A co-optimization method of equivalent circulating density and displacement efficiency in managed pressure cementing phase considering casing eccentricity

Equivalent circulating density (ECD) and displacement efficiency are critical for cementing quality. First, the ECD prediction model for the injection stage of managed pressure cementing was established by considering the density and rheology of different types of fluids. Subsequently, an eccentric annulus injection cement displacement efficiency model was developed with the objective of predicting the mixing length. Finally, the key equations for co-optimization were given by considering these physical quantities. The model was validated using well A data, and in the early, middle, and late stages of cement injection, the average relative errors of pressure prediction were 3.55%, 2.47%, and 5.36%, respectively. The temperature field, ECD, mixing length, and optimization parameters were predicted and analyzed. The results show that the fluid temperature in the annulus is higher than that in the casing, the magnitude of wellbore temperature change is getting smaller and smaller, and the temperature field of the wellbore and formation is moving toward thermal equilibrium. The bottomhole ECD after pressure control is always within the safe density window. During the top injection process, the mixing length can reach 200 m, and the cement slurry has a shorter mixing length under turbulent flow. Accordingly, the key parameters were optimized, and the optimized injection scheme has higher displacement efficiency and meets the requirement of bottomhole pressure balance. The results of the study will provide theoretical basis for the optimization of cementing injection parameters.