems, which are key inputs for any cement sheath stress simulator that accounts for the thermal cycling effect on the integrity of the annular sealant. Having thermal data for multiple sealant systems is important to allow for risk reduction and production maximization by reducing wellbore construction uncertainty during the planning stage, therefore allowing operators to make well-informed decisions.
This paper discusses the thermal conductivity and thermal expansion of neat, foamed, and elastic oilwell cements. These properties were measured in hydrated and dehydrated states at ambient pressure and at temperatures ranging from 25 to 100°C (77 to 212°F). Both thermal conductivity and thermal expansion measured on dehydrated cement samples were less than hydrated samples, which is most likely attributed to the effect of evaporable water within the cement specimens. Mathematical relationships were derived for thermal and physical (i.e., density) properties of cement, thus allowing for approximate characterization of the thermal behavior of oilwell cements. The effect of the thermal properties of different cement systems on the integrity of a typical thermal recovery well was evaluated as a case study. Elastic properties of the aforementioned cement systems were also studied, yielding characteristic curves for each system. Moreover, the impact of cyclic loads on determining acceptable stress levels of annular sealants is also presented, along with its economic benefits. This allows for the optimal design of dependable sealants for long-term integrity during the planning stage.
