Analysis of the effect of steam injection conditions on the integrity of casing-cement sheath-formation assemblies in heavy oil thermal recovery

Accurately forecasting the sealing failure behavior of the casing-cement sheath-formation assembly under various steam injection operational parameters and cyclic steam stimulation conditions remains challenging. Such unpredictability heightens the risk of seal integrity compromise in the wellbores of thermal heavy oil production. This paper develops a numerical simulation and analytical approach based on heat-fluid-solid interactions within the casing-cement sheath-formation system. It assesses the impact of potential cement sheath and interfacial failures in response to differing steam injection pressures, temperatures, injection rates, and cyclic steam volumes. This assessment leverages the established relationships between the temperature-dependent elastic modulus and Poisson's ratio of cementitious materials, as well as the dynamics of wellbore pressure, temperature, and steam quality during steam injection. Experimental findings suggest that maintaining steam injection temperatures between 340-380°Ccan effectively mitigate the risk of shear-induced damage and enhance the safety of the cementing interface. The injection rate appears to have a minimal impact on interface integrity. The extent of plastic strain in the cement sheath is proportionate to the size of the micro-annular gap at the interface. When the initial formation has an elastic modulus of 15 GPa, variations in the cement sheath's elastic modulus do not influence the micro-annular gap size. However, in formations with an initial elastic modulus of 5 GPa, a lower elastic modulus of the cement sheath corresponds to a smaller micro-annular gap. The study concludes that a higher initial geostress and temperature, coupled with a high elastic modulus of the surrounding strata, are conducive to maintaining the integrity of the cement sheath interface.