Theoretical and Experimental Study on Cementing Displacement Interface for Highly Deviated Wells

An effective drilling fluid removal is necessary to achieve an efficient cementing in oil and gas industry, i.e., it is ideal that all the drilling fluid is displaced by the cement slurry. The displacement efficiency is closely related to the stability and development of the displacing interface between the cementing slurry and drilling fluid. Thus, an effective cementing requires a validated theoretical model to describe the displacing interface to guide cementing applications, especially for highly deviated wells. The current studies suffer from a lack of experimental validation for proposed models. In this study, a theoretical model of cementing interfacial displacement in eccentric annulus is established. An experimental study is conducted to examine effects of well inclination, eccentricity and fluid properties on the stability of displacement interface to verify the theoretical model. The model is found to well describe the interface in the eccentric annulus, and it is applicable to the wellbore annulus with different inclination angles. The results show that: the displacement interface gradually extends (i.e., length is increased) with the increase of well inclination; the cement displacement effect became worse with deviation angle under the same injection and replacement conditions. Increasing the apparent viscosity of cement slurry is beneficial to improve the stability of displacement interface. In highly deviated wells, a certain casing eccentricity can inhibit the penetration of cement slurry in the wide gap of the low side of the annulus, which is conducive to maintaining the stability of the displacement interface.